Revision 69d9f4278d0f9d24607645f10e5ac5c59c77a4ac authored by Alexander Monakov on 04 August 2020, 20:13:13 UTC, committed by Alex Deucher on 26 August 2020, 19:11:40 UTC
Documentation for sysfs backlight level interface requires that
values in both 'brightness' and 'actual_brightness' files are
interpreted to be in range from 0 to the value given in the
'max_brightness' file.

With amdgpu, max_brightness gives 255, and values written by the user
into 'brightness' are internally rescaled to a wider range. However,
reading from 'actual_brightness' gives the raw register value without
inverse rescaling. This causes issues for various userspace tools such
as PowerTop and systemd that expect the value to be in the correct
range.

Introduce a helper to retrieve internal backlight range. Use it to
reimplement 'convert_brightness' as 'convert_brightness_from_user' and
introduce 'convert_brightness_to_user'.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=203905
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1242
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
1 parent ed9ab22
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