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Date:   Tue, 1 Aug 2023 09:50:22 +0200
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Rob Herring <robh@kernel.org>,
        Steven Price <steven.price@arm.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com
Subject: Re: [PATCH v3] drm/panfrost: Sync IRQ by job's timeout handler
Message-ID: <20230801095022.2c5e66d6@collabora.com>
In-Reply-To: <20230801001427.176981-1-dmitry.osipenko@collabora.com>
References: <20230801001427.176981-1-dmitry.osipenko@collabora.com>
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On Tue,  1 Aug 2023 03:14:27 +0300
Dmitry Osipenko <dmitry.osipenko@collabora.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@arm.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> # MediaTek MT8192 and MT8195 Chromebooks:
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

Just a couple nits below.

> ---
> 
> Changelog:
> 
> 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 | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index dbc597ab46fb..ea1149354f9d 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -720,6 +720,21 @@ 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 long time to process if there is

				^ may take a long time to process an
	interrupt if there is ...

> +	 * another IRQ handler hogging the processing. For example, HDMI
> +	 * may stuck in IRQ handler for a significant time in a case of bad

	For example, the HDMI encoder driver might be stuck in the IRQ
	handler ...

> +	 * 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)),