drm/radeon/kms: enable writeback (v2)

When writeback is enabled, the GPU shadows writes to certain
registers into a buffer in memory.  The driver can then read
the values from the shadow rather than reading back from the
register across the bus.  Writeback can be disabled by setting
the no_wb module param to 1.

On r6xx/r7xx/evergreen, the following registers are shadowed:
- CP scratch registers
- CP read pointer
- IH write pointer
On r1xx-rr5xx, the following registers are shadowed:
- CP scratch registers
- CP read pointer

v2:
- Combine wb patches for r6xx-evergreen and r1xx-r5xx
- Writeback is disabled on AGP boards since it tends to be
unreliable on AGP using the gart.
- Check radeon_wb_init return values properly.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_ring.c b/drivers/gpu/drm/radeon/radeon_ring.c
index 261e98a276d..6ea798ce821 100644
--- a/drivers/gpu/drm/radeon/radeon_ring.c
+++ b/drivers/gpu/drm/radeon/radeon_ring.c
@@ -247,10 +247,14 @@ void radeon_ib_pool_fini(struct radeon_device *rdev)
  */
 void radeon_ring_free_size(struct radeon_device *rdev)
 {
-	if (rdev->family >= CHIP_R600)
-		rdev->cp.rptr = RREG32(R600_CP_RB_RPTR);
-	else
-		rdev->cp.rptr = RREG32(RADEON_CP_RB_RPTR);
+	if (rdev->wb.enabled)
+		rdev->cp.rptr = rdev->wb.wb[RADEON_WB_CP_RPTR_OFFSET/4];
+	else {
+		if (rdev->family >= CHIP_R600)
+			rdev->cp.rptr = RREG32(R600_CP_RB_RPTR);
+		else
+			rdev->cp.rptr = RREG32(RADEON_CP_RB_RPTR);
+	}
 	/* This works because ring_size is a power of 2 */
 	rdev->cp.ring_free_dw = (rdev->cp.rptr + (rdev->cp.ring_size / 4));
 	rdev->cp.ring_free_dw -= rdev->cp.wptr;