Specify how the atomic state is maintained between userspace and kernel, plus the special case for async flips. Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx> --- v4: new patch --- Documentation/gpu/drm-uapi.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 65fb3036a580..5464376051cc 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -486,3 +486,22 @@ and the CRTC index is its position in this array. .. kernel-doc:: include/uapi/drm/drm_mode.h :internal: + +KMS atomic state +================ + +If a userspace using the DRM atomic API would like to change the modeset, it +needs to do in an atomic way, changing all desired properties in a single +commit. Following commits may contain the same properties again, as if they were +new. The kernel can then judge if those properties requires modesetting and real +changes, or it's just the same state as before. In summary, userspace commits do +not need to set the minimal state as possible and can commit redundant +information, and the kernel will ignore it. + +An observation must be made for atomic operations with DRM_MODE_PAGE_FLIP_ASYNC. +In such scenarios properties values can be sent, but the if they change +something, the kernel will reject the flip. This is done because property +changes can lead to modesetting, that would defeat the goal of flipping as fast +as possible. The only exceptions are the framebuffer ID to be flipped to and +mode IDs changes, which could be referring to an identical mode, thus not +requiring modeset. -- 2.41.0