[PATCH v8 09/14] drm/amdgpu: Check bios_scratch_reg_offset in backlight level helper

[Mario Limonciello <mario.limonciello@amd.com>]

From: "Mario Limonciello (AMD)" <superm1@kernel.org>

Ensure adev->bios_scratch_reg_offset is non-zero before accessing
scratch registers in amdgpu_atombios_scratch_regs_set_backlight_level()
to avoid dereferencing unmapped MMIO offsets.

Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c
index 27c0dc8f6137a..2d8c2ba04e670 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c
@@ -1622,7 +1622,12 @@ void amdgpu_atombios_scratch_regs_engine_hung(struct amdgpu_device *adev,
 void amdgpu_atombios_scratch_regs_set_backlight_level(struct amdgpu_device *adev,
 						      u32 backlight_level)
 {
-	u32 tmp = RREG32(adev->bios_scratch_reg_offset + 2);
+	u32 tmp;
+
+	if (!adev->bios_scratch_reg_offset)
+		return;
+
+	tmp = RREG32(adev->bios_scratch_reg_offset + 2);
 
 	tmp &= ~ATOM_S2_CURRENT_BL_LEVEL_MASK;
 	tmp |= (backlight_level << ATOM_S2_CURRENT_BL_LEVEL_SHIFT) &
-- 
2.43.0