[v5,1/5] drm/ofdrm: Add ofdrm for Open Firmware framebuffers

Commit Message

Thomas Zimmermann Oct. 11, 2022, 3:07 p.m. UTC

Open Firmware provides basic display output via the 'display' node.
DT platform code already provides a device that represents the node's
framebuffer. Add a DRM driver for the device. The display mode and
color format is pre-initialized by the system's firmware. Runtime
modesetting via DRM is not possible. The display is useful during
early boot stages or as error fallback.

Similar functionality is already provided by fbdev's offb driver,
which is insufficient for modern userspace. The old driver includes
support for BootX device tree, which can be found on old 32-bit
PowerPC Macintosh systems. If these are still in use, the
functionality can be added to ofdrm or implemented in a new
driver. As with simpledrm, the fbdev driver cannot be selected if
ofdrm is already enabled.

Two notable points about the driver:

 * Reading the framebuffer aperture from the device tree is not
reliable on all systems. Ofdrm takes the heuristics and a comment
from offb to pick the correct range.

 * No resource management may be tied to the underlying PCI device.
Otherwise the handover to the native driver will fail with a resource
conflict. PCI management is therefore done as part of the platform
device's cleanup.

The driver has been tested on qemu's ppc64le emulation. The device
hand-over has been tested with bochs.

v5:
	* use drm_atomic_helper_check_crtc_primary_plane()
v4:
	* set preferred depth to the correct value
	* set bpp value for console emulation
	* output scanout-buffer parameters with drm_dbg()
v3:
	* reintegrate FWFB helpers into ofdrm
	* use damage iterator
	* sync GEM BOs with drm_gem_fb_{begin,end}_cpu_access()
	* fix various atomic_check helpers
	* remove CRTC atomic_{enable,disable} (Javier)
	* compute stride with drm_format_info_min_pitch() (Daniel)
v2:
	* removed simple-pipe helpers
	* built driver on top of FWFB helpers
	* merged all init code into single function
	* make PCI support optional (Michal)
	* support COMPILE_TEST (Javier)

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>

convert
---
 MAINTAINERS                   |   1 +
 drivers/gpu/drm/tiny/Kconfig  |  13 +
 drivers/gpu/drm/tiny/Makefile |   1 +
 drivers/gpu/drm/tiny/ofdrm.c  | 763 ++++++++++++++++++++++++++++++++++
 drivers/video/fbdev/Kconfig   |   1 +
 5 files changed, 779 insertions(+)
 create mode 100644 drivers/gpu/drm/tiny/ofdrm.c

