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

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Message-ID: <ZpFAd+Mp2JFnaPet@lizhi-Precision-Tower-5810>
Date: Fri, 12 Jul 2024 10:40:55 -0400
From: Frank Li <Frank.li@....com>
To: Stefan Wahren <wahrenst@....net>
Cc: Uwe Kleine-König <ukleinek@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>, linux-pwm@...r.kernel.org,
	devicetree@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Clark Wang <xiaoning.wang@....com>, Jun Li <jun.li@....com>,
	pratikmanvar09@...il.com
Subject: Re: [PATCH 3/3] pwm: imx27: workaround of the pwm output bug when
 decrease the duty cycle

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@....com>
> > 
> > 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@....com>
> > Signed-off-by: Clark Wang <xiaoning.wang@....com>
> > Signed-off-by: Frank Li <Frank.Li@....com>
> 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@nxp.com/
> [2] -
> https://lore.kernel.org/linux-pwm/20231229063013.1786-1-pratikmanvar09@gmail.com/