linux-kernel - Re: [PATCH v7 01/11] leds: add support for hardware driven LEDs

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Message-ID: <639ca0a4.050a0220.99395.8fd3@mx.google.com>
Date:   Fri, 16 Dec 2022 17:45:25 +0100
From:   Christian Marangi <ansuelsmth@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.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,
        Tim Harvey <tharvey@...eworks.com>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Marek Behún <kabel@...nel.org>
Subject: Re: [PATCH v7 01/11] leds: add support for hardware driven LEDs

On Thu, Dec 15, 2022 at 04:13:03PM +0000, Russell King (Oracle) wrote:
> Hi Christian,
> 
> Thanks for the patch.
> 
> I think Andrew's email is offline at the moment.
>

Notice by gmail spamming me "I CAN'T SEND IT AHHHHH"
Holidy times I guess?

> On Thu, Dec 15, 2022 at 12:54:28AM +0100, Christian Marangi wrote:
> > +static bool led_trigger_is_supported(struct led_classdev *led_cdev,
> > +				     struct led_trigger *trigger)
> > +{
> > +	switch (led_cdev->blink_mode) {
> > +	case SOFTWARE_CONTROLLED:
> > +		if (trigger->supported_blink_modes == HARDWARE_ONLY)
> > +			return 0;
> > +		break;
> > +	case HARDWARE_CONTROLLED:
> > +		if (trigger->supported_blink_modes == SOFTWARE_ONLY)
> > +			return 0;
> > +		break;
> > +	case SOFTWARE_HARDWARE_CONTROLLED:
> > +		break;
> > +	default:
> > +		return 0;
> > +	}
> > +
> > +	return 1;
> 
> Should be returning true/false. I'm not sure I'm a fan of the style of
> this though - wouldn't the following be easier to read?
> 
> 	switch (led_cdev->blink_mode) {
> 	case SOFTWARE_CONTROLLED:
> 		return trigger->supported_blink_modes != HARDWARE_ONLY;
> 
> 	case HARDWARE_CONTROLLED:
> 		return trigger->supported_blink_modes != SOFTWARE_ONLY;
> 
> 	case SOFTWARE_HARDWARE_CONTROLLED:
> 		return true;
> 	}
> ?

Much better!

> 
> Also, does it really need a default case - without it, when the
> led_blink_modes enum is expanded and the switch statement isn't
> updated, we'll get a compiler warning which will prompt this to be
> updated - whereas, with a default case, it won't.
> 

I added the default just to mute some compiler warning. But guess if
every enum is handled the warning should not be reported.

> > @@ -188,6 +213,10 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
> >  		led_set_brightness(led_cdev, LED_OFF);
> >  	}
> >  	if (trig) {
> > +		/* Make sure the trigger support the LED blink mode */
> > +		if (!led_trigger_is_supported(led_cdev, trig))
> > +			return -EINVAL;
> 
> Shouldn't validation happen before we start taking any actions? In other
> words, before we remove the previous trigger?
> 

trigger_set first remove any trigger and set the led off. Then apply the
new trigger. So the validation is done only when a trigger is actually
applied. Think we should understand the best case here.

> > @@ -350,12 +381,26 @@ static inline bool led_sysfs_is_disabled(struct led_classdev *led_cdev)
> >  
> >  #define TRIG_NAME_MAX 50
> >  
> > +enum led_trigger_blink_supported_modes {
> > +	SOFTWARE_ONLY = SOFTWARE_CONTROLLED,
> > +	HARDWARE_ONLY = HARDWARE_CONTROLLED,
> > +	SOFTWARE_HARDWARE = SOFTWARE_HARDWARE_CONTROLLED,
> 
> I suspect all these generic names are asking for eventual namespace
> clashes. Maybe prefix them with LED_ ?

Agree they are pretty generic so I can see why... My only concern was
making them too long... Maybe reduce them to SW or HW? LEDS_SW_ONLY...
LEDS_SW_CONTROLLED?

> 
> Thanks.
> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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