linux-kernel - Re: [PATCH v2] arm64: dts: imx8mm-verdin: Link reg_usdhc2

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Message-ID: <20250423102651.GC4811@francesco-nb>
Date: Wed, 23 Apr 2025 12:26:51 +0200
From: Francesco Dolcini <francesco@...cini.it>
To: Frieder Schrempf <frieder.schrempf@...tron.de>
Cc: Francesco Dolcini <francesco@...cini.it>,
	Wojciech Dubowik <Wojciech.Dubowik@...com>,
	linux-kernel@...r.kernel.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>, devicetree@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	Philippe Schenker <philippe.schenker@...ulsing.ch>,
	stable@...r.kernel.org
Subject: Re: [PATCH v2] arm64: dts: imx8mm-verdin: Link reg_usdhc2_vqmmc to
 usdhc2

On Wed, Apr 23, 2025 at 10:00:22AM +0200, Frieder Schrempf wrote:
> Am 23.04.25 um 09:08 schrieb Francesco Dolcini:
> > On Wed, Apr 23, 2025 at 08:50:54AM +0200, Frieder Schrempf wrote:
> >> Am 22.04.25 um 14:46 schrieb Wojciech Dubowik:
> >>>
> >>> Define vqmmc regulator-gpio for usdhc2 with vin-supply
> >>> coming from LDO5.
> >>>
> >>> Without this definition LDO5 will be powered down, disabling
> >>> SD card after bootup. This has been introduced in commit
> >>> f5aab0438ef1 ("regulator: pca9450: Fix enable register for LDO5").
> >>>
> >>> Fixes: f5aab0438ef1 ("regulator: pca9450: Fix enable register for LDO5")
> >>>
> >>> Cc: stable@...r.kernel.org
> >>> Signed-off-by: Wojciech Dubowik <Wojciech.Dubowik@...com>

...

> > With this solution (that I proposed), the sdcard driver just use the
> > GPIO to select the right voltage and that's it, simple, no un-needed i2c
> > communication with the PMIC, and the DT clearly describe the way the HW
> > is designed.
> 
> Yes, but your solution relies on the fact that the LDO5 registers
> actually have the correct values for 1v8 and 3v3 setup. The bootloader
> might have changed these values. I would prefer it if we could have a
> solution that puts the LDO5 in a defined state, that is independent from
> any external conditions.

I do not think this is a real concern, the PMIC is programmed during
manufacturing, if the PMIC programming is not correct we have way more
issues ...

Francesco