linux-kernel - Re: [PATCH] media: ov5640: use pm_runtime_force

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Message-ID: <ZQHU+LA+BEB7jzx1@valkosipuli.retiisi.eu>
Date:   Wed, 13 Sep 2023 15:27:52 +0000
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Andrey Skvortsov <andrej.skvortzov@...il.com>
Cc:     Steve Longerbeam <slongerbeam@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jarrah Gosbell <kernel@...ef.tools>,
        Arnaud Ferraris <arnaud.ferraris@...labora.com>,
        laurent.pinchart@...asonboard.com
Subject: Re: [PATCH] media: ov5640: use pm_runtime_force_suspend/resume for
 system suspend

Hi Andrey,

On Fri, Aug 18, 2023 at 08:34:16PM +0300, Andrey Skvortsov wrote:
> If system was suspended while camera sensor was used, data and
> interrupts were still coming from sensor and that caused unstable
> system. Sometimes system hanged during a resume. Use
> pm_runtime_force_* helpers in order to support system suspend.
> 
> Signed-off-by: Andrey Skvortsov <andrej.skvortzov@...il.com>

Thanks for the patch.

It's not been documented really how system suspend and resume should
work for complex cameras. But I don't think it can be done by drivers
separately as the CSI-2 bus initialisation requires actions from both
sender and receiver drivers, at particular points of time.

So I think we'll need to initiate this from the driver handling DMA, just
as starting and stopping streaming. Even then, there needs to be a
certainty that the sensor device has resumed before streaming is started. I
recall Laurent suggested device links for that purpose, but I don't think
any work has been done to implement it that way.

-- 
Kind regards,

Sakari Ailus