drm/radeon: fix fence value access

It is possible that radeon_fence_process is called
after writeback is disabled for suspend, leading
to an invalid read of register 0x0.

This fixes a problem for me where the fence value
is temporary incremented by 0x100000000 on
suspend/resume.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_fence.c b/drivers/gpu/drm/radeon/radeon_fence.c
index be4e4f390e89..a194a142f898 100644
--- a/drivers/gpu/drm/radeon/radeon_fence.c
+++ b/drivers/gpu/drm/radeon/radeon_fence.c
@@ -42,21 +42,23 @@
 
 static void radeon_fence_write(struct radeon_device *rdev, u32 seq, int ring)
 {
-        if (rdev->wb.enabled) {
-                *rdev->fence_drv[ring].cpu_addr = cpu_to_le32(seq);
+        struct radeon_fence_driver *drv = &rdev->fence_drv[ring];
+        if (likely(rdev->wb.enabled || !drv->scratch_reg)) {
+                *drv->cpu_addr = cpu_to_le32(seq);
         } else {
-                WREG32(rdev->fence_drv[ring].scratch_reg, seq);
+                WREG32(drv->scratch_reg, seq);
         }
 }
 
 static u32 radeon_fence_read(struct radeon_device *rdev, int ring)
 {
+        struct radeon_fence_driver *drv = &rdev->fence_drv[ring];
         u32 seq = 0;
 
-        if (rdev->wb.enabled) {
-                seq = le32_to_cpu(*rdev->fence_drv[ring].cpu_addr);
+        if (likely(rdev->wb.enabled || !drv->scratch_reg)) {
+                seq = le32_to_cpu(*drv->cpu_addr);
         } else {
-                seq = RREG32(rdev->fence_drv[ring].scratch_reg);
+                seq = RREG32(drv->scratch_reg);
         }
         return seq;
 }