Comments

Michal Suchánek Nov. 19, 2022, 3:25 p.m. UTC | #1

Hello,

On Tue, Oct 11, 2022 at 05:07:08PM +0200, Thomas Zimmermann wrote:
> Open Firmware provides basic display output via the 'display' node.
> DT platform code already provides a device that represents the node's
> framebuffer. Add a DRM driver for the device. The display mode and
> color format is pre-initialized by the system's firmware. Runtime
> modesetting via DRM is not possible. The display is useful during
> early boot stages or as error fallback.
> 
> Similar functionality is already provided by fbdev's offb driver,
> which is insufficient for modern userspace. The old driver includes
> support for BootX device tree, which can be found on old 32-bit
> PowerPC Macintosh systems. If these are still in use, the
> functionality can be added to ofdrm or implemented in a new
> driver. As with simpledrm, the fbdev driver cannot be selected if
> ofdrm is already enabled.
> 
> Two notable points about the driver:
> 
>  * Reading the framebuffer aperture from the device tree is not
> reliable on all systems. Ofdrm takes the heuristics and a comment
> from offb to pick the correct range.
> 
>  * No resource management may be tied to the underlying PCI device.
> Otherwise the handover to the native driver will fail with a resource
> conflict. PCI management is therefore done as part of the platform
> device's cleanup.
> 
> The driver has been tested on qemu's ppc64le emulation. The device
> hand-over has been tested with bochs.
> 
> v5:
> 	* use drm_atomic_helper_check_crtc_primary_plane()
> v4:
> 	* set preferred depth to the correct value
> 	* set bpp value for console emulation
> 	* output scanout-buffer parameters with drm_dbg()
> v3:
> 	* reintegrate FWFB helpers into ofdrm
> 	* use damage iterator
> 	* sync GEM BOs with drm_gem_fb_{begin,end}_cpu_access()
> 	* fix various atomic_check helpers
> 	* remove CRTC atomic_{enable,disable} (Javier)
> 	* compute stride with drm_format_info_min_pitch() (Daniel)
> v2:
> 	* removed simple-pipe helpers
> 	* built driver on top of FWFB helpers
> 	* merged all init code into single function
> 	* make PCI support optional (Michal)
> 	* support COMPILE_TEST (Javier)
> 
> Signed-off-by: Thomas Zimmermann <[e-mail]>
> Reviewed-by: Javier Martinez Canillas <[e-mail]>
> 
> convert
> ---
>  MAINTAINERS                   |   1 +
>  drivers/gpu/drm/tiny/Kconfig  |  13 +
>  drivers/gpu/drm/tiny/Makefile |   1 +
>  drivers/gpu/drm/tiny/ofdrm.c  | 763 ++++++++++++++++++++++++++++++++++
>  drivers/video/fbdev/Kconfig   |   1 +
>  5 files changed, 779 insertions(+)
>  create mode 100644 drivers/gpu/drm/tiny/ofdrm.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f07a8bf8744f..7c3bb04bd08e 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6656,6 +6656,7 @@ L:	[e-mail]
>  S:	Maintained
>  T:	git git://anongit.freedesktop.org/drm/drm-misc
>  F:	drivers/gpu/drm/drm_aperture.c
> +F:	drivers/gpu/drm/tiny/ofdrm.c
>  F:	drivers/gpu/drm/tiny/simpledrm.c
>  F:	drivers/video/aperture.c
>  F:	include/drm/drm_aperture.h
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 565957264875..a300b03a3c7a 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -51,6 +51,19 @@ config DRM_GM12U320
>  	 This is a KMS driver for projectors which use the GM12U320 chipset
>  	 for video transfer over USB2/3, such as the Acer C120 mini projector.
>  
> +config DRM_OFDRM
> +	tristate "Open Firmware display driver"
> +	depends on DRM && OF && (PPC || COMPILE_TEST)
> +	select APERTURE_HELPERS
> +	select DRM_GEM_SHMEM_HELPER
> +	select DRM_KMS_HELPER
> +	help
> +	  DRM driver for Open Firmware framebuffers.
> +
> +	  This driver assumes that the display hardware has been initialized
> +	  by the Open Firmware before the kernel boots. Scanout buffer, size,
> +	  and display format must be provided via device tree.
> +
>  config DRM_PANEL_MIPI_DBI
>  	tristate "DRM support for MIPI DBI compatible panels"
>  	depends on DRM && SPI
> diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
> index 1d9d6227e7ab..76dde89a044b 100644
> --- a/drivers/gpu/drm/tiny/Makefile
> +++ b/drivers/gpu/drm/tiny/Makefile
> @@ -4,6 +4,7 @@ obj-$(CONFIG_DRM_ARCPGU)		+= arcpgu.o
>  obj-$(CONFIG_DRM_BOCHS)			+= bochs.o
>  obj-$(CONFIG_DRM_CIRRUS_QEMU)		+= cirrus.o
>  obj-$(CONFIG_DRM_GM12U320)		+= gm12u320.o
> +obj-$(CONFIG_DRM_OFDRM)			+= ofdrm.o
>  obj-$(CONFIG_DRM_PANEL_MIPI_DBI)	+= panel-mipi-dbi.o
>  obj-$(CONFIG_DRM_SIMPLEDRM)		+= simpledrm.o
>  obj-$(CONFIG_TINYDRM_HX8357D)		+= hx8357d.o
> diff --git a/drivers/gpu/drm/tiny/ofdrm.c b/drivers/gpu/drm/tiny/ofdrm.c
> new file mode 100644
> index 000000000000..96a46078ade8
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/ofdrm.c
> @@ -0,0 +1,763 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/of_address.h>
> +#include <linux/pci.h>
> +#include <linux/platform_device.h>
> +
> +#include <drm/drm_aperture.h>
> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_state_helper.h>
> +#include <drm/drm_connector.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_device.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_fb_helper.h>
> +#include <drm/drm_format_helper.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_gem_shmem_helper.h>
> +#include <drm/drm_managed.h>
> +#include <drm/drm_modeset_helper_vtables.h>
> +#include <drm/drm_plane_helper.h>
> +#include <drm/drm_probe_helper.h>
> +#include <drm/drm_simple_kms_helper.h>
> +
> +#define DRIVER_NAME	"ofdrm"
> +#define DRIVER_DESC	"DRM driver for OF platform devices"
> +#define DRIVER_DATE	"20220501"
> +#define DRIVER_MAJOR	1
> +#define DRIVER_MINOR	0
> +
> +/*
> + * Helpers for display nodes
> + */
> +
> +static int display_get_validated_int(struct drm_device *dev, const char *name, uint32_t value)
> +{
> +	if (value > INT_MAX) {
> +		drm_err(dev, "invalid framebuffer %s of %u\n", name, value);
> +		return -EINVAL;
> +	}
> +	return (int)value;
> +}
> +
> +static int display_get_validated_int0(struct drm_device *dev, const char *name, uint32_t value)
> +{
> +	if (!value) {
> +		drm_err(dev, "invalid framebuffer %s of %u\n", name, value);
> +		return -EINVAL;
> +	}
> +	return display_get_validated_int(dev, name, value);
> +}
> +
> +static const struct drm_format_info *display_get_validated_format(struct drm_device *dev,
> +								  u32 depth)
> +{
> +	const struct drm_format_info *info;
> +	u32 format;
> +
> +	switch (depth) {
> +	case 8:
> +		format = drm_mode_legacy_fb_format(8, 8);
> +		break;
> +	case 15:
> +	case 16:
> +		format = drm_mode_legacy_fb_format(16, depth);
> +		break;
> +	case 32:
> +		format = drm_mode_legacy_fb_format(32, 24);
> +		break;
> +	default:
> +		drm_err(dev, "unsupported framebuffer depth %u\n", depth);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	info = drm_format_info(format);
> +	if (!info) {
> +		drm_err(dev, "cannot find framebuffer format for depth %u\n", depth);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	return info;
