Hi Thierry, Uwe,
> From: Uwe Kleine-Konig, Sent: Friday, December 7, 2018 6:14 PM
>
> On Fri, Dec 07, 2018 at 05:29:33PM +0900, Yoshihiro Shimoda wrote:
> > This PWM Timer cannot output low because setting 0x000 is prohibited
> > on PWMCNT.PH0 (High-Level Period) bitfields. So, avoiding
> > the prohibited, this patch adds a workaround function to change
> > the value from 0 to 1 as pseudo low level.
> >
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> > ---
> > drivers/pwm/pwm-rcar.c | 15 +++++++++++++++
> > 1 file changed, 15 insertions(+)
> >
> > diff --git a/drivers/pwm/pwm-rcar.c b/drivers/pwm/pwm-rcar.c
> > index e479b6a..888cb37 100644
> > --- a/drivers/pwm/pwm-rcar.c
> > +++ b/drivers/pwm/pwm-rcar.c
> > @@ -166,6 +166,20 @@ static void rcar_pwm_disable(struct rcar_pwm_chip *rp)
> > rcar_pwm_update(rp, RCAR_PWMCR_EN0, 0, RCAR_PWMCR);
> > }
> >
> > +static void rcar_pwm_workaround_output_low(struct rcar_pwm_chip *rp)
> > +{
> > + /*
> > + * This PWM Timer cannot output low because setting 0x000 is
> > + * prohibited on PWMCNT.PH0 (High-Level Period) bitfields. So, avoiding
> > + * the prohibited, this function changes the value from 0 to 1 as
> > + * pseudo low level.
> > + *
> > + * TODO: Add GPIO handling to output low level.
> > + */
> > + if ((rp->pwmcnt & RCAR_PWMCNT_PH0_MASK) == 0)
> > + rp->pwmcnt |= 1;
>
> In my eyes this is too broken to do. Not sure I have the complete
> picture, but given a small period (say 2) this 1 cycle might result in
> 50 % duty cycle. Depending on how the hardware behaves if you disable
> it, better do this instead.
My colleague suggests that this workaround code also changes the period
as maximum (1023) to avoid 50 % duty cycle for such a case.
What do you think that this idea is acceptable for upstream? Or, should
I add gpio handling that Uwe suggested?
Best regards,
Yoshihiro Shimoda
> Are you aware of the series adding such gpio support to the imx driver?
>
> @Thierry: So there are three drivers now that could benefit for a
> generic approach.
