[PATCH] drm/amdgpu/sdma5.2: Update wptr registers as well as doorbell

[Alex Deucher]

We seem to have a case where SDMA will sometimes miss a doorbell
if GFX is entering the powergating state when the doorbell comes in.
To workaround this, we can update the wptr via MMIO, however,
this is only safe because we disallow gfxoff in begin_ring() for
SDMA 5.2 and then allow it again in end_ring().

Enable this workaround while we are root causing the issue with
the HW team.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/3440
Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c b/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
index 7e475d9b554e..3c37e3cd3cbf 100644
--- a/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
+++ b/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
@@ -225,6 +225,14 @@ static void sdma_v5_2_ring_set_wptr(struct amdgpu_ring *ring)
 		DRM_DEBUG("calling WDOORBELL64(0x%08x, 0x%016llx)\n",
 				ring->doorbell_index, ring->wptr << 2);
 		WDOORBELL64(ring->doorbell_index, ring->wptr << 2);
+		/* SDMA seems to miss doorbells sometimes when powergating kicks in.
+		 * Updating the wptr directly will wake it. This is only safe because
+		 * we disallow gfxoff in begin_use() and then allow it again in end_use().
+		 */
+		WREG32(sdma_v5_2_get_reg_offset(adev, ring->me, mmSDMA0_GFX_RB_WPTR),
+		       lower_32_bits(ring->wptr << 2));
+		WREG32(sdma_v5_2_get_reg_offset(adev, ring->me, mmSDMA0_GFX_RB_WPTR_HI),
+		       upper_32_bits(ring->wptr << 2));
 	} else {
 		DRM_DEBUG("Not using doorbell -- "
 				"mmSDMA%i_GFX_RB_WPTR == 0x%08x "
@@ -1707,6 +1715,10 @@ static void sdma_v5_2_ring_begin_use(struct amdgpu_ring *ring)
 	 * but it shouldn't hurt for other parts since
 	 * this GFXOFF will be disallowed anyway when SDMA is
 	 * active, this just makes it explicit.
+	 * sdma_v5_2_ring_set_wptr() takes advantage of this
+	 * to update the wptr because sometimes SDMA seems to miss
+	 * doorbells when entering PG.  If you remove this, update
+	 * sdma_v5_2_ring_set_wptr() as well!
 	 */
 	amdgpu_gfx_off_ctrl(adev, false);
 }
-- 
2.45.2