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

[Phil Howard <phil@gadgetoid.com>]

On Tue, 27 Feb 2024 at 16:59, Stefan Wahren <wahrenst@gmx.net> 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.
>
> What period is too low without limiting other users?
>
> The only idea which comes to my mind is to introduce a kernel parameter
> for this driver to set a lower period limit. This can be provided by
> some administrator or system designer with enough experience. So a
> general user doesn't need to care about it.

This works for me. I also mucked up the period to see what appears to be
a signal in the MHz range, but got a dropped SSH connection for my troubles.

255ns would be ~3.9MHz which is quite spectacularly far outside of the
range I've come to expect from software PWM, but any conservative hard
limit would be trivialised by a faster CPU.

>
> Best regards
>
> > Tested-by: Chris Morgan <macromorgan@hotmail.com>
>

-- 
Philip Howard