linux-kernel - Re: [RFC PATCH v2 1/4] media: dt-bindings: media: Document RZ/G2L CSI-2 block

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Date:   Fri, 21 Jan 2022 13:06:19 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [RFC PATCH v2 1/4] media: dt-bindings: media: Document RZ/G2L
 CSI-2 block

Hi Prabhakar,

On Fri, Jan 21, 2022 at 12:52 PM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
> On Fri, Jan 21, 2022 at 9:26 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Fri, Jan 21, 2022 at 2:06 AM Lad Prabhakar
> > <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> > > Document the CSI-2 block which is part of CRU found in Renesas
> > > RZ/G2L SoC.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Thanks for your patch!
> >
> > > ---
> > > Hi Geert/All,
> > >
> > > vclk and pclk clocks are shared with CRU both CSI and CRU driver are using
> > > pm_runtime. pclk clock is necessary for register access where as vclk clock
> > > is only used for calculations. So would you suggest passing vclk as part of
> >
> > What do you mean by "calculations"?
> To set the CSI2nMCT2 register bits (FRRSKW/FRRCLK), vclk clock rate is used.

Ah, clock rate calculations.  I (mis)understood that vclk clocked
a hardware calculation block, and was wondering what kind of heavy
calculations were involved ;-)

> > The bindings say this is the main clock?
> >
> That is because the RZG2L_clock_list_r02_02.xlsx mentions it as the main clock.
>
> > > clocks (as currently implemented) or pass the vclk clock rate as a dt property.
> >
> > Please do not specify clock rates in DT, but always pass clock
> > specifiers instead.
> > The clock subsystem handles sharing of clocks just fine.
> >
> Agreed.

So doing clk_get_rate() is fine.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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