Re: [linux-sunxi] [RFC PATCH 4/4] pwm: sun4i: Delay after writing the period

[Pascal Roeleven]

On 2020-04-22 05:43, Samuel Holland wrote:
> Hello Pascal,
>
> On 3/17/20 10:59 AM, Pascal Roeleven wrote:
> > When disabling, ensure the period write is complete before continuing.
> > This fixes an issue on some devices when the write isn't complete 
> > before
> > the panel is turned off but the clock gate is still on.
> >
> > Signed-off-by: Pascal Roeleven <dev@xxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/pwm/pwm-sun4i.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> > index a11d00f96..75250fd4c 100644
> > --- a/drivers/pwm/pwm-sun4i.c
> > +++ b/drivers/pwm/pwm-sun4i.c
> > @@ -299,6 +299,10 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, 
> > struct pwm_device *pwm,
> >  	sun4i_pwm_writel(sun4i_pwm, val, PWM_CH_PRD(pwm->hwpwm));
> >  	next_period = jiffies + usecs_to_jiffies(cstate.period / 1000 + 1);
> >
> > +	/* When disabling, make sure the period register is written first */
> > +	if (!state->enabled && cstate.enabled)
> > +		sun4i_pwm_wait(next_period);
> > +
>
> It is not visible from the context of this patch, but this call to
> sun4i_pwm_wait() ends up calling msleep() inside a spinlock, which 
> isn't
> allowed. The spinlock should probably be converted to a mutex, 
> considering that
> sun4i_pwm_apply() already sleeps and takes mutexes.
>
> Regards,
> Samuel

Yes you're right. A different implementation of this patch series is 
being worked on, in which I'll take this into account. Unfortunately I 
have other things to work on at the moment, so it might take a while.

Regards,
Pascal