From 9b33df36b45136d301241920d13a0a3ecc77b8f9 Mon Sep 17 00:00:00 2001 From: Pekka Paalanen Date: Mon, 14 Apr 2025 08:56:56 +0000 Subject: [PATCH 3394/5403] drm/doc: document front-buffer rendering Explain how to perform front-buffer rendering. v2: apply Pekka's rewrite Signed-off-by: Pekka Paalanen Signed-off-by: Simon Ser Reviewed-by: Simon Ser Link: https://lore.kernel.org/r/20250414085652.43904-1-contact@emersion.fr --- drivers/gpu/drm/drm_blend.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c index 6e74de833466..6852d73c931c 100644 --- a/drivers/gpu/drm/drm_blend.c +++ b/drivers/gpu/drm/drm_blend.c @@ -75,6 +75,12 @@ * the currently visible vertical area of the &drm_crtc. * FB_ID: * Mode object ID of the &drm_framebuffer this plane should scan out. + * + * When a KMS client is performing front-buffer rendering, it should set + * FB_ID to the same front-buffer FB on each atomic commit. This implies + * to the driver that it needs to re-read the same FB again. Otherwise + * drivers which do not employ continuously repeated scanout cycles might + * not update the screen. * CRTC_ID: * Mode object ID of the &drm_crtc this plane should be connected to. * -- 2.54.0