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

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Message-ID: <YyxoYSnj9llox5l1@pendragon.ideasonboard.com>
Date:   Thu, 22 Sep 2022 16:51:29 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.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>,
        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

On Thu, Sep 22, 2022 at 02:27:15PM +0100, Lad, Prabhakar wrote:
> On Thu, Sep 22, 2022 at 1:51 PM Geert Uytterhoeven wrote:
> > On Thu, Sep 22, 2022 at 2:34 PM Sakari Ailus 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.
> 
> Thanks for the pointer. In that case we will have to consider
> R9A07G044_CRU_VCLK and R9A07G044_CRU_SYSCLK as not PM clocks.

I like when patch review discussions continue on the list without my
involvement, and the end result is exactly what I would have advised :-)

> Does the below sound good?
> - DEF_NO_PM() macro
> - bool is_pm_clk in struct rzg2l_mod_clk.
> 
> I still have to implement it, just wanted your opinion beforehand.

Looks good to me, but I'm no expert in this area. I trust Geert's
advice.

-- 
Regards,

Laurent Pinchart