linux-kernel - Re: [PATCH v4] drm/panfrost: Sync IRQ by job's timeout handler

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Date:   Thu, 10 Aug 2023 08:42:19 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        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 v4] drm/panfrost: Sync IRQ by job's timeout handler

On Mon,  7 Aug 2023 03:04:44 +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.
> 
> Reviewed-by: Steven Price <steven.price@....com>
> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com> # MediaTek MT8192 and MT8195 Chromebooks
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

Queued to drm-misc-next.

Thanks,

Boris

> ---
> 
> Changelog:
> 
> v4: - Improved comment like was suggested by Boris and added his r-b.
> 
> v3: - Added comment to the code as was suggested by Boris
> 
>     - Added r-b/t-b from Steven and Angelo
> 
> 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 | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index dbc597ab46fb..db6d9a17004f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -720,6 +720,22 @@ 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;
>  
> +	/*
> +	 * Panfrost IRQ handler may take a long time to process an interrupt
> +	 * if there is another IRQ handler hogging the processing.
> +	 * For example, the HDMI encoder driver might be stuck in the IRQ
> +	 * handler for a significant time in a case of bad cable connection.
> +	 * In order to catch such cases and not report spurious Panfrost
> +	 * job timeouts, synchronize the IRQ handler and re-check the fence
> +	 * status.
> +	 */
> +	synchronize_irq(pfdev->js->irq);
> +
> +	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)),