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

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Message-ID: <YYk/Pbm9ZZ/Ikckg@Ansuel-xps.localdomain>
Date:   Mon, 8 Nov 2021 16:16:13 +0100
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
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

On Mon, Nov 08, 2021 at 03:04:23PM +0100, Andrew Lunn wrote:
> > +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().
> 

To not add too much function to the struct, can we introduce one
function that both enable and disable the hw mode?

> 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.
> 

So we have PHYs that can only work in offload or off. Correct?

> 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? 
>

I think it should be put off. Do you agree? (also the brightness should
be set to 0 in this case)

>      Andrew

-- 
	Ansuel