linux-kernel - Re: [RFC PATCH v3 1/8] leds: add support for hardware driven LEDs

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Message-ID: <ece88816-ebe1-19d5-aa7d-16ad26121883@infradead.org>
Date:   Mon, 8 Nov 2021 22:16:51 -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 1/8] leds: add support for hardware driven LEDs

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 cd155ead8703..645940b78d81 100644
> --- a/Documentation/leds/leds-class.rst
> +++ b/Documentation/leds/leds-class.rst
> @@ -169,6 +169,34 @@ Setting the brightness to zero with brightness_set() callback function
>   should completely turn off the LED and cancel the previously programmed
>   hardware blinking function, if any.
>   
> +Hardware driven LEDs
> +===================================
> +
> +Some LEDs can be driven by hardware (for example a LED connected to
> +an ethernet PHY or an ethernet switch can be configured to blink on activity on
> +the network, which in software is done by the netdev trigger).
> +
> +To do such offloading, LED driver must support this and a supported trigger must
> +be used.
> +
> +LED driver should declare the correct blink_mode supported and should set the
> +blink_mode parameter to one of HARDWARE_CONTROLLED or SOFTWARE_HARDWARE_CONTROLLED.
> +The trigger will check this option and fail to activate if the blink_mode is not
> +supported. By default if a LED driver doesn't declare blink_mode, SOFTWARE_CONTROLLED
> +is assumed.
> +
> +The LED must implement 3 main API:

                                  APIs:

> +- hw_control_status(): This asks the LED driver if hardware mode is enabled
> +    or not. Triggers will check if the hardware mode is active and will try
> +    to offload their triggers if supported by the driver.
> +- hw_control_start(): This will simply enable the hardware mode for the LED.
> +- hw_control_stop(): This will simply disable the hardware mode for the LED.
> +    It's advised to the driver to put the LED in the old state but this is not

                     for the driver

> +    enforcerd and putting the LED off is also accepted.

        enforced

> +
> +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.
>   
>   Known Issues
>   ============
> diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
> index ed800f5da7d8..bd2b19cc77ec 100644
> --- a/drivers/leds/Kconfig
> +++ b/drivers/leds/Kconfig
> @@ -49,6 +49,17 @@ config LEDS_BRIGHTNESS_HW_CHANGED
>   
>   	  See Documentation/ABI/testing/sysfs-class-led for details.
>   
> +config LEDS_HARDWARE_CONTROL
> +	bool "LED Hardware Control support"
> +	help
> +	  This option enabled Hardware control support used by leds that

	              enables                                  LEDs

> +	  can be driven in hardware by using supported triggers.
> +
> +	  Hardware blink modes will be exposed by sysfs class in
> +	  /sys/class/leds based on the trigger currently active.
> +
> +	  If unsure, say Y.


-- 
~Randy