Re: [PATCH] leds: pwm: Allow automatic labels for DT based devices

[Jacek Anaszewski]

Hi Alexander,

On 8/28/20 9:00 AM, Alexander Dahl wrote:
> Hello Jacek,
>
> Am Donnerstag, 27. August 2020, 23:28:45 CEST schrieb Jacek Anaszewski:
> > On 8/26/20 11:37 AM, Alexander Dahl wrote:
> > > From: Alexander Dahl <post@xxxxxxxxxxx>
> > >
> > > If LEDs are configured through device tree and the property 'label' is
> > > omitted, the label is supposed to be generated from the properties
> > > 'function' and 'color' if present.  While this works fine for e.g. the
> > > 'leds-gpio' driver, it did not for 'leds-pwm'.
> > >
> > > The reason is, you get this label naming magic only if you add a LED
> > > device through 'devm_led_classdev_register_ext()' and pass a pointer to
> > > the current device tree node.  The approach to fix this was adopted from
> > > the 'leds-gpio' driver.
> > >
> > > For the following node from dts the LED appeared as 'led5' in sysfs
> > > before and as 'red:debug' after this change.
> > >
> > >           pwm_leds {
> > >           
> > >                   compatible = "pwm-leds";
> > >                   
> > >                   led5 {
> > >                   
> > >                           function = LED_FUNCTION_DEBUG;
> > >                           color = <LED_COLOR_ID_RED>;
> > >                           pwms = <&pwm0 2 10000000 0>;
> > >                           max-brightness = <127>;
> > >                           
> > >                           linux,default-trigger = "heartbeat";
> > >                           panic-indicator;
> > >                   
> > >                   };
> > >           
> > >           };
> > >
> > > Signed-off-by: Alexander Dahl <post@xxxxxxxxxxx>
> > > ---
> > >
> > > Notes:
> > >       v1: based on v5.9-rc2, backport on v5.4.59 also works
> > >    
> > >    drivers/leds/leds-pwm.c | 9 ++++++++-
> > >    1 file changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
> > > index ef7b91bd2064..a27a1d75a3e9 100644
> > > --- a/drivers/leds/leds-pwm.c
> > > +++ b/drivers/leds/leds-pwm.c
> > > @@ -65,6 +65,7 @@ static int led_pwm_add(struct device *dev, struct
> > > led_pwm_priv *priv,>
> > >    		       struct led_pwm *led, struct fwnode_handle *fwnode)
> > >    
> > >    {
> > >    
> > >    	struct led_pwm_data *led_data = &priv->leds[priv->num_leds];
> > >
> > > +	struct led_init_data init_data = {};
> > >
> > >    	int ret;
> > >    	
> > >    	led_data->active_low = led->active_low;
> > >
> > > @@ -90,7 +91,13 @@ static int led_pwm_add(struct device *dev, struct
> > > led_pwm_priv *priv,>
> > >    	pwm_init_state(led_data->pwm, &led_data->pwmstate);
> > >
> > > -	ret = devm_led_classdev_register(dev, &led_data->cdev);
> > > +	if (fwnode) {
> > > +		init_data.fwnode = fwnode;
> > > +		ret = devm_led_classdev_register_ext(dev, &led_data->cdev,
> > > +						     &init_data);
> > > +	} else {
> > > +		ret = devm_led_classdev_register(dev, &led_data->cdev);
> > > +	}
> > >
> > >    	if (ret) {
> > >    	
> > >    		dev_err(dev, "failed to register PWM led for %s: %d\n",
> > >    		
> > >    			led->name, ret);
> >
> > This part looks good, but corresponding update of
> > Documentation/devicetree/bindings/leds/leds-pwm.txt is needed as well.
>
> I'm not sure, what needs updating. The properties 'function' and 'color' are
> already documented in Documentation/devicetree/bindings/leds/common.yaml … the
> only thing I can think of here is updating the examples? That would be nice,
> as would be updating to yaml, but I don't see the strong relation, yet.

It is necessary to tell the user that given driver is capable of
utilizing a property. I thought of something like in commit [0].

> > It would be good to switch to yaml by this occassion.
>
> Is there some guidance on that in general?

I am not aware of, but surely sooner or later all bindings will
need to be unified. Touching the file is always a good opportunity
to address that. It's up to you, though.

[0] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/Documentation/devicetree/bindings/leds/leds-lm3692x.txt?id=4dcbc8f8c59f4b618d651f5ba884ee5bf562c8de

--
Best regards,
Jacek Anaszewski