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

[j.glisse at gmail.com]

From: Jerome Glisse <jglisse at 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