> +}
> +
> +static int display_read_u32_of(struct drm_device *dev, struct device_node *of_node,
> +			       const char *name, u32 *value)
> +{
> +	int ret = of_property_read_u32(of_node, name, value);
> +
> +	if (ret)
> +		drm_err(dev, "cannot parse framebuffer %s: error %d\n", name, ret);
> +	return ret;
> +}
> +
> +static int display_get_width_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	u32 width;
> +	int ret = display_read_u32_of(dev, of_node, "width", &width);
> +
> +	if (ret)
> +		return ret;
> +	return display_get_validated_int0(dev, "width", width);
> +}
> +
> +static int display_get_height_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	u32 height;
> +	int ret = display_read_u32_of(dev, of_node, "height", &height);
> +
> +	if (ret)
> +		return ret;
> +	return display_get_validated_int0(dev, "height", height);
> +}
> +
> +static int display_get_depth_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	u32 depth;
> +	int ret = display_read_u32_of(dev, of_node, "depth", &depth);
> +
> +	if (ret)
> +		return ret;
> +	return display_get_validated_int0(dev, "depth", depth);
> +}
> +
> +static int display_get_linebytes_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	u32 linebytes;
> +	int ret = display_read_u32_of(dev, of_node, "linebytes", &linebytes);
> +
> +	if (ret)
> +		return ret;
> +	return display_get_validated_int(dev, "linebytes", linebytes);
> +}
> +
> +static u64 display_get_address_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	u32 address;
> +	int ret;
> +
> +	/*
> +	 * Not all devices provide an address property, it's not
> +	 * a bug if this fails. The driver will try to find the
> +	 * framebuffer base address from the device's memory regions.
> +	 */
> +	ret = of_property_read_u32(of_node, "address", &address);
> +	if (ret)
> +		return OF_BAD_ADDR;
> +
> +	return address;
> +}
> +
> +/*
> + * Open Firmware display device
> + */
> +
> +struct ofdrm_device {
> +	struct drm_device dev;
> +	struct platform_device *pdev;
> +
> +	/* firmware-buffer settings */
> +	struct iosys_map screen_base;
> +	struct drm_display_mode mode;
> +	const struct drm_format_info *format;
> +	unsigned int pitch;
> +
> +	/* modesetting */
> +	uint32_t formats[8];
> +	struct drm_plane primary_plane;
> +	struct drm_crtc crtc;
> +	struct drm_encoder encoder;
> +	struct drm_connector connector;
> +};
> +
> +static struct ofdrm_device *ofdrm_device_of_dev(struct drm_device *dev)
> +{
> +	return container_of(dev, struct ofdrm_device, dev);
> +}
> +
> +/*
> + * Hardware
> + */
> +
> +#if defined(CONFIG_PCI)
> +static struct pci_dev *display_get_pci_dev_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	const __be32 *vendor_p, *device_p;
> +	u32 vendor, device;
> +	struct pci_dev *pcidev;
> +
> +	vendor_p = of_get_property(of_node, "vendor-id", NULL);
> +	if (!vendor_p)
> +		return ERR_PTR(-ENODEV);
> +	vendor = be32_to_cpup(vendor_p);
> +
> +	device_p = of_get_property(of_node, "device-id", NULL);
> +	if (!device_p)
> +		return ERR_PTR(-ENODEV);
> +	device = be32_to_cpup(device_p);
> +
> +	pcidev = pci_get_device(vendor, device, NULL);
> +	if (!pcidev)
> +		return ERR_PTR(-ENODEV);
> +
> +	return pcidev;
> +}
> +
> +static void ofdrm_pci_release(void *data)
> +{
> +	struct pci_dev *pcidev = data;
> +
> +	pci_disable_device(pcidev);
> +}
> +
> +static int ofdrm_device_init_pci(struct ofdrm_device *odev)
> +{
> +	struct drm_device *dev = &odev->dev;
> +	struct platform_device *pdev = to_platform_device(dev->dev);
> +	struct device_node *of_node = pdev->dev.of_node;
> +	struct pci_dev *pcidev;
> +	int ret;
> +
> +	/*
> +	 * Never use pcim_ or other managed helpers on the returned PCI
> +	 * device. Otherwise, probing the native driver will fail for
> +	 * resource conflicts. PCI-device management has to be tied to
> +	 * the lifetime of the platform device until the native driver
> +	 * takes over.
> +	 */
> +	pcidev = display_get_pci_dev_of(dev, of_node);
> +	if (IS_ERR(pcidev))
> +		return 0; /* no PCI device found; ignore the error */
> +
> +	ret = pci_enable_device(pcidev);
> +	if (ret) {
> +		drm_err(dev, "pci_enable_device(%s) failed: %d\n",
> +			dev_name(&pcidev->dev), ret);
> +		return ret;
> +	}
> +	ret = devm_add_action_or_reset(&pdev->dev, ofdrm_pci_release, pcidev);
> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +#else
> +static int ofdrm_device_init_pci(struct ofdrm_device *odev)
> +{
> +	return 0;
> +}
> +#endif
> +
> +/*
> + *  OF display settings
> + */
> +
> +static struct resource *ofdrm_find_fb_resource(struct ofdrm_device *odev,
> +					       struct resource *fb_res)
> +{
> +	struct platform_device *pdev = to_platform_device(odev->dev.dev);
> +	struct resource *res, *max_res = NULL;
> +	u32 i;
> +
> +	for (i = 0; pdev->num_resources; ++i) {
> +		res = platform_get_resource(pdev, IORESOURCE_MEM, i);
> +		if (!res)
> +			break; /* all resources processed */
> +		if (resource_size(res) < resource_size(fb_res))
> +			continue; /* resource too small */
> +		if (fb_res->start && resource_contains(res, fb_res))
> +			return res; /* resource contains framebuffer */
> +		if (!max_res || resource_size(res) > resource_size(max_res))
> +			max_res = res; /* store largest resource as fallback */
> +	}
> +
> +	return max_res;
> +}
> +
> +/*
> + * Modesetting
> + */
> +
> +/*
> + * Support all formats of OF display and maybe more; in order
> + * of preference. The display's update function will do any
> + * conversion necessary.
> + *
> + * TODO: Add blit helpers for remaining formats and uncomment
> + *       constants.
> + */
> +static const uint32_t ofdrm_primary_plane_formats[] = {
> +	DRM_FORMAT_XRGB8888,
> +	DRM_FORMAT_RGB565,
> +	//DRM_FORMAT_XRGB1555,
> +	//DRM_FORMAT_C8,
> +};
> +
> +static const uint64_t ofdrm_primary_plane_format_modifiers[] = {
> +	DRM_FORMAT_MOD_LINEAR,
> +	DRM_FORMAT_MOD_INVALID
> +};
> +
> +static int ofdrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
> +						   struct drm_atomic_state *new_state)
> +{
> +	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
> +	struct drm_crtc *new_crtc = new_plane_state->crtc;
> +	struct drm_crtc_state *new_crtc_state = NULL;
> +
> +	if (new_crtc)
> +		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_plane_state->crtc);
> +
> +	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
> +						   DRM_PLANE_NO_SCALING,
> +						   DRM_PLANE_NO_SCALING,
> +						   false, false);
> +}
> +
> +static void ofdrm_primary_plane_helper_atomic_update(struct drm_plane *plane,
> +						     struct drm_atomic_state *state)
> +{
> +	struct drm_device *dev = plane->dev;
> +	struct ofdrm_device *odev = ofdrm_device_of_dev(dev);
> +	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
> +	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
> +	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
> +	struct drm_framebuffer *fb = plane_state->fb;
