[PATCH 0/2] pwm: brcmstb: Some cleanups

[Uwe Kleine-König]

On Mon, Feb 14, 2022 at 09:18:49AM -0800, Florian Fainelli wrote:
> On 2/14/22 12:23 AM, Uwe Kleine-König wrote:
> > Hello,
> > 
> > here are a few cleanups for the brcmstb PWM driver. There are a few
> > issues left with it, that I'm not addressing for now. Just mention it in
> > case someone wants to work on this driver:
> > 
> >  - There is no .get_state() callback
> >    (That needs to be implemented by some with hardware and
> >    documentation)

Assuming you have access to documentation, can you confirm, that the
registers that define the PWM's behaviour are readable? If I knew that I
could come up with an implementation for .get_state().

> >  - There are a few places where an overflow can happen in
> >    brcmstb_pwm_config() that are not handled
> > 
> >  - The loop in brcmstb_pwm_config() to calculate cword is ineffective,
> >    cword could be calculated ad hoc.
> > 
> >  - I don't understand
> > 
> >                 /*
> >                  * We can be called with separate duty and period updates,
> >                  * so do not reject dc == 0 right away
> >                  */
> >                 if (pc == PWM_PERIOD_MIN || (dc < PWM_ON_MIN && duty_ns))
> >                         return -EINVAL;
> > 
> >    The usual policy is "With the selected period, pick the biggest
> >    possible duty_cycle that isn't bigger thatn the requested duty_cycle.
> >    So should this case be handled using dc = 0 instead?
> >    But as I don't understand the real issue here (is this about changing
> >    period and duty at the same time?), I don't want to touch that.
> 
> IIRC, I was testing using a shell script that would exercise corner
> cases by modifying the /sys/class/pwm/*/{period,duty_cycle} separately
> was able to run into that. Let me see if I can dig up that script.

When you find it, it would be great to document the problem in a way
that it's still understandable some time later.

> Can you give me a day or two to make sure your changes work properly? I
> need to locate a board with an exposed PWM header so I can put a scope
> on it. Thanks!

Sure, in my experience it takes longer than two days on average until
Thierry picks up PWM patches. Thanks for your willingness to test!

Best regards
Uwe

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