Re: [PATCH v3 3/5] pwm-backlight: add support for PWM delays proprieties.

[Daniel Thompson]

On 20/07/17 09:06, Pavel Machek wrote:
> Hi!
>
> > > --- a/drivers/video/backlight/pwm_bl.c
> > > +++ b/drivers/video/backlight/pwm_bl.c
> > > @@ -10,6 +10,7 @@
> > >    * published by the Free Software Foundation.
> > >    */
> > > +#include <linux/delay.h>
> > >   #include <linux/gpio/consumer.h>
> > >   #include <linux/gpio.h>
> > >   #include <linux/module.h>
> > > @@ -35,6 +36,7 @@ struct pwm_bl_data {
> > >   	struct gpio_desc	*enable_gpio;
> > >   	unsigned int		scale;
> > >   	bool			legacy;
> > > +	unsigned int		pwm_delay[2];
> >
> > Two named members would be better here (eliminating the "magic" 0
> > and 1).
>
> My thought, too.
>
> > > @@ -56,6 +58,9 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)
> > >   	pwm_enable(pb->pwm);
> > > +	if (pb->pwm_delay[0])
> > > +		usleep_range(pb->pwm_delay[0], pb->pwm_delay[0] * 2);
>
> Plus I'd just do the delay unconditionally :-).

... does this still apply if this code is switched to msleep()?

msleep() has no wait avoidance[1] and if lots of drivers are reckless 
about sleeping for 10ms it soon starts to show up in the boot time 
(especially optimized ones).


Daniel.


[1] As it happens I can't see that many early bail out paths in
    usleep_range() either.