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

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Message-ID: <3EDFF987-82C2-4B0A-9488-037D1BD4CA48@walle.cc>
Date:   Fri, 17 Sep 2021 10:21:25 +0200
From:   Michael Walle <michael@...le.cc>
To:     Heiko Thiery <heiko.thiery@...il.com>,
        Frieder Schrempf <frieder.schrempf@...tron.de>
CC:     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

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? 

-michael