drm/amd/display: update bios scratch when setting backlight

Update the bios scratch register when updating the backlight
level.  Some platforms apparently read this scratch register
and do additional operations in their hotkey handlers.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1518
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c

@@ -1569,6 +1569,18 @@ void amdgpu_atombios_scratch_regs_engine_hung(struct amdgpu_device *adev,
 	WREG32(adev->bios_scratch_reg_offset + 3, tmp);
 }
 
+void amdgpu_atombios_scratch_regs_set_backlight_level(struct amdgpu_device *adev,
+						      u32 backlight_level)
+{
+	u32 tmp = RREG32(adev->bios_scratch_reg_offset + 2);
+
+	tmp &= ~ATOM_S2_CURRENT_BL_LEVEL_MASK;
+	tmp |= (backlight_level << ATOM_S2_CURRENT_BL_LEVEL_SHIFT) &
+		ATOM_S2_CURRENT_BL_LEVEL_MASK;
+
+	WREG32(adev->bios_scratch_reg_offset + 2, tmp);
+}
+
 bool amdgpu_atombios_scratch_need_asic_init(struct amdgpu_device *adev)
 {
 	u32 tmp = RREG32(adev->bios_scratch_reg_offset + 7);

drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.h

@@ -185,6 +185,8 @@ bool amdgpu_atombios_has_gpu_virtualization_table(struct amdgpu_device *adev);
 void amdgpu_atombios_scratch_regs_lock(struct amdgpu_device *adev, bool lock);
 void amdgpu_atombios_scratch_regs_engine_hung(struct amdgpu_device *adev,
 					      bool hung);
+void amdgpu_atombios_scratch_regs_set_backlight_level(struct amdgpu_device *adev,
+						      u32 backlight_level);
 bool amdgpu_atombios_scratch_need_asic_init(struct amdgpu_device *adev);
 
 void amdgpu_atombios_copy_swap(u8 *dst, u8 *src, u8 num_bytes, bool to_le);

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -51,6 +51,7 @@
 #include <drm/drm_hdcp.h>
 #endif
 #include "amdgpu_pm.h"
+#include "amdgpu_atombios.h"
 
 #include "amd_shared.h"
 #include "amdgpu_dm_irq.h"
@@ -3925,6 +3926,9 @@ static int amdgpu_dm_backlight_set_level(struct amdgpu_display_manager *dm,
 	caps = dm->backlight_caps[bl_idx];
 
 	dm->brightness[bl_idx] = user_brightness;
+	/* update scratch register */
+	if (bl_idx == 0)
+		amdgpu_atombios_scratch_regs_set_backlight_level(dm->adev, dm->brightness[bl_idx]);
 	brightness = convert_brightness_from_user(&caps, dm->brightness[bl_idx]);
 	link = (struct dc_link *)dm->backlight_link[bl_idx];