linux-kernel - Re: [PATCH v1 4/4] riscv: dts: sifive unmatched: Add PWM controlled LEDs

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Date:   Wed, 6 Jul 2022 09:56:16 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Vincent Pelletier <plr.vincent@...il.com>,
        Bin Meng <bin.meng@...driver.com>,
        Aurelien Jarno <aurelien@...el32.net>,
        Ron Economos <w6rz@...cast.net>,
        Qiu Wenbo <qiuwenbo@...inos.com.cn>,
        Stephen L Arnold <nerdboy@...too.org>,
        Jianlong Huang <jianlong.huang@...rfivetech.com>,
        Mark Kettenis <kettenis@...nbsd.org>,
        Sven Schwermer <sven.schwermer@...ruptive-technologies.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        David Abdurachmanov <davidlt@...osinc.com>,
        linux-leds <linux-leds@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v1 4/4] riscv: dts: sifive unmatched: Add PWM controlled LEDs

Hi Emil,

On Tue, Jul 5, 2022 at 11:01 PM Emil Renner Berthing
<emil.renner.berthing@...onical.com> wrote:
> This adds the two PWM controlled LEDs to the HiFive Unmatched device
> tree. D12 is just a regular green diode, but D2 is an RGB diode with 3
> PWM inputs controlling the three different colours.
>
> Signed-off-by: Emil Renner Berthing <emil.renner.berthing@...onical.com>

Thanks for your patch!

> --- a/arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dts
> +++ b/arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dts
> @@ -44,6 +46,46 @@ gpio-poweroff {
>                 compatible = "gpio-poweroff";
>                 gpios = <&gpio 2 GPIO_ACTIVE_LOW>;
>         };
> +
> +       led-controller-1 {
> +               compatible = "pwm-leds";
> +
> +               led-d12 {
> +                       pwms = <&pwm0 0 7812500 PWM_POLARITY_INVERTED>;
> +                       active-low;

The first thing that came into my mind was "why not drop the
PWM_POLARITY_INVERTED flag instead?".

But it turns out drivers/pwm/pwm-sifive.c does not support
non-inverted PWMs, and returns -EINVAL if PWM_POLARITY_INVERSED
(no typo) is not set.  I think it would be good if
Documentation/devicetree/bindings/pwm/pwm-sifive.yaml would mention
this limitation, and perhaps even enforce it, if possible?

I didn't check this against the schematics, but the generic structure
LGTM, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

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