linux-kernel - Re: [PATCH v3 1/6] docs: firmware-guide: ACPI: Add a PWM example

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Date:   Mon, 7 Jun 2021 14:38:26 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Flavio Suligoi <f.suligoi@...m.it>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Lee Jones <lee.jones@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v3 1/6] docs: firmware-guide: ACPI: Add a PWM example

On Mon, Jun 7, 2021 at 2:24 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> When PWM support for ACPI has been added into the kernel, it missed
> the documentation update. Hence update documentation here.
>
> Fixes: 4a6ef8e37c4d ("pwm: Add support referencing PWMs from ACPI")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

and I'm assuming this to go in via PWM.

> ---
> v3: despite flags being optional, don't alter it in the documentation
> v2: updated example to use 600 ms instead of 600 us (looks saner)
>  .../firmware-guide/acpi/enumeration.rst       | 32 +++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst
> index 9f0d5c854fa4..f588663ba906 100644
> --- a/Documentation/firmware-guide/acpi/enumeration.rst
> +++ b/Documentation/firmware-guide/acpi/enumeration.rst
> @@ -258,6 +258,38 @@ input driver::
>                 .id_table       = mpu3050_ids,
>         };
>
> +Reference to PWM device
> +=======================
> +
> +Sometimes a device can be a consumer of PWM channel. Obviously OS would like
> +to know which one. To provide this mapping the special property has been
> +introduced, i.e.::
> +
> +    Device (DEV)
> +    {
> +        Name (_DSD, Package ()
> +        {
> +            ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> +            Package () {
> +                Package () { "compatible", Package () { "pwm-leds" } },
> +                Package () { "label", "alarm-led" },
> +                Package () { "pwms",
> +                    Package () {
> +                        "\\_SB.PCI0.PWM",  // <PWM device reference>
> +                        0,                 // <PWM index>
> +                        600000000,         // <PWM period>
> +                        0,                 // <PWM flags>
> +                    }
> +                }
> +            }
> +
> +        })
> +        ...
> +
> +In the above example the PWM-based LED driver references to the PWM channel 0
> +of \_SB.PCI0.PWM device with initial period setting equal to 600 ms (note that
> +value is given in nanoseconds).
> +
>  GPIO support
>  ============
>
> --
> 2.30.2
>