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.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
