linux-kernel - Re: [PATCH v1] drm/panfrost: Sync IRQ by job's timeout handler

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Message-ID: <80de081a-e443-85a2-1a61-6a8885e8d529@collabora.com>
Date:   Mon, 17 Jul 2023 10:20:02 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Boris Brezillon <boris.brezillon@...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 v1] drm/panfrost: Sync IRQ by job's timeout handler

Hi,

On 7/17/23 10:05, Boris Brezillon wrote:
> Hi Dmitry,
> 
> On Mon, 17 Jul 2023 09:52:54 +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.
> 
> Feels like the problem should be fixed in the HDMI encoder driver
> instead, so it doesn't stall the whole system when processing its
> IRQs (use threaded irqs, maybe). I honestly don't think blocking in the
> job timeout path to flush IRQs is a good strategy.

The syncing is necessary to have for correctness regardless of whether
it's HDMI problem or something else, there could be other reasons for
CPU to delay IRQ processing. It's wrong to say that hw is hung, while
it's not.

-- 
Best regards,
Dmitry