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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 22 Sep 2022 14:51:27 +0200
Message-ID: <CAMuHMdXKz56jxw56fXa7CMh_y4MVYiUT25dqRntJw6481s1FWw@mail.gmail.com>
Subject: Re: [PATCH v2 3/4] media: platform: Add Renesas RZ/G2L MIPI CSI-2
 receiver driver
To:     Sakari Ailus <sakari.ailus@linux.intel.com>,
        "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Jacopo Mondi <jacopo@jmondi.org>,
        =?UTF-8?Q?Niklas_S=C3=B6derlund?= <niklas.soderlund@ragnatech.se>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        linux-media@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
        Biju Das <biju.das.jz@bp.renesas.com>
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On Thu, Sep 22, 2022 at 2:34 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
> 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.

Exactly.
So probably you should not consider R9A07G044_CRU_VCLK a PM clock,
i.e. you need changes to rzg2l_cpg_is_pm_clk() to exclude it.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds