Hi Am 15.11.23 um 14:15 schrieb Javier Martinez Canillas:
The "Damage Tracking Properties" section in the documentation doesn't have info about the two type of damage handling: frame damage vs buffer damage. Add it to the section and mention that helpers only support frame damage, and how drivers handling buffer damage can indicate that the damage clips should be ignored. Also add references to further documentation about the two damage types. Suggested-by: Simon Ser <contact@xxxxxxxxxxx> Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx> --- - Dropped Simon Ser's Reviwed-by tag because the text changed to adapt to the approach Thomas Zimmermann suggested for v2. (no changes since v1) drivers/gpu/drm/drm_plane.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c index 24e7998d1731..3b1b8bca3065 100644 --- a/drivers/gpu/drm/drm_plane.c +++ b/drivers/gpu/drm/drm_plane.c @@ -1442,6 +1442,26 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev, * Drivers implementing damage can use drm_atomic_helper_damage_iter_init() and * drm_atomic_helper_damage_iter_next() helper iterator function to get damage * rectangles clipped to &drm_plane_state.src. + * + * Note that there are two types of damage handling: frame damage and buffer + * damage. The type of damage handling implemented depends on a driver's upload + * target. Drivers implementing a per-plane or per-CRTC upload target need to + * handle frame damage while drivers implementing a per-buffer upload target + * need to handle buffer damage. + * + * The existing damage helpers only support the frame damage type, there is no + * buffer age support or similar damage accumulation algorithm implemented yet. + * + * Only drivers handling frame damage can use the mentiored damage helpers to + * iterate over the damaged regions. Drivers that handle buffer damage, need to + * set &struct drm_plane_state.ignore_damage_clips as an indication to + * drm_atomic_helper_damage_iter_init() that the damage clips should be ignored. + * In that case, the returned damage rectangle is the &drm_plane_state.src since + * a full plane update should happen. + * + * For more information about the two type of damage, see: + * https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_swap_buffers_with_damage.txt + * https://emersion.fr/blog/2019/intro-to-damage-tracking/
One thought you might want to consider.These URLs are helpful. The only issue I have is that frame damage and buffer damage are user-space concepts. The kernel bug is that damage handling expects the backing storage/upload buffer not to change for a given plane. If the upload buffer changes between page flips, the new upload buffer has to be updated as a whole. Hence no damage handling then.
And then maybe say that the effects of frame damage and buffer damage in userspace illustrate this problem and give the URLs.
Best regards Thomas
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-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
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