> +	unsigned int dst_pitch = odev->pitch;
> +	const struct drm_format_info *dst_format = odev->format;
> +	struct drm_atomic_helper_damage_iter iter;
> +	struct drm_rect damage;
> +	int ret, idx;
> +
> +	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
> +	if (ret)
> +		return;
> +
> +	if (!drm_dev_enter(dev, &idx))
> +		goto out_drm_gem_fb_end_cpu_access;
> +
> +	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
> +	drm_atomic_for_each_plane_damage(&iter, &damage) {
> +		struct iosys_map dst = odev->screen_base;
> +		struct drm_rect dst_clip = plane_state->dst;
> +
> +		if (!drm_rect_intersect(&dst_clip, &damage))
> +			continue;
> +
> +		iosys_map_incr(&dst, drm_fb_clip_offset(dst_pitch, dst_format, &dst_clip));
> +		drm_fb_blit(&dst, &dst_pitch, dst_format->format, shadow_plane_state->data, fb,
> +			    &damage);
> +	}
> +
> +	drm_dev_exit(idx);
> +out_drm_gem_fb_end_cpu_access:
> +	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
> +}
> +
> +static void ofdrm_primary_plane_helper_atomic_disable(struct drm_plane *plane,
> +						      struct drm_atomic_state *state)
> +{
> +	struct drm_device *dev = plane->dev;
> +	struct ofdrm_device *odev = ofdrm_device_of_dev(dev);
> +	struct iosys_map dst = odev->screen_base;
> +	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
> +	void __iomem *dst_vmap = dst.vaddr_iomem; /* TODO: Use mapping abstraction */
> +	unsigned int dst_pitch = odev->pitch;
> +	const struct drm_format_info *dst_format = odev->format;
> +	struct drm_rect dst_clip;
> +	unsigned long lines, linepixels, i;
> +	int idx;
> +
> +	drm_rect_init(&dst_clip,
> +		      plane_state->src_x >> 16, plane_state->src_y >> 16,
> +		      plane_state->src_w >> 16, plane_state->src_h >> 16);
> +
> +	lines = drm_rect_height(&dst_clip);
> +	linepixels = drm_rect_width(&dst_clip);
> +
> +	if (!drm_dev_enter(dev, &idx))
> +		return;
> +
> +	/* Clear buffer to black if disabled */
> +	dst_vmap += drm_fb_clip_offset(dst_pitch, dst_format, &dst_clip);
> +	for (i = 0; i < lines; ++i) {
> +		memset_io(dst_vmap, 0, linepixels * dst_format->cpp[0]);
> +		dst_vmap += dst_pitch;
> +	}
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static const struct drm_plane_helper_funcs ofdrm_primary_plane_helper_funcs = {
> +	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
> +	.atomic_check = ofdrm_primary_plane_helper_atomic_check,
> +	.atomic_update = ofdrm_primary_plane_helper_atomic_update,
> +	.atomic_disable = ofdrm_primary_plane_helper_atomic_disable,
> +};
> +
> +static const struct drm_plane_funcs ofdrm_primary_plane_funcs = {
> +	.update_plane = drm_atomic_helper_update_plane,
> +	.disable_plane = drm_atomic_helper_disable_plane,
> +	.destroy = drm_plane_cleanup,
> +	DRM_GEM_SHADOW_PLANE_FUNCS,
> +};
> +
> +static enum drm_mode_status ofdrm_crtc_helper_mode_valid(struct drm_crtc *crtc,
> +							 const struct drm_display_mode *mode)
> +{
> +	struct ofdrm_device *odev = ofdrm_device_of_dev(crtc->dev);
> +
> +	return drm_crtc_helper_mode_valid_fixed(crtc, mode, &odev->mode);
> +}
> +
> +static int ofdrm_crtc_helper_atomic_check(struct drm_crtc *crtc,
> +					  struct drm_atomic_state *new_state)
> +{
> +	struct drm_crtc_state *new_crtc_state = drm_atomic_get_new_crtc_state(new_state, crtc);
> +
> +	if (!new_crtc_state->enable)
> +		return 0;
> +
> +	return drm_atomic_helper_check_crtc_primary_plane(new_crtc_state);
> +}
> +
> +/*
> + * The CRTC is always enabled. Screen updates are performed by
> + * the primary plane's atomic_update function. Disabling clears
> + * the screen in the primary plane's atomic_disable function.
> + */
> +static const struct drm_crtc_helper_funcs ofdrm_crtc_helper_funcs = {
> +	.mode_valid = ofdrm_crtc_helper_mode_valid,
> +	.atomic_check = ofdrm_crtc_helper_atomic_check,
> +};
> +
> +static const struct drm_crtc_funcs ofdrm_crtc_funcs = {
> +	.reset = drm_atomic_helper_crtc_reset,
> +	.destroy = drm_crtc_cleanup,
> +	.set_config = drm_atomic_helper_set_config,
> +	.page_flip = drm_atomic_helper_page_flip,
> +	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
> +};
> +
> +static int ofdrm_connector_helper_get_modes(struct drm_connector *connector)
> +{
> +	struct ofdrm_device *odev = ofdrm_device_of_dev(connector->dev);
> +
> +	return drm_connector_helper_get_modes_fixed(connector, &odev->mode);
> +}
> +
> +static const struct drm_connector_helper_funcs ofdrm_connector_helper_funcs = {
> +	.get_modes = ofdrm_connector_helper_get_modes,
> +};
> +
> +static const struct drm_connector_funcs ofdrm_connector_funcs = {
> +	.reset = drm_atomic_helper_connector_reset,
> +	.fill_modes = drm_helper_probe_single_connector_modes,
> +	.destroy = drm_connector_cleanup,
> +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static const struct drm_mode_config_funcs ofdrm_mode_config_funcs = {
> +	.fb_create = drm_gem_fb_create_with_dirty,
> +	.atomic_check = drm_atomic_helper_check,
> +	.atomic_commit = drm_atomic_helper_commit,
> +};
> +
> +/*
> + * Init / Cleanup
> + */
> +
> +static struct drm_display_mode ofdrm_mode(unsigned int width, unsigned int height)
> +{
> +	/*
> +	 * Assume a monitor resolution of 96 dpi to
> +	 * get a somewhat reasonable screen size.
> +	 */
> +	const struct drm_display_mode mode = {
> +		DRM_MODE_INIT(60, width, height,
> +			      DRM_MODE_RES_MM(width, 96ul),
> +			      DRM_MODE_RES_MM(height, 96ul))
> +	};
> +
> +	return mode;
> +}
> +
> +static struct ofdrm_device *ofdrm_device_create(struct drm_driver *drv,
> +						struct platform_device *pdev)
> +{
> +	struct device_node *of_node = pdev->dev.of_node;
> +	struct ofdrm_device *odev;
> +	struct drm_device *dev;
> +	int width, height, depth, linebytes;
> +	const struct drm_format_info *format;
> +	u64 address;
> +	resource_size_t fb_size, fb_base, fb_pgbase, fb_pgsize;
> +	struct resource *res, *mem;
> +	void __iomem *screen_base;
> +	struct drm_plane *primary_plane;
> +	struct drm_crtc *crtc;
> +	struct drm_encoder *encoder;
> +	struct drm_connector *connector;
> +	unsigned long max_width, max_height;
> +	size_t nformats;
> +	int ret;
> +
> +	odev = devm_drm_dev_alloc(&pdev->dev, drv, struct ofdrm_device, dev);
> +	if (IS_ERR(odev))
> +		return ERR_CAST(odev);
> +	dev = &odev->dev;
> +	platform_set_drvdata(pdev, dev);
> +
> +	ret = ofdrm_device_init_pci(odev);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	/*
> +	 * OF display-node settings
> +	 */
> +
> +	width = display_get_width_of(dev, of_node);
> +	if (width < 0)
> +		return ERR_PTR(width);
> +	height = display_get_height_of(dev, of_node);
> +	if (height < 0)
> +		return ERR_PTR(height);
> +	depth = display_get_depth_of(dev, of_node);
> +	if (depth < 0)
> +		return ERR_PTR(depth);
> +	linebytes = display_get_linebytes_of(dev, of_node);
> +	if (linebytes < 0)
> +		return ERR_PTR(linebytes);
> +
> +	format = display_get_validated_format(dev, depth);
> +	if (IS_ERR(format))
> +		return ERR_CAST(format);
