Re: [PATCH v2] drm/msm/dpu: make "vblank timeout" more useful

From: Abhinav Kumar
Date: Wed Feb 14 2024 - 15:36:18 EST

On 2/14/2024 11:20 AM, Dmitry Baryshkov wrote:
On Wed, 14 Feb 2024 at 20:02, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:

On 2/8/2024 6:50 AM, Dmitry Baryshkov wrote:
We have several reports of vblank timeout messages. However after some
debugging it was found that there might be different causes to that.
To allow us to identify the DPU block that gets stuck, include the
actual CTL_FLUSH value into the timeout message and trigger the devcore
snapshot capture.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Changes in v2:
- Added a call to msm_disp_snapshot_state() to trigger devcore dump
- Link to v1:
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
index d0f56c5c4cce..a8d6165b3c0a 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
@@ -489,7 +489,8 @@ static int dpu_encoder_phys_vid_wait_for_commit_done(
(hw_ctl->ops.get_flush_register(hw_ctl) == 0),
if (ret <= 0) {
- DPU_ERROR("vblank timeout\n");
+ DPU_ERROR("vblank timeout: %x\n", hw_ctl->ops.get_flush_register(hw_ctl));
+ msm_disp_snapshot_state(phys_enc->parent->dev);

There is no rate limiting in this piece of code unfortunately. So this
will flood the number of snapshots.

Well... Yes and no. The devcoredump will destroy other snapshots if
there is a pending one. So only the console will be flooded and only
in case when MSM_DISP_SNAPSHOT_DUMP_IN_CONSOLE is enabled.

Yes, true but at the same time this makes it hard to capture a good dump as potentially every vblank you could timeout so this destroy/create cycle wont end.

Short-term solution is you can go with a vblank_timeout_cnt and reset it
in the enable() like other similar error counters.

long-term solution is we need to centralize these error locations to one
single dpu_encoder_error_handler() with a single counter and the error
handler will print out the error code along with the snapshot instead of
the snapshot being called from all over the place.

return -ETIMEDOUT;

base-commit: 39676dfe52331dba909c617f213fdb21015c8d10
change-id: 20240106-fd-dpu-debug-timeout-e917f0bc8063

Best regards,