Hi Uwe,
> From: Uwe Kleine-Konig, Sent: Monday, December 10, 2018 5:11 PM
>
> Hello,
>
> On Mon, Dec 10, 2018 at 04:49:17AM +0000, Yoshihiro Shimoda wrote:
> > > 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:
> > <snip>
> > > > +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.
> >
> > You're right.
>
> But in the meantime I learned that the pwm gets active on disable, so
> this won't help.
>
> > > Are you aware of the series adding such gpio support to the imx driver?
> >
> > I didn't know that.
> >
> > > @Thierry: So there are three drivers now that could benefit for a
> > > generic approach.
> >
> > Should I wait for Thierry's opinion whether PWM subsystem will have
> > a generic approach or not?
>
> Not sure how to preceed here. The needed procedure would be:
>
> set duty_cycle to 0%
> delay long enough to be sure the duty cycle is active
> switch to gpio
> disable the hardware
>
> The additional blocker for rcar is that it doesn't support duty_cycle
> 0%.
>
> So unless your hardware guys confirm that 0% works even though not
> supported according to the hardware manual I have no good idea.
>
> In the past I suggested to weaken the requirements after pwm_disable,
> but Thierry didn't like it.
I read the following discussion once:
https://patchwork.ozlabs.org/patch/959776/
I could not understand all this yet, but I think I should try to add a special gpio handling
to the pwm-rcar.c driver instead of a generic approach because as you mentioned above,
such special handling needs for the hardware.
Best regards,
Yoshihiro Shimoda
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | http://www.pengutronix.de/ |
