Re: [PATCH v8 1/2] PWM: atmel-pwm: add PWM controller driver

[Bo Shen]

Hi Thierry,

On 12/04/2013 06:03 PM, Thierry Reding wrote:
> On Wed, Dec 04, 2013 at 10:59:46AM +0800, Bo Shen wrote:
> > Hi Thierry,
> >
> > On 12/03/2013 05:43 PM, Thierry Reding wrote:
> > > On Tue, Dec 03, 2013 at 11:09:12AM +0800, Bo Shen wrote:
> > > > On 12/02/2013 06:59 PM, Thierry Reding wrote:
> > > > > On Mon, Nov 18, 2013 at 05:13:21PM +0800, Bo Shen wrote:
> > > [...]
> > > > > > diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> > > [...]
> > > > > > +	/* Calculate the period cycles */
> > > > > > +	while (div > PWM_MAX_PRD) {
> > > > > > +		div = clk_rate / (1 << pres);
> > > > > > +		div = div * period_ns;
> > > > > > +		/* 1/Hz = 100000000 ns */
> > > > >
> > > > > I don't think that comment is needed.
> > > >
> > > > This is asked to be added.
> > > > And, I think keep it and it won't hurt, what do you think?
> > >
> > > I think it's obvious that you're converting from nanoseconds because of
> > > the _ns prefix in period_ns. But if somebody requested this and everyone
> > > else thinks it's useful, I'm okay with keeping it.
> > >
> > > > > > +	if (test_bit(PWMF_ENABLED, &pwm->flags)) {
> > > > > > +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CDTYUPD, dty);
> > > > > > +	} else {
> > > > > > +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CDTY, dty);
> > > > > > +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CPRD, prd);
> > > > > > +	}
> > > > > > +}
> > > > >
> > > > > Neither version 1 nor version 2 seem to be able to change the period
> > > > > while the channel is enabled. Perhaps that should be checked for in
> > > > > atmel_pwm_config() and an error (-EBUSY) returned?
> > > >
> > > > The period is configured in dt in device tree, or platform data in non
> > > > device tree. Nowhere will update period. So, not code to update period.
> > > > Am I right? If not, please figure out.
> > >
> > > The .config() operation allows the period to be specified. Just because
> > > nobody currently changes it at runtime doesn't mean it can't be done.
> > >
> > > It is also possible that whoever wrote the device tree or platform data
> > > didn't know that the period must be the same for all PWM channels and
> > > therefore might use different values. If you check for this, at least
> > > they'll notice. If you don't check for it, then they may end up having
> > > the period reconfigured behind their backs, which may cause parts of
> > > their setup to behave unexpectedly.
> >
> > Thanks for this information.
> > I will add code for changing period.
>
> Just to clarify: I wouldn't want this code to allow changing the period
> but rather reject incompatible changes to the period with an error code.

So, in this patch, just check it as you suggested in previous email, 
would it be OK?
--->8---
Perhaps that should be checked for in atmel_pwm_config() and an error 
(-EBUSY) returned?
---8<---

> Thierry

Best Regards,
Bo Shen

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