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Date: Wed, 3 Jan 2024 13:18:14 +0100
From: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To: Francesco Dolcini <francesco@dolcini.it>
Cc: pratikmanvar09@gmail.com, linux-pwm@vger.kernel.org, 
	shawnguo@kernel.org, s.hauer@pengutronix.de, Pratik Manvar <pratik.manvar@ifm.com>, 
	linux-kernel@vger.kernel.org, thierry.reding@gmail.com, Clark Wang <xiaoning.wang@nxp.com>, 
	linux-imx@nxp.com, kernel@pengutronix.de, festevam@gmail.com, 
	linux-arm-kernel@lists.infradead.org, Jun Li <jun.li@nxp.com>
Subject: Re: [PATCH] pwm: imx27: workaround of the pwm output bug
Message-ID: <sdqgerar4utskfvp2pxbjsjesf2s5zuxtlssur2v3kdvq5m7a6@jaueiad7zvcf>
References: <20231229063013.1786-1-pratikmanvar09@gmail.com>
 <20240103103421.GA3758@francesco-nb>
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On Wed, Jan 03, 2024 at 11:34:21AM +0100, Francesco Dolcini wrote:
> On Fri, Dec 29, 2023 at 12:00:07PM +0530, pratikmanvar09@gmail.com wrote:
> > From: Clark Wang <xiaoning.wang@nxp.com>
> >=20
> > This fixes the pwm output bug when decrease the duty cycle.
> > This is a limited workaround for the PWM IP issue TKT0577206.
> >=20
> > 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%.
> >=20
> > 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.
> >=20
> > Limitation:
> > This workaround can only solve this issue when the PWM period is longer
> > than 2us(or <500KHz).
> >=20
> > Reviewed-by: Jun Li <jun.li@nxp.com>
> > Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
> > Link: https://github.com/nxp-imx/linux-imx/commit/16181cc4eee61d87cbaba=
0e5a479990507816317
> > Tested-by: Pratik Manvar <pratik.manvar@ifm.com>
>=20
> 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

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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