linux-kernel - Re: [RFC PATCH v3 2/8] leds: add function to configure hardware controlled LED

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Date:   Mon, 8 Nov 2021 22:12:05 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Ansuel Smith <ansuelsmth@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>, Pavel Machek <pavel@....cz>,
        John Crispin <john@...ozen.org>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-leds@...r.kernel.org,
        Marek Behún <kabel@...nel.org>
Subject: Re: [RFC PATCH v3 2/8] leds: add function to configure hardware
 controlled LED

On 11/8/21 6:26 PM, Ansuel Smith wrote:
> diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
> index 645940b78d81..efd2f68c46a7 100644
> --- a/Documentation/leds/leds-class.rst
> +++ b/Documentation/leds/leds-class.rst
> @@ -198,6 +198,31 @@ With HARDWARE_CONTROLLED blink_mode hw_control_status/start/stop is optional
>   and any software only trigger will reject activation as the LED supports only
>   hardware mode.
>   
> +A trigger once he declared support for hardware controlled blinks, will use the function

Maybe this:
    Once a trigger has declared support for hardware-controller blinks, it will us the function

> +hw_control_configure() provided by the driver to check support for a particular blink mode.
> +This function passes as the first argument (flag) a u32 flag.
> +The second argument (cmd) of hw_control_configure() method can be used to do various
> +operations for the specific blink mode. We currently support ENABLE, DISABLE, READ, ZERO
> +and SUPPORTED to enable, disable, read the state of the blink mode, ask the LED
> +driver if it does supports the specific blink mode and to reset any blink mode active.
> +
> +In ENABLE/DISABLE hw_control_configure() should configure the LED to enable/disable the
> +requested blink mode (flag).
> +In READ hw_control_configure() should return 0 or 1 based on the status of the requested
> +blink mode (flag).
> +In SUPPORTED hw_control_configure() should return 0 or 1 if the LED driver supports the
> +requested blink mode (flags) or not.
> +In ZERO hw_control_configure() should return 0 with success operation or error.
> +
> +The unsigned long flag is specific to the trigger and change across them. It's in the LED

                                                          changes

> +driver interest know how to elaborate this flag and to declare support for a

    driver's interest to know how to

> +particular trigger. For this exact reason explicit support for the specific
> +trigger is mandatory or the driver returns -EOPNOTSUPP if asked to enter offload mode
> +with a not supported trigger.
> +If the driver returns -EOPNOTSUPP on hw_control_configure(), the trigger activation will
> +fail as the driver doesn't support that specific offload trigger or doesn't know
> +how to handle the provided flags.


-- 
~Randy