linux-kernel - Re: [PATCH v4 1/3] dt-bindings: pwm: add MediaTek display PWM bindings

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Message-ID: <CAGS+omAZismuEYXsUkHEAec4xF+KRWm62AuCUmrmso6p+DKQ4Q@mail.gmail.com>
Date:	Thu, 9 Jul 2015 12:47:46 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	YH Huang <yh.huang@...iatek.com>
Cc:	Matthias Brugger <matthias.bgg@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	Thierry Reding <thierry.reding@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>, linux-pwm@...r.kernel.org,
	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	srv_heupstream <srv_heupstream@...iatek.com>,
	linux-mediatek@...ts.infradead.org,
	Sascha Hauer <kernel@...gutronix.de>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>
Subject: Re: [PATCH v4 1/3] dt-bindings: pwm: add MediaTek display PWM bindings

On Thu, Jul 9, 2015 at 10:45 AM, YH Huang <yh.huang@...iatek.com> wrote:
>
> On Wed, 2015-07-08 at 20:11 +0800, Daniel Kurtz wrote:
> > On Mon, Jul 6, 2015 at 9:29 PM, YH Huang <yh.huang@...iatek.com> wrote:
> > > Document the device-tree binding of MediatTek display PWM.
> > > The PWM has one channel to control the backlight brightness for display.
> > > It supports MT8173 and MT6595.
> > >
> > > Signed-off-by: YH Huang <yh.huang@...iatek.com>
> > > ---
> > >  .../devicetree/bindings/pwm/pwm-mtk-disp.txt       | 24 ++++++++++++++++++++++
> > >  1 file changed, 24 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt b/Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt
> > > new file mode 100644
> > > index 0000000..757b974
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt
> > > @@ -0,0 +1,24 @@
> > > +MediaTek display PWM controller
> > > +
> > > +Required properties:
> > > + - compatible: should be "mediatek,<name>-disp-pwm"
> > > +   - "mediatek,mt8173-disp-pwm": found on mt8173 SoC
> > > +   - "mediatek,mt6595-disp-pwm": found on mt6595 SoC
> > > + - reg: physical base address and length of the controller's registers
> > > + - #pwm-cells: must be 2. See pwm.txt in this directory for a description of
> > > +   the cell format
> > > + - clocks: phandle and clock specifier of the PWM reference clock
> > > + - clock-names: must contain the following
> > > +   - "main": clock used to generate PWM signals
> > > +   - "mm": sync signals from the modules of mmsys
> > > +
> > > +Example:
> > > +       pwm0: pwm@...1e000 {
> > > +               compatible = "mediatek,mt8173-disp-pwm",
> > > +                            "mediatek,mt6595-disp-pwm";
> > > +               reg = <0 0x1401e000 0 0x1000>;
> > > +               #pwm-cells = <2>;
> > > +               clocks = <&mmsys CLK_MM_DISP_PWM026M>,
> > > +                        <&mmsys CLK_MM_DISP_PWM0MM>;
> > > +               clock-names = "main", "mm";
> >
> > Should we include the pinctrl settings here to enable the PWM output?
> >
>
> Since we use pwm-backlight driver to control backlight, we should enable
> PWM output in the backlight node.
>
> Ref:
> https://www.kernel.org/doc/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
>

The pwm-backlight binding specifies which pwm the backlight driver
should use, and how to use it.

I believe actually configuring the output pin for the pwm via pinctl
belongs to the pwm binding.

Regards,
0Dan

>
> Regards,
> YH Huang
>
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