drm/amd/display: Fix LFC multiplier changing erratically

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[Why]
1. There is a calculation that is using frame_time_in_us instead of
last_render_time_in_us to calculate whether choosing an LFC multiplier
would cause the inserted frame duration to be outside of range.

2. We do not handle unsigned integer subtraction correctly and it underflows
to a really large value, which causes some logic errors.

[How]
1. Fix logic to calculate 'within range' using last_render_time_in_us
2. Split out delta_from_mid_point_delta_in_us calculation to ensure
we don't underflow and wrap around

Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

...

This commit is contained in:

Anthony Koo 2020-07-29 17:33:27 -04:00 • committed by Alex Deucher

parent c0c96fc9c2

commit 575da8db31

1 changed files with 29 additions and 7 deletions

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drivers/gpu/drm/amd/display/modules/freesync/freesync.c

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