linux-kernel - Re: [PATCH v6 2/3] media: i2c: imx274: Remove stop stream i2c writes during remove

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Date:   Thu, 24 Sep 2020 12:09:22 +0200
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, hverkuil@...all.nl,
        jacopo+renesas@...ndi.org, leonl@...pardimaging.com,
        robh+dt@...nel.org, lgirdwood@...il.com, broonie@...nel.org,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/3] media: i2c: imx274: Remove stop stream i2c writes
 during remove

On 22/09/20 10:47, Sakari Ailus wrote:
> Hi Luca,
> 
> On Tue, Sep 22, 2020 at 10:09:33AM +0200, Luca Ceresoli wrote:
>> Hi,
>>
>> On 21/09/20 23:39, Sowjanya Komatineni wrote:
>>> Sensor should already be in standby during remove and there is no
>>> need to configure sensor registers for stream stop.
>>
>> I beg your pardon for the newbie question: does the V4L2 framework
>> guarantee that the stream is stopped (.s_stream(..., 0)) before removing
>> the driver?
> 
> It doesn't. That's however one of the lesser concerns, and I don't think
> it'd help if drivers tried to prepare for that.

Thanks for the clarification.

I've been working with hardware where the sensor is always powered. In
this case, and with this patch applied, the sensor would keep producing
frames after driver removal. This looks wrong, unless I'm overlooking
something.

BTW at first sight it looks like the framework should take care of
stopping the stream before removal, not the individual drivers, but
maybe there are good reasons this is not done?

-- 
Luca