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

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Message-ID: <CA+V-a8u=WE1roHfr_6dsB85ajKtQx-uzJn82tsekvP2GtrOkqQ@mail.gmail.com>
Date:   Thu, 22 Sep 2022 14:12:40 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.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 Sakari,

On Thu, Sep 22, 2022 at 1:34 PM Sakari Ailus
<sakari.ailus@...ux.intel.com> wrote:
>
> 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.
>
OK, I'll move the control outside runtime PM.

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

Cheers,
Prabhakar