linux-kernel - Re: [PATCH v7 2/2] Driver for ON Semi AR0521 camera sensor

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Message-ID: <m3czj57tmf.fsf@t19.piap.pl>
Date:   Tue, 01 Mar 2022 13:19:20 +0100
From:   Krzysztof Hałasa <khalasa@...p.pl>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sakari Ailus <sakari.ailus@....fi>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v7 2/2] Driver for ON Semi AR0521 camera sensor

Jacopo Mondi <jacopo@...ndi.org> writes:

>> They can. It appears, though, that clusters aren't about controls which
>> can't change independently. Both of the two are written to the hardware
>> at the same time, which appears to be a valid reason to combine them
>> into a cluster.
>
> Is there a reason to write them to hw at the same time ? :)

Sure, they are written in a single merged burst on I2C.

> As it doesn't seem to me you access registers during probe (to
> identify the sensor in example) there's no need to power up the device
> during probe, but should be enough to let runtime_pm do so when
> requested.

Yes, in fact I never try to read anything from the sensor :-)
Unfortunately I'm not sure how to initialize the (possibly nonexistent)
PM without powering it up, cleanly, in all kernel configs. I mean, I can
check if PM failed and power it up "by hand", but it's a bit messy.

Suggestions are welcome, though.
-- 
Krzysztof "Chris" Hałasa

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