[v2,12/18] drm/sysfb: ofdrm: Add EDID support

Commit Message

Thomas Zimmermann March 31, 2025, 3:52 p.m. UTC

Add EDID support to sysfb connector helpers. Read the EDID property
from the OF node in ofdrm. Without EDID, this does nothing.

Some systems with OF display, such as 32-bit PPC Macintoshs, provide
the system display's EDID data as node property in their DT. Exporting
this information allows compositors to implement correct DPI and
meaningful color management.

v2:
- return errno codes on errors (Jani)
- simplify EDID read logic (Jani)

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
---
 drivers/gpu/drm/sysfb/drm_sysfb_helper.c | 25 ++++++++++++++++++++++++
 drivers/gpu/drm/sysfb/drm_sysfb_helper.h |  2 ++
 drivers/gpu/drm/sysfb/ofdrm.c            | 20 +++++++++++++++++++
 3 files changed, 47 insertions(+)

Patch

diff --git a/drivers/gpu/drm/sysfb/drm_sysfb_helper.c b/drivers/gpu/drm/sysfb/drm_sysfb_helper.c
index b48e06b253051..1971d7e171f81 100644
--- a/drivers/gpu/drm/sysfb/drm_sysfb_helper.c
+++ b/drivers/gpu/drm/sysfb/drm_sysfb_helper.c
@@ -9,6 +9,7 @@ 
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>
 #include <drm/drm_gem_atomic_helper.h>
@@ -281,10 +282,34 @@  EXPORT_SYMBOL(drm_sysfb_crtc_atomic_destroy_state);
  * Connector
  */
 
+static int drm_sysfb_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
+{
+	struct drm_sysfb_device *sysfb = data;
+	const u8 *edid = sysfb->edid;
+	size_t off = block * EDID_LENGTH;
+	size_t end = off + len;
+
+	if (!edid)
+		return -EINVAL;
+	if (end > EDID_LENGTH)
+		return -EINVAL;
+	memcpy(buf, &edid[off], len);
+
+	return 0;
+}
+
 int drm_sysfb_connector_helper_get_modes(struct drm_connector *connector)
 {
 	struct drm_sysfb_device *sysfb = to_drm_sysfb_device(connector->dev);
+	const struct drm_edid *drm_edid;
+
+	if (sysfb->edid) {
+		drm_edid = drm_edid_read_custom(connector, drm_sysfb_get_edid_block, sysfb);
+		drm_edid_connector_update(connector, drm_edid);
+		drm_edid_free(drm_edid);
+	}
 
+	/* Return the fixed mode even with EDID */
 	return drm_connector_helper_get_modes_fixed(connector, &sysfb->fb_mode);
 }
 EXPORT_SYMBOL(drm_sysfb_connector_helper_get_modes);
diff --git a/drivers/gpu/drm/sysfb/drm_sysfb_helper.h b/drivers/gpu/drm/sysfb/drm_sysfb_helper.h
index 45e396bf74b73..3684bd0ef0853 100644
--- a/drivers/gpu/drm/sysfb/drm_sysfb_helper.h
+++ b/drivers/gpu/drm/sysfb/drm_sysfb_helper.h
@@ -24,6 +24,8 @@  struct drm_display_mode drm_sysfb_mode(unsigned int width,
 struct drm_sysfb_device {
 	struct drm_device dev;
 
+	const u8 *edid; /* can be NULL */
+
 	/* hardware settings */
 	struct drm_display_mode fb_mode;
 	const struct drm_format_info *fb_format;
diff --git a/drivers/gpu/drm/sysfb/ofdrm.c b/drivers/gpu/drm/sysfb/ofdrm.c
index 71e661ba93299..86c1a0c80ceb3 100644
--- a/drivers/gpu/drm/sysfb/ofdrm.c
+++ b/drivers/gpu/drm/sysfb/ofdrm.c
@@ -12,6 +12,7 @@ 
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_device.h>
 #include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
 #include <drm/drm_fbdev_shmem.h>
 #include <drm/drm_format_helper.h>
 #include <drm/drm_framebuffer.h>
@@ -227,6 +228,16 @@  static u64 display_get_address_of(struct drm_device *dev, struct device_node *of
 	return address;
 }
 
+static const u8 *display_get_edid_of(struct drm_device *dev, struct device_node *of_node,
+				     u8 buf[EDID_LENGTH])
+{
+	int ret = of_property_read_u8_array(of_node, "EDID", buf, EDID_LENGTH);
+
+	if (ret)
+		return NULL;
+	return buf;
+}
+
 static bool is_avivo(u32 vendor, u32 device)
 {
 	/* This will match most R5xx */
@@ -298,6 +309,8 @@  struct ofdrm_device {
 	/* colormap */
 	void __iomem *cmap_base;
 
+	u8 edid[EDID_LENGTH];
+
 	/* modesetting */
 	u32 formats[DRM_SYSFB_PLANE_NFORMATS(1)];
 	struct drm_plane primary_plane;
@@ -840,6 +853,7 @@  static struct ofdrm_device *ofdrm_device_create(struct drm_driver *drv,
 	int width, height, depth, linebytes;
 	const struct drm_format_info *format;
 	u64 address;
+	const u8 *edid;
 	resource_size_t fb_size, fb_base, fb_pgbase, fb_pgsize;
 	struct resource *res, *mem;
 	void __iomem *screen_base;
@@ -989,6 +1003,9 @@  static struct ofdrm_device *ofdrm_device_create(struct drm_driver *drv,
 		}
 	}
 
+	/* EDID is optional */
+	edid = display_get_edid_of(dev, of_node, odev->edid);
+
 	/*
 	 * Firmware framebuffer
 	 */
@@ -999,6 +1016,7 @@  static struct ofdrm_device *ofdrm_device_create(struct drm_driver *drv,
 	sysfb->fb_pitch = linebytes;
 	if (odev->cmap_base)
 		sysfb->fb_gamma_lut_size = OFDRM_GAMMA_LUT_SIZE;
+	sysfb->edid = edid;
 
 	drm_dbg(dev, "display mode={" DRM_MODE_FMT "}\n", DRM_MODE_ARG(&sysfb->fb_mode));
 	drm_dbg(dev, "framebuffer format=%p4cc, size=%dx%d, linebytes=%d byte\n",
@@ -1072,6 +1090,8 @@  static struct ofdrm_device *ofdrm_device_create(struct drm_driver *drv,
 	drm_connector_set_panel_orientation_with_quirk(connector,
 						       DRM_MODE_PANEL_ORIENTATION_UNKNOWN,
 						       width, height);
+	if (edid)
+		drm_connector_attach_edid_property(connector);
 
 	ret = drm_connector_attach_encoder(connector, encoder);
 	if (ret)