diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
index e1e59e1b318d4a2f6c7f2b0578d8aa1d6eaee936..28e39bc6768b652385a675e17f3300a44ea46150 100644
--- a/drivers/gpu/drm/radeon/r600.c
+++ b/drivers/gpu/drm/radeon/r600.c
@@ -884,7 +884,17 @@ void r600_pcie_gart_tlb_flush(struct radeon_device *rdev)
 	u32 tmp;
 
 	/* flush hdp cache so updates hit vram */
-	WREG32(R_005480_HDP_MEM_COHERENCY_FLUSH_CNTL, 0x1);
+	if ((rdev->family >= CHIP_RV770) && (rdev->family <= CHIP_RV740)) {
+		void __iomem *ptr = (void *)rdev->gart.table.vram.ptr;
+		u32 tmp;
+
+		/* r7xx hw bug.  write to HDP_DEBUG1 followed by fb read
+		 * rather than write to HDP_REG_COHERENCY_FLUSH_CNTL
+		 */
+		WREG32(HDP_DEBUG1, 0);
+		tmp = readl((void __iomem *)ptr);
+	} else
+		WREG32(R_005480_HDP_MEM_COHERENCY_FLUSH_CNTL, 0x1);
 
 	WREG32(VM_CONTEXT0_INVALIDATION_LOW_ADDR, rdev->mc.gtt_start >> 12);
 	WREG32(VM_CONTEXT0_INVALIDATION_HIGH_ADDR, (rdev->mc.gtt_end - 1) >> 12);
@@ -3527,5 +3537,15 @@ int r600_debugfs_mc_info_init(struct radeon_device *rdev)
  */
 void r600_ioctl_wait_idle(struct radeon_device *rdev, struct radeon_bo *bo)
 {
-	WREG32(R_005480_HDP_MEM_COHERENCY_FLUSH_CNTL, 0x1);
+	/* r7xx hw bug.  write to HDP_DEBUG1 followed by fb read
+	 * rather than write to HDP_REG_COHERENCY_FLUSH_CNTL
+	 */
+	if ((rdev->family >= CHIP_RV770) && (rdev->family <= CHIP_RV740)) {
+		void __iomem *ptr = (void *)rdev->gart.table.vram.ptr;
+		u32 tmp;
+
+		WREG32(HDP_DEBUG1, 0);
+		tmp = readl((void __iomem *)ptr);
+	} else
+		WREG32(R_005480_HDP_MEM_COHERENCY_FLUSH_CNTL, 0x1);
 }
diff --git a/drivers/gpu/drm/radeon/r600d.h b/drivers/gpu/drm/radeon/r600d.h
index b7318ac4f84ab323f96e5f26d88eb280edfccc8a..858a1920c0d76bb2c916c847c8b2751058d7e9d5 100644
--- a/drivers/gpu/drm/radeon/r600d.h
+++ b/drivers/gpu/drm/radeon/r600d.h
@@ -250,6 +250,7 @@
 #define	HDP_NONSURFACE_SIZE				0x2C0C
 #define HDP_REG_COHERENCY_FLUSH_CNTL			0x54A0
 #define	HDP_TILING_CONFIG				0x2F3C
+#define HDP_DEBUG1                                      0x2F34
 
 #define MC_VM_AGP_TOP					0x2184
 #define MC_VM_AGP_BOT					0x2188
diff --git a/drivers/gpu/drm/radeon/rv770.c b/drivers/gpu/drm/radeon/rv770.c
index 236fe66819222e0b7234cc6e9f8a2b9940dd0d59..f1c796810117fdb9dfb0b66aa5a89eee5e1da1e9 100644
--- a/drivers/gpu/drm/radeon/rv770.c
+++ b/drivers/gpu/drm/radeon/rv770.c
@@ -204,7 +204,10 @@ static void rv770_mc_program(struct radeon_device *rdev)
 		WREG32((0x2c20 + j), 0x00000000);
 		WREG32((0x2c24 + j), 0x00000000);
 	}
-	WREG32(HDP_REG_COHERENCY_FLUSH_CNTL, 0);
+	/* r7xx hw bug.  Read from HDP_DEBUG1 rather
+	 * than writing to HDP_REG_COHERENCY_FLUSH_CNTL
+	 */
+	tmp = RREG32(HDP_DEBUG1);
 
 	rv515_mc_stop(rdev, &save);
 	if (r600_mc_wait_for_idle(rdev)) {
diff --git a/drivers/gpu/drm/radeon/rv770d.h b/drivers/gpu/drm/radeon/rv770d.h
index fd733f268e3d605b1deaad2da851c954ea183fbb..b7a5a20e81dc444b1a85a5944e5e7fb87f07f2ce 100644
--- a/drivers/gpu/drm/radeon/rv770d.h
+++ b/drivers/gpu/drm/radeon/rv770d.h
@@ -133,6 +133,7 @@
 #define	HDP_NONSURFACE_SIZE				0x2C0C
 #define HDP_REG_COHERENCY_FLUSH_CNTL			0x54A0
 #define	HDP_TILING_CONFIG				0x2F3C
+#define HDP_DEBUG1                                      0x2F34
 
 #define MC_SHARED_CHMAP						0x2004
 #define		NOOFCHAN_SHIFT					12