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

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Date:   Tue, 9 Nov 2021 21:34:23 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     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 Tue, Nov 09, 2021 at 03:26:01AM +0100, Ansuel Smith wrote:
> 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:
> - trigger_offload_status(): This asks the LED driver if offload mode is
>     enabled or not.
>     Triggers will check if the offload mode is supported and will be
>     activated accordingly. If the trigger can't run in software mode,
>     return -EOPNOTSUPP as the blinking can't be simulated by software.

I don't understand this last part. The LED controller is not
implementing software mode, other than providing a method to manually
turn the LED on and off. And there is a well defined call for that. If
that call is a NULL, it is clear it is not implemented. There is no
need to ask the driver.

     Andrew