Commit 440a11b9 authored by Mario Kleiner's avatar Mario Kleiner Committed by Greg Kroah-Hartman

drm: Fix timestamp docs for variable refresh properties.

commit 0cbd0adc upstream.

As discussed with Nicholas and Daniel Vetter (patchwork
link to discussion below), the VRR timestamping behaviour
produced utterly useless and bogus vblank/pageflip
timestamps. We have found a way to fix this and provide
sane behaviour.

As of Linux 5.2, the amdgpu driver will be able to
provide exactly the same vblank / pageflip timestamp
semantic in variable refresh rate mode as in standard
fixed refresh rate mode. This is achieved by deferring
core vblank handling (drm_crtc_handle_vblank()) until
the end of front porch, and also defer the sending of
pageflip completion events until end of front porch,
when we can safely compute correct pageflip/vblank
timestamps.

The same approach will be possible for other VRR
capable kms drivers, so we can actually have sane
and useful timestamps in VRR mode.

This patch removes the section of the docs that
describes the broken timestamp behaviour present
in Linux 5.0/5.1.

Fixes: ab7a664f ("drm: Document variable refresh properties")
Link: https://patchwork.freedesktop.org/patch/285333/Acked-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: default avatarNicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: default avatarMario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190418060157.18968-1-mario.kleiner.de@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b7a8b913
......@@ -1385,12 +1385,6 @@ EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
*
* The driver may place further restrictions within these minimum
* and maximum bounds.
*
* The semantics for the vertical blank timestamp differ when
* variable refresh rate is active. The vertical blank timestamp
* is defined to be an estimate using the current mode's fixed
* refresh rate timings. The semantics for the page-flip event
* timestamp remain the same.
*/
/**
......
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