netdev - Re: [RFC PATCH v2 1/5] leds: trigger: add API for HW offloading of triggers

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Date:   Mon, 8 Nov 2021 15:04:23 +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 v2 1/5] leds: trigger: add API for HW offloading of
 triggers

> +static inline int led_trigger_offload(struct led_classdev *led_cdev)
> +{
> +	int ret;
> +
> +	if (!led_cdev->trigger_offload)
> +		return -EOPNOTSUPP;
> +
> +	ret = led_cdev->trigger_offload(led_cdev, true);
> +	led_cdev->offloaded = !ret;
> +
> +	return ret;
> +}
> +
> +static inline void led_trigger_offload_stop(struct led_classdev *led_cdev)
> +{
> +	if (!led_cdev->trigger_offload)
> +		return;
> +
> +	if (led_cdev->offloaded) {
> +		led_cdev->trigger_offload(led_cdev, false);
> +		led_cdev->offloaded = false;
> +	}
> +}
> +#endif

I think there should be two calls into the cdev driver, not this
true/false parameter. trigger_offload_start() and
trigger_offload_stop().

There are also a number of PHYs which don't allow software blinking of
the LED. So for them, trigger_offload_stop() is going to return
-EOPNOTSUPP. And you need to handle that correctly.

It would be go to also document the expectations of
trigger_offload_stop(). Should it leave the LED in whatever state it
was, or force it off? 

     Andrew