linux-kernel - Re: [PATCH v1 4/4] ARM: dts: add pwm node for r40.

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Date:   Mon, 15 Jan 2018 09:38:13 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Hao Zhang <hao5781286@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>, robh+dt@...nel.org,
        Mark Rutland <mark.rutland@....com>, linux@...linux.org.uk,
        Chen-Yu Tsai <wens@...e.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/Allwinner sunXi SoC support" 
        <linux-arm-kernel@...ts.infradead.org>, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v1 4/4] ARM: dts: add pwm node for r40.

Hi,

On Sun, Jan 14, 2018 at 02:43:39PM +0800, Hao Zhang wrote:
> 2018-01-11 20:47 GMT+08:00 Maxime Ripard <maxime.ripard@...e-electrons.com>:
> > On Thu, Jan 11, 2018 at 07:34:12PM +0800, hao_zhang wrote:
> >> This patch add pwm node for r40.
> >>
> >> Signed-off-by: hao_zhang <hao5781286@...il.com>
> >> ---
> >>  arch/arm/boot/dts/sun8i-r40.dtsi | 13 +++++++++++++
> >>  1 file changed, 13 insertions(+)
> >>
> >> diff --git a/arch/arm/boot/dts/sun8i-r40.dtsi b/arch/arm/boot/dts/sun8i-r40.dtsi
> >> index 173dcc1..84c963c 100644
> >> --- a/arch/arm/boot/dts/sun8i-r40.dtsi
> >> +++ b/arch/arm/boot/dts/sun8i-r40.dtsi
> >> @@ -295,6 +295,11 @@
> >>                               bias-pull-up;
> >>                       };
> >>
> >> +                     pwm_pins: pwm-pins {
> >> +                             pins = "PB2", "PB3";
> >> +                             function = "pwm";
> >> +                     };
> >> +
> >
> > Is it the only combination of pins that is usable?
> >
> > If so, you can add the pinctrl-0 property directly in the pwm nodes.
> >
> 
> There are 8 channel pwm of R40/V40/T3, the pins that can be configed
> to pwm are: PB2, PB3, PI20, PI21, PB20, PB21, PB9, PB10

And a single controller, or several of them?

> PB2, PB3 can be configed on bananapi-m2-ultra and on my T3 board,
> but the other pins is not exist on the board or some pin is confilct
> with other functions, so i just add PB2, PB3. but i think split it
> is better, just like this :
> 
> pwm0_pin: pwm0-pin {
>     pins = "PB2";
>     function = "pwm";
> };
> 
> pwm1_pin: pwm1-pin {
>     pins = "PB3";
>     function = "pwm";
> };

Yep, that would be better. If it's just a matter of channels, maybe we
can even name them pwm-ch0-pin and pwm-ch1-pin? That would be more
explicit.

> the node of pwm2~7 should also be added here?

If there's no users, no.

> On sun8i-r40-bananapi-m2-ultra.dts:
> because of the special customize board, i think just add pinctrl-0 = <&pwm0_pin>
> (PB3 I just use to test pwm channel 1)for bananapi-m2-ultra board is enough.
> 
> &pwm {
>     pinctrl-names = "default";
>     pinctrl-0 = <&pwm0_pin>;
>     status = "okay";
> };

It depends if that PWM is used as a PWM all the time (for example to
drive a backlight for a panel tied to the board), or if it's exported
through one of the generic pin headers, please leave it populated but
disabled (with a comment that it is exported on one of the pin of the
headers)

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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