[PATCH v2] drm/msm: Be more robust when HFI response times out

[Connor Abbott]

If the GMU takes too long to respond to an HFI message, we may return
early. If the GMU does eventually respond, and then we send a second
message, we will see the response for the first, throw another error,
and keep going. But we don't currently wait for the interrupt from the
GMU again, so if the second response isn't there immediately we may
prematurely return. This can cause a continuous cycle of missed HFI
messages, and for reasons I don't quite understand the GMU does not shut
down properly when this happens.

Fix this by waiting for the GMU interrupt when we see an empty queue. If
the GMU never responds then the queue really is empty and we quit. We
can't wait for the interrupt when we see a wrong response seqnum because
the GMU might have already queued both responses by the time we clear
the interrupt the first time so we do need to check the queue before
waiting on the interrupt again.

Signed-off-by: Connor Abbott <cwabbott0 at gmail.com>
---
Changes in v2:
- Add back error print about the queue being empty if we timeout while
  waiting for a message when the queue is empty.
- Link to v1: https://lore.kernel.org/r/20250422-msm-hfi-resp-fix-v1-1-b0ba02b93b91@gmail.com
---
 drivers/gpu/drm/msm/adreno/a6xx_hfi.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_hfi.c b/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
index 0989aee3dd2cf9bc3405c3b25a595c22e6f06387..1bc40d667281a22a34e4f510b2a1333f9c5675c6 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
@@ -100,12 +100,10 @@ static int a6xx_hfi_queue_write(struct a6xx_gmu *gmu,
 	return 0;
 }
 
-static int a6xx_hfi_wait_for_ack(struct a6xx_gmu *gmu, u32 id, u32 seqnum,
-		u32 *payload, u32 payload_size)
+static int a6xx_hfi_wait_for_msg_interrupt(struct a6xx_gmu *gmu, u32 id, u32 seqnum)
 {
-	struct a6xx_hfi_queue *queue = &gmu->queues[HFI_RESPONSE_QUEUE];
-	u32 val;
 	int ret;
+	u32 val;
 
 	/* Wait for a response */
 	ret = gmu_poll_timeout(gmu, REG_A6XX_GMU_GMU2HOST_INTR_INFO, val,
@@ -122,6 +120,19 @@ static int a6xx_hfi_wait_for_ack(struct a6xx_gmu *gmu, u32 id, u32 seqnum,
 	gmu_write(gmu, REG_A6XX_GMU_GMU2HOST_INTR_CLR,
 		A6XX_GMU_GMU2HOST_INTR_INFO_MSGQ);
 
+	return 0;
+}
+
+static int a6xx_hfi_wait_for_ack(struct a6xx_gmu *gmu, u32 id, u32 seqnum,
+		u32 *payload, u32 payload_size)
+{
+	struct a6xx_hfi_queue *queue = &gmu->queues[HFI_RESPONSE_QUEUE];
+	int ret;
+
+	ret = a6xx_hfi_wait_for_msg_interrupt(gmu, id, seqnum);
+	if (ret)
+		return ret;
+
 	for (;;) {
 		struct a6xx_hfi_msg_response resp;
 
@@ -129,12 +140,18 @@ static int a6xx_hfi_wait_for_ack(struct a6xx_gmu *gmu, u32 id, u32 seqnum,
 		ret = a6xx_hfi_queue_read(gmu, queue, (u32 *) &resp,
 			sizeof(resp) >> 2);
 
-		/* If the queue is empty our response never made it */
+		/* If the queue is empty, there may have been previous missed
+		 * responses that preceded the response to our packet. Wait
+		 * further before we give up.
+		 */
 		if (!ret) {
-			DRM_DEV_ERROR(gmu->dev,
-				"The HFI response queue is unexpectedly empty\n");
-
-			return -ENOENT;
+			ret = a6xx_hfi_wait_for_msg_interrupt(gmu, id, seqnum);
+			if (ret) {
+				DRM_DEV_ERROR(gmu->dev,
+					"The HFI response queue is unexpectedly empty\n");
+				return ret;
+			}
+			continue;
 		}
 
 		if (HFI_HEADER_ID(resp.header) == HFI_F2H_MSG_ERROR) {

---
base-commit: 866e43b945bf98f8e807dfa45eca92f931f3a032
change-id: 20250422-msm-hfi-resp-fix-58ab3a19554f

Best regards,
-- 
Connor Abbott <cwabbott0 at gmail.com>