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

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On 2/19/2024 3:52 AM, Dmitry Baryshkov wrote:
On Wed, 14 Feb 2024 at 22:36, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:

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.

Excuse me, maybe I miss something. On the first timeout the snapshot
is created. It is held by the kernel until it is fully read out from
the userspace. Other snapshots will not interfere with this snapshot.

For every new snapshot a new devcoredump device will be created which should remain till it has been read. But now this will be created every blank. IMO, this is really too much data for no reason.

Subsequent vblank timeouts are not going to give any new information compared to the existing snapshot of the first vblank timeout thats why we should just create the snapshot when the first error happens and stop.

For other frame done timeouts, infact subsequent timeouts without any sort of recovery in between are quite misleading because hardware was already not able to fetch the previous frame so it will most likely not fetch the next one either till it has recovered. Typically thats why these vblank timeouts happen in a flurry as the hardware never really recovered from the first timeout.

Or are you worried that snapshotting takes time, so taking a snapshot
will also interfere with the vblank timings for the next vblank?

Yes this is another point.

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