> +	if (!linebytes) {
> +		linebytes = drm_format_info_min_pitch(format, 0, width);
> +		if (drm_WARN_ON(dev, !linebytes))
> +			return ERR_PTR(-EINVAL);
> +	}
> +
> +	fb_size = linebytes * height;
> +
> +	/*
> +	 * Try to figure out the address of the framebuffer. Unfortunately, Open
> +	 * Firmware doesn't provide a standard way to do so. All we can do is a
> +	 * dodgy heuristic that happens to work in practice.
> +	 *
> +	 * On most machines, the "address" property contains what we need, though
> +	 * not on Matrox cards found in IBM machines. What appears to give good
> +	 * results is to go through the PCI ranges and pick one that encloses the
> +	 * "address" property. If none match, we pick the largest.
> +	 */
> +	address = display_get_address_of(dev, of_node);
> +	if (address != OF_BAD_ADDR) {
> +		struct resource fb_res = DEFINE_RES_MEM(address, fb_size);
> +
> +		res = ofdrm_find_fb_resource(odev, &fb_res);
> +		if (!res)
> +			return ERR_PTR(-EINVAL);
> +		if (resource_contains(res, &fb_res))
> +			fb_base = address;
> +		else
> +			fb_base = res->start;
> +	} else {
> +		struct resource fb_res = DEFINE_RES_MEM(0u, fb_size);
> +
> +		res = ofdrm_find_fb_resource(odev, &fb_res);
> +		if (!res)
> +			return ERR_PTR(-EINVAL);
> +		fb_base = res->start;
> +	}
> +
> +	/*
> +	 * I/O resources
> +	 */
> +
> +	fb_pgbase = round_down(fb_base, PAGE_SIZE);
> +	fb_pgsize = fb_base - fb_pgbase + round_up(fb_size, PAGE_SIZE);
> +
> +	ret = devm_aperture_acquire_from_firmware(dev, fb_pgbase, fb_pgsize);
> +	if (ret) {
> +		drm_err(dev, "could not acquire memory range %pr: error %d\n", &res, ret);
> +		return ERR_PTR(ret);
> +	}
> +
> +	mem = devm_request_mem_region(&pdev->dev, fb_pgbase, fb_pgsize, drv->name);
> +	if (!mem) {
> +		drm_warn(dev, "could not acquire memory region %pr\n", &res);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	screen_base = devm_ioremap(&pdev->dev, mem->start, resource_size(mem));
> +	if (!screen_base)
> +		return ERR_PTR(-ENOMEM);
> +
> +	/*
> +	 * Firmware framebuffer
> +	 */
> +
> +	iosys_map_set_vaddr_iomem(&odev->screen_base, screen_base);
> +	odev->mode = ofdrm_mode(width, height);
> +	odev->format = format;
> +	odev->pitch = linebytes;
> +
> +	drm_dbg(dev, "display mode={" DRM_MODE_FMT "}\n", DRM_MODE_ARG(&odev->mode));
> +	drm_dbg(dev, "framebuffer format=%p4cc, size=%dx%d, linebytes=%d byte\n",
> +		&format->format, width, height, linebytes);
> +
> +	/*
> +	 * Mode-setting pipeline
> +	 */
> +
> +	ret = drmm_mode_config_init(dev);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	max_width = max_t(unsigned long, width, DRM_SHADOW_PLANE_MAX_WIDTH);
> +	max_height = max_t(unsigned long, height, DRM_SHADOW_PLANE_MAX_HEIGHT);
> +
> +	dev->mode_config.min_width = width;
> +	dev->mode_config.max_width = max_width;
> +	dev->mode_config.min_height = height;
> +	dev->mode_config.max_height = max_height;
> +	dev->mode_config.funcs = &ofdrm_mode_config_funcs;
> +	switch (depth) {
> +	case 32:
> +		dev->mode_config.preferred_depth = 24;
> +		break;
> +	default:
> +		dev->mode_config.preferred_depth = depth;
> +		break;
> +	}
> +
> +	/* Primary plane */
> +
> +	nformats = drm_fb_build_fourcc_list(dev, &format->format, 1,
> +					    ofdrm_primary_plane_formats,
> +					    ARRAY_SIZE(ofdrm_primary_plane_formats),
> +					    odev->formats, ARRAY_SIZE(odev->formats));
> +
> +	primary_plane = &odev->primary_plane;
> +	ret = drm_universal_plane_init(dev, primary_plane, 0, &ofdrm_primary_plane_funcs,
> +				       odev->formats, nformats,
> +				       ofdrm_primary_plane_format_modifiers,
> +				       DRM_PLANE_TYPE_PRIMARY, NULL);
> +	if (ret)
> +		return ERR_PTR(ret);
> +	drm_plane_helper_add(primary_plane, &ofdrm_primary_plane_helper_funcs);
> +	drm_plane_enable_fb_damage_clips(primary_plane);
> +
> +	/* CRTC */
> +
> +	crtc = &odev->crtc;
> +	ret = drm_crtc_init_with_planes(dev, crtc, primary_plane, NULL,
> +					&ofdrm_crtc_funcs, NULL);
> +	if (ret)
> +		return ERR_PTR(ret);
> +	drm_crtc_helper_add(crtc, &ofdrm_crtc_helper_funcs);
> +
> +	/* Encoder */
> +
> +	encoder = &odev->encoder;
> +	ret = drm_simple_encoder_init(dev, encoder, DRM_MODE_ENCODER_NONE);
> +	if (ret)
> +		return ERR_PTR(ret);
> +	encoder->possible_crtcs = drm_crtc_mask(crtc);
> +
> +	/* Connector */
> +
> +	connector = &odev->connector;
> +	ret = drm_connector_init(dev, connector, &ofdrm_connector_funcs,
> +				 DRM_MODE_CONNECTOR_Unknown);
> +	if (ret)
> +		return ERR_PTR(ret);
> +	drm_connector_helper_add(connector, &ofdrm_connector_helper_funcs);
> +	drm_connector_set_panel_orientation_with_quirk(connector,
> +						       DRM_MODE_PANEL_ORIENTATION_UNKNOWN,
> +						       width, height);
> +
> +	ret = drm_connector_attach_encoder(connector, encoder);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	drm_mode_config_reset(dev);
> +
> +	return odev;
> +}
> +
> +/*
> + * DRM driver
> + */
> +
> +DEFINE_DRM_GEM_FOPS(ofdrm_fops);
> +
> +static struct drm_driver ofdrm_driver = {
> +	DRM_GEM_SHMEM_DRIVER_OPS,
> +	.name			= DRIVER_NAME,
> +	.desc			= DRIVER_DESC,
> +	.date			= DRIVER_DATE,
> +	.major			= DRIVER_MAJOR,
> +	.minor			= DRIVER_MINOR,
> +	.driver_features	= DRIVER_ATOMIC | DRIVER_GEM | DRIVER_MODESET,
> +	.fops			= &ofdrm_fops,
> +};
> +
> +/*
> + * Platform driver
> + */
> +
> +static int ofdrm_probe(struct platform_device *pdev)
> +{
> +	struct ofdrm_device *odev;
> +	struct drm_device *dev;
> +	int ret;
> +
> +	odev = ofdrm_device_create(&ofdrm_driver, pdev);
> +	if (IS_ERR(odev))
> +		return PTR_ERR(odev);
> +	dev = &odev->dev;
> +
> +	ret = drm_dev_register(dev, 0);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * FIXME: 24-bit color depth does not work reliably with a 32-bpp
> +	 * value. Force the bpp value of the scanout buffer's format.
> +	 */
> +	drm_fbdev_generic_setup(dev, drm_format_info_bpp(odev->format, 0));
> +
> +	return 0;
> +}
> +
> +static int ofdrm_remove(struct platform_device *pdev)
> +{
> +	struct drm_device *dev = platform_get_drvdata(pdev);
> +
> +	drm_dev_unplug(dev);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id ofdrm_of_match_display[] = {
> +	{ .compatible = "display", },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, ofdrm_of_match_display);
> +
> +static struct platform_driver ofdrm_platform_driver = {
> +	.driver = {
> +		.name = "of-display",
> +		.of_match_table = ofdrm_of_match_display,
> +	},
> +	.probe = ofdrm_probe,
> +	.remove = ofdrm_remove,
> +};
> +
> +module_platform_driver(ofdrm_platform_driver);
> +
> +MODULE_DESCRIPTION(DRIVER_DESC);
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
> index cfc55273dc5d..a98987aa2784 100644
> --- a/drivers/video/fbdev/Kconfig
> +++ b/drivers/video/fbdev/Kconfig
> @@ -455,6 +455,7 @@ config FB_ATARI
>  config FB_OF
>  	bool "Open Firmware frame buffer device support"
>  	depends on (FB = y) && PPC && (!PPC_PSERIES || PCI)
> +	depends on !DRM_OFDRM

