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, 5 insertions, 1 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_fence.c b/drivers/gpu/drm/radeon/radeon_fence.c
index b1f9a81..698a7ed 100644
--- a/drivers/gpu/drm/radeon/radeon_fence.c
+++ b/drivers/gpu/drm/radeon/radeon_fence.c
@@ -72,7 +72,11 @@ static bool radeon_fence_poll_locked(struct radeon_device *rdev)
 	bool wake = false;
 	unsigned long cjiffies;
 
-	seq = RREG32(rdev->fence_drv.scratch_reg);
+	if (rdev->wb.enabled) {
+		u32 scratch_index = RADEON_WB_SCRATCH_OFFSET + rdev->fence_drv.scratch_reg - rdev->scratch.reg_base;
+		seq = rdev->wb.wb[scratch_index/4];
+	} else
+		seq = RREG32(rdev->fence_drv.scratch_reg);
 	if (seq != rdev->fence_drv.last_seq) {
 		rdev->fence_drv.last_seq = seq;
 		rdev->fence_drv.last_jiffies = jiffies;