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

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Message-ID: <ZQIgDb0usm768umH@skv.local>
Date:   Wed, 13 Sep 2023 23:48:13 +0300
From:   Andrey Skvortsov <andrej.skvortzov@...il.com>
To:     Sakari Ailus <sakari.ailus@....fi>
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 Sakari,

On 23-09-13 15:27, Sakari Ailus wrote:
> 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.

Thanks for the review.

I've tested this on PinePhone A64. It uses DVP, maybe because of that
system suspend/resume worked good in my case.
Originally I've implemented system suspend/resume similar to this [1]
or [2] as I've seen this approach in other mainlined drivers. But some
drivers reuse pm_runtime_force_* helpers, so I've went with this.

Do you think it would be better to use something like [2] until there
is better well defined way for system suspend/resume for complex cameras?

> 
> 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.

1. https://salsa.debian.org/Mobian-team/devices/kernels/sunxi64-linux/-/blob/mobian-6.1/debian/patches/camera/0076-media-gc2145-implement-system-suspend.patch
2. https://elixir.bootlin.com/linux/latest/source/drivers/media/i2c/imx219.c#L1159

-- 
Best regards,
Andrey Skvortsov