| Message ID | 20250307080836.42848-1-tzimmermann@suse.de (mailing list archive) |
|---|---|
| Headers | show |
| Series | drm: Provide a dedicated DMA device for PRIME import | expand |
On Fri, 07 Mar 2025, Thomas Zimmermann <tzimmermann@suse.de> wrote: > Importing dma-bufs via PRIME requires a DMA-capable hardware device. > This is not the case for USB, where DMA is performed entirely by the > USB controller instead of the USB devices. > > Drivers for USB-based hardware maintain their own workarounds for this > problem. The original idea to resolve this was to provide different > PRIME helpers for such devices, but the dma-buf code internally assumes > DMA functionality as well. So that ideas is not realistic. > > Let's instead turn the current workaround into a feature. Patch 1 adds a > dma_dev field to struct drm_device and makes the PRIME code use it. Patches > 2 to 5 replace related driver code. > > It will also be useful in other code. The exynos and mediatek drivers > already maintain a dedicated DMA device for non-PRIME code. They could > likely use dma_dev as well. GEM-DMA helpers currently allocate DMA > memory with the regular parent device. They should support the dma_dev > settings as well. > > Tested with udl. I mainly reviewed the first patch, but then glanced through all the rest too, and didn't spot anything obviously wrong. So FWIW, Reviewed-by: Jani Nikula <jani.nikula@intel.com> on the rest too. > > v2: > - maintain reference on dma_dev (Jani) > - improve docs (Maxime) > - update appletbdrm > > Thomas Zimmermann (5): > drm/prime: Support dedicated DMA device for dma-buf imports > drm/appletbdrm: Set struct drm_device.dma_dev > drm/gm12u320: Set struct drm_device.dma_dev > drm/gud: Set struct drm_device.dma_dev > drm/udl: Set struct drm_device.dma_dev > > drivers/gpu/drm/drm_drv.c | 21 ++++++++++++++ > drivers/gpu/drm/drm_prime.c | 2 +- > drivers/gpu/drm/gud/gud_drv.c | 33 ++++++--------------- > drivers/gpu/drm/gud/gud_internal.h | 1 - > drivers/gpu/drm/tiny/appletbdrm.c | 27 +++++++----------- > drivers/gpu/drm/tiny/gm12u320.c | 46 +++++++++--------------------- > drivers/gpu/drm/udl/udl_drv.c | 17 ----------- > drivers/gpu/drm/udl/udl_drv.h | 1 - > drivers/gpu/drm/udl/udl_main.c | 14 ++++----- > include/drm/drm_device.h | 41 ++++++++++++++++++++++++++ > 10 files changed, 102 insertions(+), 101 deletions(-)
On Fri, Mar 07, 2025 at 09:03:58AM +0100, Thomas Zimmermann wrote: > Importing dma-bufs via PRIME requires a DMA-capable hardware device. > This is not the case for USB, where DMA is performed entirely by the > USB controller instead of the USB devices. > > Drivers for USB-based hardware maintain their own workarounds for this > problem. The original idea to resolve this was to provide different > PRIME helpers for such devices, but the dma-buf code internally assumes > DMA functionality as well. So that ideas is not realistic. So dma-buf without dma is doable, but you have to avoid dma_buf_attach. And that is a lot of surgery in the current prime helpers, since those assume that an attachment always exists. But dma-buf itself is entirely fine with cpu-only access through either userspace mmap or kernel vmap. I think as an interim step this is still good, since it makes the current hacks easier to find because at least it's all common now. -Sima > Let's instead turn the current workaround into a feature. Patch 1 adds a > dma_dev field to struct drm_device and makes the PRIME code use it. Patches > 2 to 5 replace related driver code. > > It will also be useful in other code. The exynos and mediatek drivers > already maintain a dedicated DMA device for non-PRIME code. They could > likely use dma_dev as well. GEM-DMA helpers currently allocate DMA > memory with the regular parent device. They should support the dma_dev > settings as well. > > Tested with udl. > > v2: > - maintain reference on dma_dev (Jani) > - improve docs (Maxime) > - update appletbdrm > > Thomas Zimmermann (5): > drm/prime: Support dedicated DMA device for dma-buf imports > drm/appletbdrm: Set struct drm_device.dma_dev > drm/gm12u320: Set struct drm_device.dma_dev > drm/gud: Set struct drm_device.dma_dev > drm/udl: Set struct drm_device.dma_dev > > drivers/gpu/drm/drm_drv.c | 21 ++++++++++++++ > drivers/gpu/drm/drm_prime.c | 2 +- > drivers/gpu/drm/gud/gud_drv.c | 33 ++++++--------------- > drivers/gpu/drm/gud/gud_internal.h | 1 - > drivers/gpu/drm/tiny/appletbdrm.c | 27 +++++++----------- > drivers/gpu/drm/tiny/gm12u320.c | 46 +++++++++--------------------- > drivers/gpu/drm/udl/udl_drv.c | 17 ----------- > drivers/gpu/drm/udl/udl_drv.h | 1 - > drivers/gpu/drm/udl/udl_main.c | 14 ++++----- > include/drm/drm_device.h | 41 ++++++++++++++++++++++++++ > 10 files changed, 102 insertions(+), 101 deletions(-) > > -- > 2.48.1 >