linux-kernel - Re: [PATCH v2] drm/panfrost: Sync IRQ by job's timeout handler

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Message-ID: <20230724085723.5e574bff@collabora.com>
Date:   Mon, 24 Jul 2023 08:57:23 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v2] drm/panfrost: Sync IRQ by job's timeout handler

On Sun, 23 Jul 2023 03:01:42 +0300
Dmitry Osipenko <dmitry.osipenko@...labora.com> wrote:

> Panfrost IRQ handler may stuck for a long time, for example this happens
> when there is a bad HDMI connection and HDMI handler takes a long time to
> finish processing, holding Panfrost. Make Panfrost's job timeout handler
> to sync IRQ before checking fence signal status in order to prevent
> spurious job timeouts due to a slow IRQ processing.
> 
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
> 
> Changelog:
> 
> v2: - Moved synchronize_irq() after first signal-check to avoid unnecessary
>       blocking on syncing.
> 
>     - Added warn message about high interrupt latency.
> 
>  drivers/gpu/drm/panfrost/panfrost_job.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index dbc597ab46fb..a7663d7847a2 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -720,6 +720,13 @@ static enum drm_gpu_sched_stat panfrost_job_timedout(struct drm_sched_job
>  	if (dma_fence_is_signaled(job->done_fence))
>  		return DRM_GPU_SCHED_STAT_NOMINAL;
>  
> +	synchronize_irq(pfdev->js->irq);

Can we add a comment here explaining why we're doing that?

> +
> +	if (dma_fence_is_signaled(job->done_fence)) {
> +		dev_warn(pfdev->dev, "unexpectedly high interrupt latency\n");
> +		return DRM_GPU_SCHED_STAT_NOMINAL;
> +	}
> +
>  	dev_err(pfdev->dev, "gpu sched timeout, js=%d, config=0x%x, status=0x%x, head=0x%x, tail=0x%x, sched_job=%p",
>  		js,
>  		job_read(pfdev, JS_CONFIG(js)),