Re: [PATCH V4 2/2] pwm: Add GPIO PWM driver

[Sean Young <sean@xxxxxxxx>]

On Thu, Feb 29, 2024 at 08:45:54AM +0000, Sean Young wrote:
> On Tue, Feb 27, 2024 at 05:59:40PM +0100, Stefan Wahren wrote:
> > Hi Chris,
> > 
> > Am 27.02.24 um 16:32 schrieb Chris Morgan:
> > > I have a series of devices with GPIO controlled force feedback that
> > > this driver helps us control better. So I'm looking forward to this,
> > > thank you.
> > Thanks for testing. I didn't had much time recently and i was fighting
> > with hr timer resolution stuff. But will try to send the next version in
> > March.
> > > Note that when I set the resolution too low (I got confused and set
> > > the period to 255) my device locked up hard and only a forced
> > > power cycle could bring it back.
> > Unfortunately this is a general design issue by driving the GPIO by a
> > kernel driver and "expected" behavior. I didn't have a good solution for
> > it yet.
> 
> When we reprogram the timer with hrtimer_forward(), we could check whether
> we have overrun - i.e. we are already beyond the expires time. This could
> be a hint that a) we cannot generate the pwm signal and b) this might
> be what causes the hang, because we are returning HRTIMER_RESTART yet
> no new expires has been programmed.

I mean something like:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/rc/pwm-ir-tx.c#n144


Sean