linux-kernel - Re: [PATCH] arm64: dts: imx8mm-kontron-n801x-som: do not allow to switch off buck2

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Date:   Fri, 17 Sep 2021 10:51:49 +0200
From:   Heiko Thiery <heiko.thiery@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Frieder Schrempf <frieder.schrempf@...tron.de>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Shengjiu Wang <shengjiu.wang@....com>,
        Rob Herring <robh+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>,
        NXP Linux Team <linux-imx@....com>,
        Guido Günther <agx@...xcpu.org>,
        "Angus Ainslie (Purism)" <angus@...ea.ca>
Subject: Re: [PATCH] arm64: dts: imx8mm-kontron-n801x-som: do not allow to
 switch off buck2

HI Michael,

Am Fr., 17. Sept. 2021 um 10:21 Uhr schrieb Michael Walle <michael@...le.cc>:
>
> Am 17. September 2021 09:28:51 MESZ schrieb Heiko Thiery <heiko.thiery@...il.com>:
> >Hi Frieder,
> >
> >Am Mi., 15. Sept. 2021 um 14:09 Uhr schrieb Frieder Schrempf
> ><frieder.schrempf@...tron.de>:
> >>
> >> On 15.09.21 14:05, Michael Walle wrote:
> >> > Am 2021-09-15 14:03, schrieb Heiko Thiery:
> >> >> The buck2 output of the PMIC is the VDD core voltage of the cpu.
> >> >> Switching off this will poweroff the CPU. Add the 'regulator-always-on'
> >> >> property to avoid this.
> >> >
> >> > Mh, have this ever worked? Is there a commit which introduced a regression?
> >>
> >> Yes, this did work before, even without 'regulator-always-on'. I
> >> currently don't understand why this is needed. The regulator is
> >> referenced in the CPU nodes as 'cpu-supply'. This should be enough to
> >> not disable it as long as the CPU is up.
> >
> >I rechecked that with 5.11, 5.10 and 5.9 and I see on all of them the
> >same issue:
> >
> >[ 31.716031] vdd-5v: disabling
> >[ 31.719032] rst-usb-eth2: disabling
> >[ 31.722553] buck2: disabling
> >
> >While on that I tried to compare with other boards and see that they
> >also have the cpu-voltage marked as "regulator-always-on". The only
> >exception in dts/freescale is in imx8mq-librem5-devkit.dts [1] that
> >has not set this property.
> >
> >I agree with you and don't understand why this is happening. Has
> >anyone else an explanation?
>
> Do you have the CPU frequency scaling driver enabled?

That was a good hint. What I now see is in my case the driver is not
loaded (I boot via network). In the default kernel config the module
is marked as 'm'. When switching to 'y' as expected it will be probed
and the the buck2 (cpu-supply) will not be deactivated after 30
seconds.

-- 
Heiko