linux-kernel - Re: [PATCH v2] leds: pwm: add support for default-state device property

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Message-ID: <9e4bd43d14d00266bab4695dd37019bb1a103dd2.camel@diehl.com>
Date:   Wed, 11 Mar 2020 06:45:30 +0000
From:   Denis Osterland-Heim <denis.osterland@...hl.com>
To:     "dmurphy@...com" <dmurphy@...com>, "pavel@....cz" <pavel@....cz>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jacek.anaszewski@...il.com" <jacek.anaszewski@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2] leds: pwm: add support for default-state device
 property

Hi Jacek,

Am Dienstag, den 10.03.2020, 22:15 +0100 schrieb Jacek Anaszewski:
> Hi Denis,
> 
> Thank you for the update. Please find my remarks below.
> 
> On 3/10/20 4:19 PM, Denis Osterland-Heim wrote:
> > Hi,
> > 
...
> > > --- a/drivers/leds/leds-pwm.c
> > > +++ b/drivers/leds/leds-pwm.c
> > > @@ -75,7 +75,8 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
> > >  	led_data->active_low = led->active_low;
> > >  	led_data->cdev.name = led->name;
> > >  	led_data->cdev.default_trigger = led->default_trigger;
> > > -	led_data->cdev.brightness = LED_OFF;
> > > +	ret = led->default_state == LEDS_GPIO_DEFSTATE_ON;
> 
> ret is for return value and it should not be used for anything
> else just because it is at hand. Also LEDS_GPIO* definitions have
> nothing to do with pwm leds. This is legacy because default-state
> property was primarily specific to leds-gpio bindings and only
> later was made common.
> 
> Please introduce corresponding LEDS_PWM definitions, but in leds-pwm.c.
will change

> 
> > > +	led_data->cdev.brightness = ret ? led->max_brightness : LED_OFF;
> 
> Instead of above two changes I'd add below:
> 
> if (led->default_state == LEDS_PWM_DEFSTATE_ON) {
> 	led_data->cdev.brightness = led->max_brightness;
> } else if (led->default_state == LEDS_PWM_DEFSTATE_KEEP)) {
> 	// here put what you're adding below, but please use
> 	// pwm_get_state() instead of accessing ops directly
> }
> 
> LED_OFF case is covered by kzalloc() in led_pwm_probe().
Looks very elegant, I will apply this.
pwm_get_state() is not sufficient here because it only returns the values from structure,
which were not read read from registers at pwm_device_request().
Something like pwm_get_state_uncached() would be required, which I have not found yet.

I looked at the atomic PWM API (5ec803edcb703fe379836f13560b79dfac79b01d),
which claims to provide a smooth handover from bootloader to kernel.
So it seems it would be better to fix the FIXME first, in a first patch.

Regards Denis

> 
> > >  	led_data->cdev.max_brightness = led->max_brightness;
> > >  	led_data->cdev.flags = LED_CORE_SUSPENDRESUME;
> > >  
...



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