Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <9bcf7b749dca57d42aa2e7afd88b5a26f3eeff2a.camel@pengutronix.de>
Subject: Re: [PATCH] arm64: dts: imx8mm-kontron-n801x-som: do not allow to
 switch off buck2
From:   Lucas Stach <l.stach@pengutronix.de>
To:     Heiko Thiery <heiko.thiery@gmail.com>,
        Frieder Schrempf <frieder.schrempf@kontron.de>
Cc:     devicetree@vger.kernel.org,
        Guido =?ISO-8859-1?Q?G=FCnther?= <agx@sigxcpu.org>,
        Fabio Estevam <festevam@gmail.com>,
        Shengjiu Wang <shengjiu.wang@nxp.com>,
        "Angus Ainslie (Purism)" <angus@akkea.ca>,
        linux-kernel@vger.kernel.org,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Joakim Zhang <qiangqing.zhang@nxp.com>,
        Michael Walle <michael@walle.cc>,
        Rob Herring <robh+dt@kernel.org>,
        NXP Linux Team <linux-imx@nxp.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        linux-arm-kernel@lists.infradead.org
Date:   Fri, 17 Sep 2021 13:44:04 +0200
In-Reply-To: <CAEyMn7ZbJr0_2Phc2rW7sDYQu4AABWPZ1F7xDgaS5U7ha7iqzA@mail.gmail.com>
References: <20210915120325.20248-1-heiko.thiery@gmail.com>
         <7e7ee4244ababc0a46e0875222c7e37d@walle.cc>
         <898fd5e0-2073-3689-89b6-2c5071773786@kontron.de>
         <CAEyMn7ZbJr0_2Phc2rW7sDYQu4AABWPZ1F7xDgaS5U7ha7iqzA@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.40.4 (3.40.4-1.fc34) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

Am Freitag, dem 17.09.2021 um 09:28 +0200 schrieb Heiko Thiery:
> Hi Frieder,
> 
> Am Mi., 15. Sept. 2021 um 14:09 Uhr schrieb Frieder Schrempf
> <frieder.schrempf@kontron.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?
> 
> [1] https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/freescale/imx8mq-librem5-devkit.dts#L319
> 
Maybe your kernel config is missing the cpufreq driver, so you don't
have a consumer of the regulator?

Marking the regulator as always-on seems like the right thing to do,
you don't want to depend on a consumer showing up to make sure that
your CPU voltage isn't cut...

Regards,
Lucas