linux-kernel - Re: [PATCH 8/8] arm64: dts: renesas: salvator: add a connection from adv748x codec (HDMI input) to the R-Car SoC

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Date:   Mon, 2 Mar 2020 17:13:30 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alex Riesen <alexander.riesen@...itec.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        driverdevel <devel@...verdev.osuosl.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH 8/8] arm64: dts: renesas: salvator: add a connection from
 adv748x codec (HDMI input) to the R-Car SoC

Hi Alex,

On Mon, Mar 2, 2020 at 5:09 PM Alex Riesen <alexander.riesen@...itec.com> wrote:
> Geert Uytterhoeven, Mon, Mar 02, 2020 16:32:32 +0100:
> > > And this absence of documentation also means that whatever clocks (both input
> > > in "clocks=" and output in "#clock-cells") listed in a specific .dts are just
> > > an integration detail?
> >
> > No, the absence probably means that any clock-related properties in a .dts
> > file will just be ignored.
> >
> > Looking at the driver source, it indeed has no support related to clocks at all.
>
> ...
>
> > > Does this below makes more sense, than?
> > >
> > >     video-receiver@70 {
> > >         compatible = "adi,adv7482";
> > >         clocks = <&rcar_sound 3>;
> > >         clock-names = "clk-hdmi-video";
> > >         adv748x_mclk: mclk {
> > >             compatible = "fixed-clock";
> > >             #clock-cells =  <0>;
> > >             /* frequency hard-coded for illustration */
> > >             clock-frequency = <12288000>;
> > >             clock-output-names = "clk-hdmi-i2s-mclk";
> > >         };
> > >     };
> >
> > The #clock-cells should be in the main video-receiver node.
> > Probably there is more than one clock output, so #clock-cells may be 1?
>
> AFAICS, the device can provide only this one clock line (audio master clock
> for I2S output)... I shall re-check, just in case.
>
> > There is no need for a fixed-clock compatible, nor for clock-frequency
> > and clock-output-names.
> >
> > But most important: this should be documented in the adv748x DT bindings,
> > and implemented in the adv748x driver.
>
> So if the driver is to export that clock for the kernel (like in this case),
> it must implement its support?

Exactly.  Unless that pin is hardcoded to output a fixed clock, in which case
you can just override the existing audio_clk_c rate.

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