Re: [PATCH 3/3] pwm: imx27: workaround of the pwm output bug when decrease the duty cycle

[Frank Li]

On Fri, Jul 12, 2024 at 08:26:17AM +0200, Stefan Wahren wrote:
> Hi Frank,
> 
> Am 11.07.24 um 23:08 schrieb Frank Li:
> > From: Clark Wang <xiaoning.wang@xxxxxxx>
> > 
> > When the SAR FIFO is empty, the write value is directly applied to SAR even
> > though the current period is not over. If the new SAR value is less than
> > the old one and the counter is greater than the new SAR value, the current
> > period will not flip the level. This result in a pulse with a 100% duty
> > cycle.
> > 
> > Write the old SAR value before updating the new duty cycle to SAR. This
> > avoids writing the new value into an empty FIFO.
> > 
> > This only resolves the issue when the PWM period is longer than 2us
> > (or <500KHz) because write register is not quick enough when PWM period is
> > very short.
> > 
> > Reviewed-by: Jun Li <jun.li@xxxxxxx>
> > Signed-off-by: Clark Wang <xiaoning.wang@xxxxxxx>
> > Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> the same patch has been submitted from other people in the past and they
> received many review comments [1], [2].
> 
> Can you please explain which version of the patch this is and does it
> address any review comments?

Thank, I am not realize someone already submitted before. I fixed some by
common senses. Let me double check to make sure to fix all. 

Frank

> 
> Best regards
> 
> [1] -
> https://lore.kernel.org/linux-pwm/20211220073130.1429723-1-xiaoning.wang@xxxxxxx/
> [2] -
> https://lore.kernel.org/linux-pwm/20231229063013.1786-1-pratikmanvar09@xxxxxxxxx/