linux-kernel - Re: [PATCH v2] arm64: dts: imx8mq-kontron-pitx-imx8m: remove vqmmc-supply node

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Message-ID: <CAEyMn7aYYkGZ1Eawd=yazdKeBuHVQc=3F7PnHSCSRyYCu=CJ9A@mail.gmail.com>
Date:   Tue, 14 Sep 2021 11:37:04 +0200
From:   Heiko Thiery <heiko.thiery@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Lucas Stach <l.stach@...gutronix.de>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Fabio Estevam <festevam@...il.com>,
        Shengjiu Wang <shengjiu.wang@....com>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>
Subject: Re: [PATCH v2] arm64: dts: imx8mq-kontron-pitx-imx8m: remove
 vqmmc-supply node

Hi,

Am Di., 14. Sept. 2021 um 11:12 Uhr schrieb Michael Walle <michael@...le.cc>:
>
> Am 2021-09-14 10:52, schrieb Lucas Stach:
> > Am Dienstag, dem 14.09.2021 um 10:32 +0200 schrieb Michael Walle:
> >> Hi Lucas,
> >>
> >> Am 2021-09-14 10:20, schrieb Lucas Stach:
> >> > Am Dienstag, dem 14.09.2021 um 09:26 +0200 schrieb Heiko Thiery:
> >> > > The sw4 output (V_1V8_S0 voltage) from the PMIC is the main supply for
> >> > > the 1V8 power domain. It is not only used as supply for the eMMC.
> >> > > So this voltage can not be changed and is not allowed to switched off.
> >> > > Therefore we do not want to provide this regulator to the SDHC driver
> >> > > to
> >> > > control this voltage.
> >> > >
> >> > This specific requirement should not be solved by removing the
> >> > regulator connection from the SDHCI node, but instead by constraining
> >> > the regulator voltage range to a fixed 3.3V and marking the regulator
> >> > as always-on to reflect the hardware requirements in the DT.
> >> >
> >> > Also if your eMMC vqmmc is a fixed 3.3V, I don't think you need the
> >> > faster pinctrl states, as you can't use the faster pin states anyways,
> >> > as they require a 1.8V signaling voltage.
> >>
> >> Are you speaking of the 1.8V signalling modes? As far as I know the
> >> IMX SDHC controller will switch the voltage by its own function pin.
> >> That is, its not a GPIO.
> >
> > Ah, I mixed things up here. This is a fixed 1.8V supply, which is valid
> > for eMMC, so the high-speed modes are available. My comment still
> > applies that this should be fixed by constraining the regulator, not by
> > removing the DT connection.
> >
> > vqmmc is the MMC IO voltage, which can be switched either by the
> > function pin, which gets toggled automatically when software does the
> > voltage switch, or by explicitly switching the regulator voltage. eMMCs
> > are a bit special as they can work with a fixed 1.8V IO supply and
> > don't need to start with 3.3V.
>
> I tend to agree. There might be some useful information, like the driver
> could fetch the voltage although it is not able to change it.
>
> NB. the regulator is already fixed at 1.8V and is marked as always on.
>
> from arch/arm64/boot/dts/freescale/imx8mq-kontron-pitx-imx8m.dts:
>
> sw4_reg: sw4 {
>          regulator-name = "V_1V8_S0";
>          regulator-min-microvolt = <1800000>;
>          regulator-max-microvolt = <1800000>;
>          regulator-always-on;
> };

To be honest, the intention was that I wanted to separate the
dependency between emmc and PMIC. Debian 11 unfortunately does not
have a driver enabled for the PMIC used and therefore cannot
initialize the emmc driver.

So I should reconsider how to fix this.

-- 
Heiko