[PATCH drm 0/6] PRIME Synchronization

[Alex Goins]

Hello all,

For a while now, I've been working to fix tearing with PRIME. I have a working
solution that requires changes to DRM, libdrm, and the X server. I've also
implemented sink support in the modesetting driver, and source support in the
NVIDIA proprietary driver.

These DRM patches ultimately provide a new ioctl, DRM_IOCTL_PRIME_PAGE_FLIP,
that sets up a fence on a PRIME member's DMA-BUF reservation object with a
callback to schedule a flip to the associated fb.

With my synchronization patches to X, it is possible to export two shared
buffers per crtc instead of just one. The sink driver uses
DRM_IOCTL_PRIME_PAGE_FLIP to set up fences on each of these buffers. When the
source driver is done presenting on a given buffer, it signals the associated
fence, and the sink flips on the next vblank. In the page flip event handler,
the sink driver uses the ioctl to set up another fence, and explicitly requests
a present on the current back buffer using a new function in the X ABI. Thus,
flips are driven by presents, presents are driven by flips, and the whole thing
conforms to the sink's refresh rate.

Right now, the part that signals the fence is a vendor-specific ioctl, but I'm
open to factoring it out into a core DRM ioctl and DRM driver function helper
like DRM_IOCTL_PRIME_PAGE_FLIP if it would make implementing source support
easier for open source drivers.

Due to the lack of asynchronous atomic modesetting support on i915 (the sink of
most hybrid graphics systems,) I've implemented this on top of the old page_flip
method. Perhaps an atomic modesetting / nuclear pageflip based method would be
better, but it wouldn't be as viable without widespread asynchronous support.
I'm willing to implement an atomic modesetting version if required, but it's
less clear what the best implementation would be: perhaps a fence property that
defers asynchronous commits. There are enough ways to do it that it probably
warrants prior discussion. Nonetheless, this method is necessary at least as a
fallback until i915 supports asynchronous atomic modesetting.

To give some greater context, I've uploaded my branches for DRM, libdrm, and the
X server to Github. I'll move forward with upstreaming the libdrm and X changes
if and when these DRM patches go in.

DRM Tree:    https://github.com/GoinsWithTheWind/drm-prime-sync
libdrm Tree: https://github.com/GoinsWithTheWind/libdrm-prime-sync
X Tree:      https://github.com/GoinsWithTheWind/xserver-prime-sync

Thanks,
Alex @ NVIDIA Linux Driver Team

agoins (6):
  drm: factor out drm_mode_page_flip_ioctl()
  drm: generalize drm_prime_lookup
  drm: add fence context
  drm: add drm_gem_prime_page_flip() helper
  drm: add prime_page_flip() driver function
  drm: add DRM_IOCTL_PRIME_PAGE_FLIP

 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c     |   1 +
 drivers/gpu/drm/armada/armada_drv.c         |   1 +
 drivers/gpu/drm/drm_crtc.c                  |  90 ++++++++----
 drivers/gpu/drm/drm_internal.h              |   2 +
 drivers/gpu/drm/drm_ioctl.c                 |   1 +
 drivers/gpu/drm/drm_prime.c                 | 213 ++++++++++++++++++++++++++--
 drivers/gpu/drm/exynos/exynos_drm_drv.c     |   1 +
 drivers/gpu/drm/i915/i915_drv.c             |   1 +
 drivers/gpu/drm/imx/imx-drm-core.c          |   1 +
 drivers/gpu/drm/msm/msm_drv.c               |   1 +
 drivers/gpu/drm/nouveau/nouveau_drm.c       |   1 +
 drivers/gpu/drm/omapdrm/omap_drv.c          |   1 +
 drivers/gpu/drm/qxl/qxl_drv.c               |   1 +
 drivers/gpu/drm/radeon/radeon_drv.c         |   1 +
 drivers/gpu/drm/rcar-du/rcar_du_drv.c       |   1 +
 drivers/gpu/drm/rockchip/rockchip_drm_drv.c |   1 +
 drivers/gpu/drm/shmobile/shmob_drm_drv.c    |   1 +
 drivers/gpu/drm/sti/sti_drv.c               |   1 +
 drivers/gpu/drm/tegra/drm.c                 |   1 +
 drivers/gpu/drm/udl/udl_drv.c               |   1 +
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c         |   1 +
 include/drm/drmP.h                          |   8 ++
 include/drm/drm_crtc.h                      |   4 +
 include/uapi/drm/drm.h                      |  10 ++
 24 files changed, 303 insertions(+), 42 deletions(-)

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1.9.1