This breaks build - see
https://lore.kernel.org/linux-kbuild/CAK7LNASBhTvzkjXuJDH8ePCVXnZ=[e-mail]/

Thanks

Michal

>  	select APERTURE_HELPERS
>  	select FB_CFB_FILLRECT
>  	select FB_CFB_COPYAREA
> -- 
> 2.37.3
>

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index f07a8bf8744f..7c3bb04bd08e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6656,6 +6656,7 @@  L:	[e-mail]
 S:	Maintained
 T:	git git://anongit.freedesktop.org/drm/drm-misc
 F:	drivers/gpu/drm/drm_aperture.c
+F:	drivers/gpu/drm/tiny/ofdrm.c
 F:	drivers/gpu/drm/tiny/simpledrm.c
 F:	drivers/video/aperture.c
 F:	include/drm/drm_aperture.h
diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
index 565957264875..a300b03a3c7a 100644
--- a/drivers/gpu/drm/tiny/Kconfig
+++ b/drivers/gpu/drm/tiny/Kconfig
@@ -51,6 +51,19 @@  config DRM_GM12U320
 	 This is a KMS driver for projectors which use the GM12U320 chipset
 	 for video transfer over USB2/3, such as the Acer C120 mini projector.
 
+config DRM_OFDRM
+	tristate "Open Firmware display driver"
+	depends on DRM && OF && (PPC || COMPILE_TEST)
+	select APERTURE_HELPERS
+	select DRM_GEM_SHMEM_HELPER
+	select DRM_KMS_HELPER
+	help
+	  DRM driver for Open Firmware framebuffers.
+
+	  This driver assumes that the display hardware has been initialized
+	  by the Open Firmware before the kernel boots. Scanout buffer, size,
+	  and display format must be provided via device tree.
+
 config DRM_PANEL_MIPI_DBI
 	tristate "DRM support for MIPI DBI compatible panels"
 	depends on DRM && SPI
diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
index 1d9d6227e7ab..76dde89a044b 100644
--- a/drivers/gpu/drm/tiny/Makefile
+++ b/drivers/gpu/drm/tiny/Makefile
@@ -4,6 +4,7 @@  obj-$(CONFIG_DRM_ARCPGU)		+= arcpgu.o
 obj-$(CONFIG_DRM_BOCHS)			+= bochs.o
 obj-$(CONFIG_DRM_CIRRUS_QEMU)		+= cirrus.o
 obj-$(CONFIG_DRM_GM12U320)		+= gm12u320.o
+obj-$(CONFIG_DRM_OFDRM)			+= ofdrm.o
 obj-$(CONFIG_DRM_PANEL_MIPI_DBI)	+= panel-mipi-dbi.o
 obj-$(CONFIG_DRM_SIMPLEDRM)		+= simpledrm.o
 obj-$(CONFIG_TINYDRM_HX8357D)		+= hx8357d.o
diff --git a/drivers/gpu/drm/tiny/ofdrm.c b/drivers/gpu/drm/tiny/ofdrm.c
new file mode 100644
index 000000000000..96a46078ade8
--- /dev/null
+++ b/drivers/gpu/drm/tiny/ofdrm.c
@@ -0,0 +1,763 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/of_address.h>
+#include <linux/pci.h>
+#include <linux/platform_device.h>
+
+#include <drm/drm_aperture.h>
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_state_helper.h>
+#include <drm/drm_connector.h>
+#include <drm/drm_damage_helper.h>
+#include <drm/drm_device.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_fb_helper.h>
+#include <drm/drm_format_helper.h>
+#include <drm/drm_gem_atomic_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_managed.h>
+#include <drm/drm_modeset_helper_vtables.h>
+#include <drm/drm_plane_helper.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_simple_kms_helper.h>
+
+#define DRIVER_NAME	"ofdrm"
+#define DRIVER_DESC	"DRM driver for OF platform devices"
+#define DRIVER_DATE	"20220501"
+#define DRIVER_MAJOR	1
+#define DRIVER_MINOR	0
+
+/*
+ * Helpers for display nodes
+ */
+
+static int display_get_validated_int(struct drm_device *dev, const char *name, uint32_t value)
+{
+	if (value > INT_MAX) {
+		drm_err(dev, "invalid framebuffer %s of %u\n", name, value);
+		return -EINVAL;
+	}
+	return (int)value;
+}
+
+static int display_get_validated_int0(struct drm_device *dev, const char *name, uint32_t value)
+{
+	if (!value) {
+		drm_err(dev, "invalid framebuffer %s of %u\n", name, value);
+		return -EINVAL;
+	}
+	return display_get_validated_int(dev, name, value);
+}
+
+static const struct drm_format_info *display_get_validated_format(struct drm_device *dev,
+								  u32 depth)
+{
+	const struct drm_format_info *info;
+	u32 format;
+
+	switch (depth) {
+	case 8:
+		format = drm_mode_legacy_fb_format(8, 8);
+		break;
+	case 15:
+	case 16:
+		format = drm_mode_legacy_fb_format(16, depth);
+		break;
+	case 32:
+		format = drm_mode_legacy_fb_format(32, 24);
+		break;
+	default:
+		drm_err(dev, "unsupported framebuffer depth %u\n", depth);
+		return ERR_PTR(-EINVAL);
+	}
+
+	info = drm_format_info(format);
+	if (!info) {
+		drm_err(dev, "cannot find framebuffer format for depth %u\n", depth);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return info;
+}
+
+static int display_read_u32_of(struct drm_device *dev, struct device_node *of_node,
+			       const char *name, u32 *value)
+{
+	int ret = of_property_read_u32(of_node, name, value);
+
+	if (ret)
+		drm_err(dev, "cannot parse framebuffer %s: error %d\n", name, ret);
+	return ret;
+}
+
+static int display_get_width_of(struct drm_device *dev, struct device_node *of_node)
+{
+	u32 width;
+	int ret = display_read_u32_of(dev, of_node, "width", &width);
+
+	if (ret)
+		return ret;
+	return display_get_validated_int0(dev, "width", width);
+}
+
+static int display_get_height_of(struct drm_device *dev, struct device_node *of_node)
+{
+	u32 height;
+	int ret = display_read_u32_of(dev, of_node, "height", &height);
+
+	if (ret)
+		return ret;
+	return display_get_validated_int0(dev, "height", height);
+}
+
+static int display_get_depth_of(struct drm_device *dev, struct device_node *of_node)
+{
+	u32 depth;
+	int ret = display_read_u32_of(dev, of_node, "depth", &depth);
+
+	if (ret)
+		return ret;
+	return display_get_validated_int0(dev, "depth", depth);
+}
+
+static int display_get_linebytes_of(struct drm_device *dev, struct device_node *of_node)
+{
+	u32 linebytes;
+	int ret = display_read_u32_of(dev, of_node, "linebytes", &linebytes);
+
+	if (ret)
+		return ret;
+	return display_get_validated_int(dev, "linebytes", linebytes);
+}
+
+static u64 display_get_address_of(struct drm_device *dev, struct device_node *of_node)
+{
+	u32 address;
+	int ret;
+
+	/*
+	 * Not all devices provide an address property, it's not
+	 * a bug if this fails. The driver will try to find the
+	 * framebuffer base address from the device's memory regions.
+	 */
+	ret = of_property_read_u32(of_node, "address", &address);
+	if (ret)
+		return OF_BAD_ADDR;
+
+	return address;
+}
+
+/*
+ * Open Firmware display device
+ */
+
+struct ofdrm_device {
+	struct drm_device dev;
+	struct platform_device *pdev;
+
+	/* firmware-buffer settings */
+	struct iosys_map screen_base;
+	struct drm_display_mode mode;
+	const struct drm_format_info *format;
+	unsigned int pitch;
+
+	/* modesetting */
+	uint32_t formats[8];
+	struct drm_plane primary_plane;
+	struct drm_crtc crtc;
+	struct drm_encoder encoder;
+	struct drm_connector connector;
+};
+
+static struct ofdrm_device *ofdrm_device_of_dev(struct drm_device *dev)
+{
+	return container_of(dev, struct ofdrm_device, dev);
+}
+
+/*
+ * Hardware
+ */
+
+#if defined(CONFIG_PCI)
+static struct pci_dev *display_get_pci_dev_of(struct drm_device *dev, struct device_node *of_node)
+{
+	const __be32 *vendor_p, *device_p;
+	u32 vendor, device;
+	struct pci_dev *pcidev;
+
+	vendor_p = of_get_property(of_node, "vendor-id", NULL);
+	if (!vendor_p)
+		return ERR_PTR(-ENODEV);
+	vendor = be32_to_cpup(vendor_p);
+
+	device_p = of_get_property(of_node, "device-id", NULL);
+	if (!device_p)
+		return ERR_PTR(-ENODEV);
+	device = be32_to_cpup(device_p);
+
+	pcidev = pci_get_device(vendor, device, NULL);
+	if (!pcidev)
+		return ERR_PTR(-ENODEV);
+
+	return pcidev;
+}
+
+static void ofdrm_pci_release(void *data)
+{
+	struct pci_dev *pcidev = data;
+
+	pci_disable_device(pcidev);
+}
+
+static int ofdrm_device_init_pci(struct ofdrm_device *odev)
+{
+	struct drm_device *dev = &odev->dev;
+	struct platform_device *pdev = to_platform_device(dev->dev);
+	struct device_node *of_node = pdev->dev.of_node;
+	struct pci_dev *pcidev;
+	int ret;
+
+	/*
+	 * Never use pcim_ or other managed helpers on the returned PCI
+	 * device. Otherwise, probing the native driver will fail for
+	 * resource conflicts. PCI-device management has to be tied to
