[PATCH 1/2] ARM: dts: r8a7740: Add LCDC nodes

[Geert Uytterhoeven]

Hi Laurent,

On Fri, Jun 23, 2023 at 5:12 PM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
> On Fri, Jun 23, 2023 at 05:07:44PM +0200, Geert Uytterhoeven wrote:
> > On Fri, Jun 23, 2023 at 3:03 PM Laurent Pinchart wrote:
> > > On Thu, Jun 22, 2023 at 11:23:14AM +0200, Geert Uytterhoeven wrote:
> > > > Add device nodes for the two LCD Controllers (LCDC) on the R-Mobile A1
> > > > SoC, and for the two optional external LCDL clock inputs.
> > > >
> > > > Note that the HDMI clock for LCDC1 is not added, as this clock is not
> > > > yet supported.
> > > >
> > > > Based on a patch by Laurent Pinchart adding the first LCDC device node.
> > > >
> > > > Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
> > > > ---
> > > > Changes compared to Laurent's original:
> > > >   - Add lcdc0 label,
> > > >   - Rename node from display to lcdc-controller,
> > > >   - Rename compatible value from "renesas,lcdc-r8a7740" to
> > > >     "renesas,r8a7740-lcdc",
> > > >   - Correct syntax of reg property,
> > > >   - Use GIC_SPI macro,
> > > >   - Add more clocks,
> > > >   - Add power-domains property,
> > > >   - Add status disabled,
> > > >   - Remove second port from lcdc0, as only lcdc1 has an HDMI port,
> > > >   - Add lcdc1 device node.
> > > > ---
> > > >  arch/arm/boot/dts/r8a7740.dtsi | 65 ++++++++++++++++++++++++++++++++++
> > > >  1 file changed, 65 insertions(+)
> > > >
> > > > diff --git a/arch/arm/boot/dts/r8a7740.dtsi b/arch/arm/boot/dts/r8a7740.dtsi
> > > > index 1b2cf5fa322b2985..55884ec701f8dab4 100644
> > > > --- a/arch/arm/boot/dts/r8a7740.dtsi
> > > > +++ b/arch/arm/boot/dts/r8a7740.dtsi

> > > > @@ -474,6 +529,16 @@ fsibck_clk: fsibck {
> > > >                       #clock-cells = <0>;
> > > >                       clock-frequency = <0>;
> > > >               };
> > > > +             lcdlclk0_clk: lcdlclk0 {
> > > > +                     compatible = "fixed-clock";
> > > > +                     #clock-cells = <0>;
> > > > +                     clock-frequency = <0>;
> > > > +             };
> > > > +             lcdlclk1_clk: lcdlclk1 {
> > > > +                     compatible = "fixed-clock";
> > > > +                     #clock-cells = <0>;
> > > > +                     clock-frequency = <0>;
> > > > +             };
> > >
> > > The clock frequency seems quite low :-) As far as I understand, there
> > > are the clocks fed to the external LCDLCLK pins. They belong to the
> > > board DTS, not here. If a board doesn't provide an external clock, the
> > > clock should simply be ommitted. The driver must thus treat it as
> > > optional.
> >
> > Usually, we do provide clock nodes with a zero rate in the SoC-specific
> > .dtsi for optional clocks.
>
> Who is "we" ? Is that a kernel-wide practice ? For rcar-du that's not
> the case as far as I can tell.

"We" do for external CAN, SCIF, Audio, PCI, USB, ... clocks on R-Car.
Indeed not for DU...

It seems to be common on other platform, too:

    git grep "clock-frequency = <0>;"

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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