[PATCH] drm/amdgpu/display: flush the HDP when setting up DMCUB firmware

[Alex Deucher]

When data is written to VRAM via the PCI BAR, the data goes
through a block called HDP which has a write queue and a
read cache.  When the driver writes to VRAM, it needs to flush
the HDP write queue to make sure all the data written has
actually hit VRAM.

When we write the DMCUB firmware to vram, we never flushed the
HDP.  In theory this could cause DMCUB errors if we try and
start the DMCUB firmware without making sure the data has hit
memory.

This doesn't fix any known issues, but is the right thing to do.

Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index a6c3e1d74124..5c1fd3a91cd5 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1133,6 +1133,10 @@ static int dm_dmub_hw_init(struct amdgpu_device *adev)
 		break;
 	}
 
+	/* flush HDP */
+	mb();
+	amdgpu_device_flush_hdp(adev, NULL);
+
 	status = dmub_srv_hw_init(dmub_srv, &hw_params);
 	if (status != DMUB_STATUS_OK) {
 		DRM_ERROR("Error initializing DMUB HW: %d\n", status);
-- 
2.35.1