+	 * the lifetime of the platform device until the native driver
+	 * takes over.
+	 */
+	pcidev = display_get_pci_dev_of(dev, of_node);
+	if (IS_ERR(pcidev))
+		return 0; /* no PCI device found; ignore the error */
+
+	ret = pci_enable_device(pcidev);
+	if (ret) {
+		drm_err(dev, "pci_enable_device(%s) failed: %d\n",
+			dev_name(&pcidev->dev), ret);
+		return ret;
+	}
+	ret = devm_add_action_or_reset(&pdev->dev, ofdrm_pci_release, pcidev);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+#else
+static int ofdrm_device_init_pci(struct ofdrm_device *odev)
+{
+	return 0;
+}
+#endif
+
+/*
+ *  OF display settings
+ */
+
+static struct resource *ofdrm_find_fb_resource(struct ofdrm_device *odev,
+					       struct resource *fb_res)
+{
+	struct platform_device *pdev = to_platform_device(odev->dev.dev);
+	struct resource *res, *max_res = NULL;
+	u32 i;
+
+	for (i = 0; pdev->num_resources; ++i) {
+		res = platform_get_resource(pdev, IORESOURCE_MEM, i);
+		if (!res)
+			break; /* all resources processed */
+		if (resource_size(res) < resource_size(fb_res))
+			continue; /* resource too small */
+		if (fb_res->start && resource_contains(res, fb_res))
+			return res; /* resource contains framebuffer */
+		if (!max_res || resource_size(res) > resource_size(max_res))
+			max_res = res; /* store largest resource as fallback */
+	}
+
+	return max_res;
+}
+
+/*
+ * Modesetting
+ */
+
+/*
+ * Support all formats of OF display and maybe more; in order
+ * of preference. The display's update function will do any
+ * conversion necessary.
+ *
+ * TODO: Add blit helpers for remaining formats and uncomment
+ *       constants.
+ */
+static const uint32_t ofdrm_primary_plane_formats[] = {
+	DRM_FORMAT_XRGB8888,
+	DRM_FORMAT_RGB565,
+	//DRM_FORMAT_XRGB1555,
+	//DRM_FORMAT_C8,
+};
+
+static const uint64_t ofdrm_primary_plane_format_modifiers[] = {
+	DRM_FORMAT_MOD_LINEAR,
+	DRM_FORMAT_MOD_INVALID
+};
+
+static int ofdrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
+						   struct drm_atomic_state *new_state)
+{
+	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
+	struct drm_crtc *new_crtc = new_plane_state->crtc;
+	struct drm_crtc_state *new_crtc_state = NULL;
+
+	if (new_crtc)
+		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_plane_state->crtc);
+
+	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
+						   DRM_PLANE_NO_SCALING,
+						   DRM_PLANE_NO_SCALING,
+						   false, false);
+}
+
+static void ofdrm_primary_plane_helper_atomic_update(struct drm_plane *plane,
+						     struct drm_atomic_state *state)
+{
+	struct drm_device *dev = plane->dev;
+	struct ofdrm_device *odev = ofdrm_device_of_dev(dev);
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
+	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
+	struct drm_framebuffer *fb = plane_state->fb;
+	unsigned int dst_pitch = odev->pitch;
+	const struct drm_format_info *dst_format = odev->format;
+	struct drm_atomic_helper_damage_iter iter;
+	struct drm_rect damage;
+	int ret, idx;
+
+	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
+	if (ret)
+		return;
+
+	if (!drm_dev_enter(dev, &idx))
+		goto out_drm_gem_fb_end_cpu_access;
+
+	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
+	drm_atomic_for_each_plane_damage(&iter, &damage) {
+		struct iosys_map dst = odev->screen_base;
+		struct drm_rect dst_clip = plane_state->dst;
+
+		if (!drm_rect_intersect(&dst_clip, &damage))
+			continue;
+
+		iosys_map_incr(&dst, drm_fb_clip_offset(dst_pitch, dst_format, &dst_clip));
+		drm_fb_blit(&dst, &dst_pitch, dst_format->format, shadow_plane_state->data, fb,
+			    &damage);
+	}
+
+	drm_dev_exit(idx);
+out_drm_gem_fb_end_cpu_access:
+	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
+}
+
+static void ofdrm_primary_plane_helper_atomic_disable(struct drm_plane *plane,
+						      struct drm_atomic_state *state)
+{
+	struct drm_device *dev = plane->dev;
+	struct ofdrm_device *odev = ofdrm_device_of_dev(dev);
+	struct iosys_map dst = odev->screen_base;
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+	void __iomem *dst_vmap = dst.vaddr_iomem; /* TODO: Use mapping abstraction */
+	unsigned int dst_pitch = odev->pitch;
+	const struct drm_format_info *dst_format = odev->format;
+	struct drm_rect dst_clip;
+	unsigned long lines, linepixels, i;
+	int idx;
+
+	drm_rect_init(&dst_clip,
+		      plane_state->src_x >> 16, plane_state->src_y >> 16,
+		      plane_state->src_w >> 16, plane_state->src_h >> 16);
+
+	lines = drm_rect_height(&dst_clip);
+	linepixels = drm_rect_width(&dst_clip);
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
+
+	/* Clear buffer to black if disabled */
+	dst_vmap += drm_fb_clip_offset(dst_pitch, dst_format, &dst_clip);
+	for (i = 0; i < lines; ++i) {
+		memset_io(dst_vmap, 0, linepixels * dst_format->cpp[0]);
+		dst_vmap += dst_pitch;
+	}
+
+	drm_dev_exit(idx);
+}
+
+static const struct drm_plane_helper_funcs ofdrm_primary_plane_helper_funcs = {
+	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
+	.atomic_check = ofdrm_primary_plane_helper_atomic_check,
+	.atomic_update = ofdrm_primary_plane_helper_atomic_update,
+	.atomic_disable = ofdrm_primary_plane_helper_atomic_disable,
+};
+
+static const struct drm_plane_funcs ofdrm_primary_plane_funcs = {
+	.update_plane = drm_atomic_helper_update_plane,
+	.disable_plane = drm_atomic_helper_disable_plane,
+	.destroy = drm_plane_cleanup,
+	DRM_GEM_SHADOW_PLANE_FUNCS,
+};
+
+static enum drm_mode_status ofdrm_crtc_helper_mode_valid(struct drm_crtc *crtc,
+							 const struct drm_display_mode *mode)
+{
+	struct ofdrm_device *odev = ofdrm_device_of_dev(crtc->dev);
+
+	return drm_crtc_helper_mode_valid_fixed(crtc, mode, &odev->mode);
+}
+
+static int ofdrm_crtc_helper_atomic_check(struct drm_crtc *crtc,
+					  struct drm_atomic_state *new_state)
+{
+	struct drm_crtc_state *new_crtc_state = drm_atomic_get_new_crtc_state(new_state, crtc);
+
+	if (!new_crtc_state->enable)
+		return 0;
+
+	return drm_atomic_helper_check_crtc_primary_plane(new_crtc_state);
+}
+
+/*
+ * The CRTC is always enabled. Screen updates are performed by
+ * the primary plane's atomic_update function. Disabling clears
+ * the screen in the primary plane's atomic_disable function.
+ */
+static const struct drm_crtc_helper_funcs ofdrm_crtc_helper_funcs = {
+	.mode_valid = ofdrm_crtc_helper_mode_valid,
+	.atomic_check = ofdrm_crtc_helper_atomic_check,
+};
+
+static const struct drm_crtc_funcs ofdrm_crtc_funcs = {
+	.reset = drm_atomic_helper_crtc_reset,
+	.destroy = drm_crtc_cleanup,
+	.set_config = drm_atomic_helper_set_config,
+	.page_flip = drm_atomic_helper_page_flip,
+	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+};
+
+static int ofdrm_connector_helper_get_modes(struct drm_connector *connector)
+{
+	struct ofdrm_device *odev = ofdrm_device_of_dev(connector->dev);
+
+	return drm_connector_helper_get_modes_fixed(connector, &odev->mode);
+}
+
+static const struct drm_connector_helper_funcs ofdrm_connector_helper_funcs = {
+	.get_modes = ofdrm_connector_helper_get_modes,
+};
+
+static const struct drm_connector_funcs ofdrm_connector_funcs = {
+	.reset = drm_atomic_helper_connector_reset,
+	.fill_modes = drm_helper_probe_single_connector_modes,
+	.destroy = drm_connector_cleanup,
+	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
+};
+
+static const struct drm_mode_config_funcs ofdrm_mode_config_funcs = {
+	.fb_create = drm_gem_fb_create_with_dirty,
+	.atomic_check = drm_atomic_helper_check,
+	.atomic_commit = drm_atomic_helper_commit,
+};
+
+/*
+ * Init / Cleanup
+ */
+
+static struct drm_display_mode ofdrm_mode(unsigned int width, unsigned int height)
+{
+	/*
+	 * Assume a monitor resolution of 96 dpi to
+	 * get a somewhat reasonable screen size.
+	 */
+	const struct drm_display_mode mode = {
+		DRM_MODE_INIT(60, width, height,
+			      DRM_MODE_RES_MM(width, 96ul),
+			      DRM_MODE_RES_MM(height, 96ul))
