drm/radeon/kms: Don't RMW CP_RB_CNTL

Immediate readback seems faulty on some chips.  I
suspect it takes a while to get through the fifo
to the actual register backbone.  There's no need
to read it back, so, just write the driver's copy
of the register's value directly.

Should fix bug 24535 and possibly 24218
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/r100.c

@@ -578,19 +578,19 @@ int r100_cp_init(struct radeon_device *rdev, unsigned ring_size)
 	indirect1_start = 16;
 	/* cp setup */
 	WREG32(0x718, pre_write_timer | (pre_write_limit << 28));
-	WREG32(RADEON_CP_RB_CNTL,
-#ifdef __BIG_ENDIAN
-	       RADEON_BUF_SWAP_32BIT |
-#endif
-	       REG_SET(RADEON_RB_BUFSZ, rb_bufsz) |
+	tmp = (REG_SET(RADEON_RB_BUFSZ, rb_bufsz) |
 	       REG_SET(RADEON_RB_BLKSZ, rb_blksz) |
 	       REG_SET(RADEON_MAX_FETCH, max_fetch) |
 	       RADEON_RB_NO_UPDATE);
+#ifdef __BIG_ENDIAN
+	tmp |= RADEON_BUF_SWAP_32BIT;
+#endif
+	WREG32(RADEON_CP_RB_CNTL, tmp);
+
 	/* Set ring address */
 	DRM_INFO("radeon: ring at 0x%016lX\n", (unsigned long)rdev->cp.gpu_addr);
 	WREG32(RADEON_CP_RB_BASE, rdev->cp.gpu_addr);
 	/* Force read & write ptr to 0 */
-	tmp = RREG32(RADEON_CP_RB_CNTL);
 	WREG32(RADEON_CP_RB_CNTL, tmp | RADEON_RB_RPTR_WR_ENA);
 	WREG32(RADEON_CP_RB_RPTR_WR, 0);
 	WREG32(RADEON_CP_RB_WPTR, 0);

drivers/gpu/drm/radeon/r600.c

@@ -1272,19 +1272,17 @@ int r600_cp_resume(struct radeon_device *rdev)
 
 	/* Set ring buffer size */
 	rb_bufsz = drm_order(rdev->cp.ring_size / 8);
+	tmp = RB_NO_UPDATE | (drm_order(RADEON_GPU_PAGE_SIZE/8) << 8) | rb_bufsz;
 #ifdef __BIG_ENDIAN
-	WREG32(CP_RB_CNTL, BUF_SWAP_32BIT | RB_NO_UPDATE |
-		(drm_order(RADEON_GPU_PAGE_SIZE/8) << 8) | rb_bufsz);
-#else
-	WREG32(CP_RB_CNTL, RB_NO_UPDATE | (drm_order(RADEON_GPU_PAGE_SIZE/8) << 8) | rb_bufsz);
+	tmp |= BUF_SWAP_32BIT;
 #endif
+	WREG32(CP_RB_CNTL, tmp);
 	WREG32(CP_SEM_WAIT_TIMER, 0x4);
 
 	/* Set the write pointer delay */
 	WREG32(CP_RB_WPTR_DELAY, 0);
 
 	/* Initialize the ring buffer's read and write pointers */
-	tmp = RREG32(CP_RB_CNTL);
 	WREG32(CP_RB_CNTL, tmp | RB_RPTR_WR_ENA);
 	WREG32(CP_RB_RPTR_WR, 0);
 	WREG32(CP_RB_WPTR, 0);