[PATCH] drm/amdgpu: GFX10: GRBM requires 1-cycle delay (v2)

[Tuikov, Luben]

The GRBM interface is now capable of bursting
1-cycle op per register, a WRITE followed by
another WRITE, or a WRITE followed by a READ--much
faster than previous muti-cycle per
completed-transaction interface. This causes a
problem, whereby status registers requiring a
read/write by hardware, have a 1-cycle delay, due
to the register update having to go through GRBM
interface.

This patch adds this delay.

A one cycle read op is added after updating the
invalidate request and before reading the
invalidate-ACK status.

See also commit
534991731cb5fa94b5519957646cf849ca10d17d.

v2: Remove GFX9 and apply only to SDMA ring.

Signed-off-by: Luben Tuikov <luben.tuikov at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c | 7 +++++++
 drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c | 2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
index 6e1b25bd1fe7..dedd7e1ab2fb 100644
--- a/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
@@ -346,6 +346,13 @@ static uint64_t gmc_v10_0_emit_flush_gpu_tlb(struct amdgpu_ring *ring,
 
 	amdgpu_ring_emit_wreg(ring, hub->vm_inv_eng0_req + eng, req);
 
+	/* Insert a dummy read to delay one cycle after the write REQ,
+	 * and before the ACK inquiry.
+	 */
+	if (ring->funcs->type == AMDGPU_RING_TYPE_SDMA)
+		amdgpu_ring_emit_reg_wait(ring,
+					  hub->vm_inv_eng0_req + eng, 0, 0);
+
 	/* wait for the invalidate to complete */
 	amdgpu_ring_emit_reg_wait(ring, hub->vm_inv_eng0_ack + eng,
 				  1 << vmid, 1 << vmid);
diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c b/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
index b8fdb192f6d6..0c41b4fdc58b 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v5_0.c
@@ -1588,7 +1588,7 @@ static const struct amdgpu_ring_funcs sdma_v5_0_ring_funcs = {
 		6 + /* sdma_v5_0_ring_emit_pipeline_sync */
 		/* sdma_v5_0_ring_emit_vm_flush */
 		SOC15_FLUSH_GPU_TLB_NUM_WREG * 3 +
-		SOC15_FLUSH_GPU_TLB_NUM_REG_WAIT * 6 +
+		SOC15_FLUSH_GPU_TLB_NUM_REG_WAIT * 6 * 2 +
 		10 + 10 + 10, /* sdma_v5_0_ring_emit_fence x3 for user fence, vm fence */
 	.emit_ib_size = 7 + 6, /* sdma_v5_0_ring_emit_ib */
 	.emit_ib = sdma_v5_0_ring_emit_ib,
-- 
2.23.0.385.gbc12974a89