linux-kernel - Re: [PATCH] pwm: imx27: workaround of the pwm output bug

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Message-ID: <sdqgerar4utskfvp2pxbjsjesf2s5zuxtlssur2v3kdvq5m7a6@jaueiad7zvcf>
Date: Wed, 3 Jan 2024 13:18:14 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Francesco Dolcini <francesco@...cini.it>
Cc: pratikmanvar09@...il.com, linux-pwm@...r.kernel.org, 
	shawnguo@...nel.org, s.hauer@...gutronix.de, Pratik Manvar <pratik.manvar@....com>, 
	linux-kernel@...r.kernel.org, thierry.reding@...il.com, Clark Wang <xiaoning.wang@....com>, 
	linux-imx@....com, kernel@...gutronix.de, festevam@...il.com, 
	linux-arm-kernel@...ts.infradead.org, Jun Li <jun.li@....com>
Subject: Re: [PATCH] pwm: imx27: workaround of the pwm output bug

On Wed, Jan 03, 2024 at 11:34:21AM +0100, Francesco Dolcini wrote:
> On Fri, Dec 29, 2023 at 12:00:07PM +0530, pratikmanvar09@...il.com wrote:
> > From: Clark Wang <xiaoning.wang@....com>
> > 
> > This fixes the pwm output bug when decrease the duty cycle.
> > This is a limited workaround for the PWM IP issue TKT0577206.
> > 
> > Root cause:
> > When the SAR FIFO is empty, the new write value will be directly applied
> > to SAR even 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 filp the
> > level. This will result in a pulse with a duty cycle of 100%.
> > 
> > Workaround:
> > Add an old value SAR write before updating the new duty cycle to SAR.
> > This will keep the new value is always in a not empty fifo, and can be
> > wait to update after a period finished.
> > 
> > Limitation:
> > This workaround can only solve this issue when the PWM period is longer
> > than 2us(or <500KHz).
> > 
> > Reviewed-by: Jun Li <jun.li@....com>
> > Signed-off-by: Clark Wang <xiaoning.wang@....com>
> > Link: https://github.com/nxp-imx/linux-imx/commit/16181cc4eee61d87cbaba0e5a479990507816317
> > Tested-by: Pratik Manvar <pratik.manvar@....com>
> 
> You need to add your signed-off-by at the end when sending a patch, no
> matter if you are the author or not.

FTR: This also applies to the v2 patch. I discarded both from the pwm
patchwork.

Best regards
Uwe

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

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