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Date: Thu, 15 Feb 2024 11:12:30 +0100
From: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To: Viorel Suman <viorel.suman@nxp.com>
Cc: "Viorel Suman (OSS)" <viorel.suman@oss.nxp.com>, 
	Florin Leotescu <florin.leotescu@nxp.com>, Shawn Guo <shawnguo@kernel.org>, 
	Sascha Hauer <s.hauer@pengutronix.de>, Pengutronix Kernel Team <kernel@pengutronix.de>, 
	Fabio Estevam <festevam@gmail.com>, NXP Linux Team <linux-imx@nxp.com>, linux-pwm@vger.kernel.org, 
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] pwm: imx-tpm: reset module on probe
Message-ID: <zeieriiouilwf23g4v5wv7oetdee43qcm5lvxiygyxmxm7lgde@m3a2uain6g45>
References: <20240201122242.1597601-1-viorel.suman@oss.nxp.com>
 <vvldfzpthexjb7bir5imrdslgnnqztl2rdclfp6qiesj6hgiea@o53kcxs66mjr>
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Hello,

On Thu, Feb 01, 2024 at 06:25:26PM +0200, Viorel Suman wrote:
> On 2/1/24 15:38, Uwe Kleine-K=F6nig wrote:
> > > +	/* Resets all internal logic and registers */
> > > +	writel(PWM_IMX_TPM_GLOBAL_RST, tpm->base + PWM_IMX_TPM_GLOBAL);
> > > +	writel(0, tpm->base + PWM_IMX_TPM_GLOBAL);
> > > +
> > This opposes the use case that the bootloader setup the pwm-backlight to
> > show a splash screen that is simply taken over by Linux without
> > flickering, right?
>=20
> Yes, I was not aware of such use case. Is it acceptable if I'll update
>=20
> the patch in a such way so that the software reset happens as function
>=20
> of a property in the related DTS node ?

That sounds wrong. Why do you reset at all? If at all, only reset if all
channels are disabled (if at all).

> > Otherwise the commit log should motivate why "the module takes the
> > default state" is better than the status quo and what this default state
> > is.
>=20
> The default state above means IP internal logic being reset to the initial
> state and
>=20
> registers values being set to their reset values. We're facing a situation
> on iMX95 when
>=20
> A core may be reset independently from the rest of the SoC, this triggers=
 a
> new
>=20
> SPL->U-Boot->Linux boot, and in Linux probe phase PWM will inherit its st=
ate
> from
>=20
> previous Linux runtime - this leads to some issues in suspend/resume
> functionality.

What kind of issues?

Best regards
Uwe

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

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