[PATCH] drm/radeon: fix rare segfault after gpu lockup on r7xx

[j.gli...@gmail.com]

From: Jerome Glisse <jgli...@redhat.com>

If GPU reset fails the gart table ptr might be NULL avoid a
kernel segfault in this rare event.

Signed-off-by: Jerome Glisse <jglisse at redhat.com>
---
 drivers/gpu/drm/radeon/r600.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
index cda280d..0e3a68a 100644
--- a/drivers/gpu/drm/radeon/r600.c
+++ b/drivers/gpu/drm/radeon/r600.c
@@ -843,7 +843,9 @@ void r600_pcie_gart_tlb_flush(struct radeon_device *rdev)
                 * method for them.
                 */
                WREG32(HDP_DEBUG1, 0);
-               tmp = readl((void __iomem *)ptr);
+               if (ptr) {
+                       tmp = readl((void __iomem *)ptr);
+               }
        } else
                WREG32(R_005480_HDP_MEM_COHERENCY_FLUSH_CNTL, 0x1);

-- 
1.7.11.7