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On clients that utilize AMD_PRIVATE_COLOR properties for HDR support, brightness sliders can include a hardware controlled portion and a gamma-based portion. This is the case on the Steam Deck OLED when using gamescope with Steam as a client. When a user sets a brightness level while HDR is active, the gamma-based portion and/or hardware portion are adjusted to achieve the desired brightness. However, when a modeset takes place while the gamma-based portion is in-use, restoring the hardware brightness level overrides the user's overall brightness level and results in a mismatch between what the slider reports and the display's current brightness. To avoid overriding gamma-based brightness, only restore HW backlight level after boot or resume. This ensures that the backlight level is set correctly after the DC layer resets it while avoiding interference with subsequent modesets. Fixes:7875afafba("drm/amd/display: Fix brightness level not retained over reboot") Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4551 Signed-off-by: Matthew Schwartz <matthew.schwartz@linux.dev> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com> (cherry picked from commita490c8d77d) Cc: stable@vger.kernel.org