linux-kernel - Re: [PATCH v2 3/4] media: platform: Add Renesas RZ/G2L MIPI CSI-2 receiver driver

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Date:   Thu, 22 Sep 2022 12:34:02 +0000
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Niklas Söderlund 
        <niklas.soderlund@...natech.se>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v2 3/4] media: platform: Add Renesas RZ/G2L MIPI CSI-2
 receiver driver

Hi Prabhakar,

On Thu, Sep 22, 2022 at 01:08:33PM +0100, Lad, Prabhakar wrote:
> > > * Switched to manually turn ON/OFF the clocks instead of pm_runtime so that
> > >   the mipi/dhpy initialization happens as per the HW manual
> >
> > That doesn't look right. The driver doesn't use runtime PM anymore, so
> > power domains may not be handled properly. What was the problem with
> > clock handling using runtime PM ?
> >
> If we use the runtime PM all the clocks will be turned ON when we call
> pm_runtime_resume_and_get() which I dont want to. As per the "Starting
> reception for MIPI CSI-2 Input" section 35.3.1 for example we first
> need to turn ON all the clocks and later further down the line we need
> to just turn OFF VCLK -> Enable Link -> turn ON VCLK. Due to such
> cases I have switched to individual clock handling.

If that is the case, then you should control just that clock directly,
outside runtime PM callbacks.

Runtime PM may be needed e.g. for resuming a parent device.

-- 
Regards,

Sakari Ailus