+	};
+
+	return mode;
+}
+
+static struct ofdrm_device *ofdrm_device_create(struct drm_driver *drv,
+						struct platform_device *pdev)
+{
+	struct device_node *of_node = pdev->dev.of_node;
+	struct ofdrm_device *odev;
+	struct drm_device *dev;
+	int width, height, depth, linebytes;
+	const struct drm_format_info *format;
+	u64 address;
+	resource_size_t fb_size, fb_base, fb_pgbase, fb_pgsize;
+	struct resource *res, *mem;
+	void __iomem *screen_base;
+	struct drm_plane *primary_plane;
+	struct drm_crtc *crtc;
+	struct drm_encoder *encoder;
+	struct drm_connector *connector;
+	unsigned long max_width, max_height;
+	size_t nformats;
+	int ret;
+
+	odev = devm_drm_dev_alloc(&pdev->dev, drv, struct ofdrm_device, dev);
+	if (IS_ERR(odev))
+		return ERR_CAST(odev);
+	dev = &odev->dev;
+	platform_set_drvdata(pdev, dev);
+
+	ret = ofdrm_device_init_pci(odev);
+	if (ret)
+		return ERR_PTR(ret);
+
+	/*
+	 * OF display-node settings
+	 */
+
+	width = display_get_width_of(dev, of_node);
+	if (width < 0)
+		return ERR_PTR(width);
+	height = display_get_height_of(dev, of_node);
+	if (height < 0)
+		return ERR_PTR(height);
+	depth = display_get_depth_of(dev, of_node);
+	if (depth < 0)
+		return ERR_PTR(depth);
+	linebytes = display_get_linebytes_of(dev, of_node);
+	if (linebytes < 0)
+		return ERR_PTR(linebytes);
+
+	format = display_get_validated_format(dev, depth);
+	if (IS_ERR(format))
+		return ERR_CAST(format);
+	if (!linebytes) {
+		linebytes = drm_format_info_min_pitch(format, 0, width);
+		if (drm_WARN_ON(dev, !linebytes))
+			return ERR_PTR(-EINVAL);
+	}
+
+	fb_size = linebytes * height;
+
+	/*
+	 * Try to figure out the address of the framebuffer. Unfortunately, Open
+	 * Firmware doesn't provide a standard way to do so. All we can do is a
+	 * dodgy heuristic that happens to work in practice.
+	 *
+	 * On most machines, the "address" property contains what we need, though
+	 * not on Matrox cards found in IBM machines. What appears to give good
+	 * results is to go through the PCI ranges and pick one that encloses the
+	 * "address" property. If none match, we pick the largest.
+	 */
+	address = display_get_address_of(dev, of_node);
+	if (address != OF_BAD_ADDR) {
+		struct resource fb_res = DEFINE_RES_MEM(address, fb_size);
+
+		res = ofdrm_find_fb_resource(odev, &fb_res);
+		if (!res)
+			return ERR_PTR(-EINVAL);
+		if (resource_contains(res, &fb_res))
+			fb_base = address;
+		else
+			fb_base = res->start;
+	} else {
+		struct resource fb_res = DEFINE_RES_MEM(0u, fb_size);
+
+		res = ofdrm_find_fb_resource(odev, &fb_res);
+		if (!res)
+			return ERR_PTR(-EINVAL);
+		fb_base = res->start;
+	}
+
+	/*
+	 * I/O resources
+	 */
+
+	fb_pgbase = round_down(fb_base, PAGE_SIZE);
+	fb_pgsize = fb_base - fb_pgbase + round_up(fb_size, PAGE_SIZE);
+
+	ret = devm_aperture_acquire_from_firmware(dev, fb_pgbase, fb_pgsize);
+	if (ret) {
+		drm_err(dev, "could not acquire memory range %pr: error %d\n", &res, ret);
+		return ERR_PTR(ret);
+	}
+
+	mem = devm_request_mem_region(&pdev->dev, fb_pgbase, fb_pgsize, drv->name);
+	if (!mem) {
+		drm_warn(dev, "could not acquire memory region %pr\n", &res);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	screen_base = devm_ioremap(&pdev->dev, mem->start, resource_size(mem));
+	if (!screen_base)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * Firmware framebuffer
+	 */
+
+	iosys_map_set_vaddr_iomem(&odev->screen_base, screen_base);
+	odev->mode = ofdrm_mode(width, height);
+	odev->format = format;
+	odev->pitch = linebytes;
+
+	drm_dbg(dev, "display mode={" DRM_MODE_FMT "}\n", DRM_MODE_ARG(&odev->mode));
+	drm_dbg(dev, "framebuffer format=%p4cc, size=%dx%d, linebytes=%d byte\n",
+		&format->format, width, height, linebytes);
+
+	/*
+	 * Mode-setting pipeline
+	 */
+
+	ret = drmm_mode_config_init(dev);
+	if (ret)
+		return ERR_PTR(ret);
+
+	max_width = max_t(unsigned long, width, DRM_SHADOW_PLANE_MAX_WIDTH);
+	max_height = max_t(unsigned long, height, DRM_SHADOW_PLANE_MAX_HEIGHT);
+
+	dev->mode_config.min_width = width;
+	dev->mode_config.max_width = max_width;
+	dev->mode_config.min_height = height;
+	dev->mode_config.max_height = max_height;
+	dev->mode_config.funcs = &ofdrm_mode_config_funcs;
+	switch (depth) {
+	case 32:
+		dev->mode_config.preferred_depth = 24;
+		break;
+	default:
+		dev->mode_config.preferred_depth = depth;
+		break;
+	}
+
+	/* Primary plane */
+
+	nformats = drm_fb_build_fourcc_list(dev, &format->format, 1,
+					    ofdrm_primary_plane_formats,
+					    ARRAY_SIZE(ofdrm_primary_plane_formats),
+					    odev->formats, ARRAY_SIZE(odev->formats));
+
+	primary_plane = &odev->primary_plane;
+	ret = drm_universal_plane_init(dev, primary_plane, 0, &ofdrm_primary_plane_funcs,
+				       odev->formats, nformats,
+				       ofdrm_primary_plane_format_modifiers,
+				       DRM_PLANE_TYPE_PRIMARY, NULL);
+	if (ret)
+		return ERR_PTR(ret);
+	drm_plane_helper_add(primary_plane, &ofdrm_primary_plane_helper_funcs);
+	drm_plane_enable_fb_damage_clips(primary_plane);
+
+	/* CRTC */
+
+	crtc = &odev->crtc;
+	ret = drm_crtc_init_with_planes(dev, crtc, primary_plane, NULL,
+					&ofdrm_crtc_funcs, NULL);
+	if (ret)
+		return ERR_PTR(ret);
+	drm_crtc_helper_add(crtc, &ofdrm_crtc_helper_funcs);
+
+	/* Encoder */
+
+	encoder = &odev->encoder;
+	ret = drm_simple_encoder_init(dev, encoder, DRM_MODE_ENCODER_NONE);
+	if (ret)
+		return ERR_PTR(ret);
+	encoder->possible_crtcs = drm_crtc_mask(crtc);
+
+	/* Connector */
+
+	connector = &odev->connector;
+	ret = drm_connector_init(dev, connector, &ofdrm_connector_funcs,
+				 DRM_MODE_CONNECTOR_Unknown);
+	if (ret)
+		return ERR_PTR(ret);
+	drm_connector_helper_add(connector, &ofdrm_connector_helper_funcs);
+	drm_connector_set_panel_orientation_with_quirk(connector,
+						       DRM_MODE_PANEL_ORIENTATION_UNKNOWN,
+						       width, height);
+
+	ret = drm_connector_attach_encoder(connector, encoder);
+	if (ret)
+		return ERR_PTR(ret);
+
+	drm_mode_config_reset(dev);
+
+	return odev;
+}
+
+/*
+ * DRM driver
+ */
+
+DEFINE_DRM_GEM_FOPS(ofdrm_fops);
+
+static struct drm_driver ofdrm_driver = {
+	DRM_GEM_SHMEM_DRIVER_OPS,
+	.name			= DRIVER_NAME,
+	.desc			= DRIVER_DESC,
+	.date			= DRIVER_DATE,
+	.major			= DRIVER_MAJOR,
+	.minor			= DRIVER_MINOR,
+	.driver_features	= DRIVER_ATOMIC | DRIVER_GEM | DRIVER_MODESET,
+	.fops			= &ofdrm_fops,
+};
+
+/*
+ * Platform driver
+ */
+
+static int ofdrm_probe(struct platform_device *pdev)
+{
+	struct ofdrm_device *odev;
+	struct drm_device *dev;
+	int ret;
+
+	odev = ofdrm_device_create(&ofdrm_driver, pdev);
+	if (IS_ERR(odev))
+		return PTR_ERR(odev);
+	dev = &odev->dev;
+
+	ret = drm_dev_register(dev, 0);
+	if (ret)
+		return ret;
+
+	/*
+	 * FIXME: 24-bit color depth does not work reliably with a 32-bpp
+	 * value. Force the bpp value of the scanout buffer's format.
+	 */
+	drm_fbdev_generic_setup(dev, drm_format_info_bpp(odev->format, 0));
+
+	return 0;
+}
+
+static int ofdrm_remove(struct platform_device *pdev)
+{
+	struct drm_device *dev = platform_get_drvdata(pdev);
+
+	drm_dev_unplug(dev);
+
+	return 0;
+}
+
+static const struct of_device_id ofdrm_of_match_display[] = {
+	{ .compatible = "display", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ofdrm_of_match_display);
+
+static struct platform_driver ofdrm_platform_driver = {
+	.driver = {
+		.name = "of-display",
+		.of_match_table = ofdrm_of_match_display,
+	},
+	.probe = ofdrm_probe,
+	.remove = ofdrm_remove,
+};
+
+module_platform_driver(ofdrm_platform_driver);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
index cfc55273dc5d..a98987aa2784 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -455,6 +455,7 @@  config FB_ATARI
 config FB_OF
 	bool "Open Firmware frame buffer device support"
 	depends on (FB = y) && PPC && (!PPC_PSERIES || PCI)
+	depends on !DRM_OFDRM
 	select APERTURE_HELPERS
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA