linux-kernel - Re: [PATCH] ARM: dts: imx6sx-sdb: Remove cpufreq OPP override

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Date:   Tue, 25 Apr 2017 20:23:24 +0300
From:   Leonard Crestez <leonard.crestez@....com>
To:     Fabio Estevam <festevam@...il.com>, Marek Vasut <marex@...x.de>
CC:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Peter Chen <Peter.Chen@....com>,
        Anson Huang <Anson.Huang@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Christoph Fritz <chf.fritz@...glemail.com>
Subject: Re: [PATCH] ARM: dts: imx6sx-sdb: Remove cpufreq OPP override

On Tue, 2017-04-25 at 14:02 -0300, Fabio Estevam wrote:
> On Tue, Apr 25, 2017 at 2:02 PM, Fabio Estevam <festevam@...il.com> wrote:
> > 
> > Hi Leonard,
> > 
> > On Tue, Apr 25, 2017 at 1:57 PM, Leonard Crestez
> > <leonard.crestez@....com> wrote:
> > > 
> > > The board file for imx6sx-dbg overrides cpufreq operating points to use
> > > higher voltages. This is done because the board has a shared rail for
> > > VDD_ARM_IN and VDD_SOC_IN and when using LDO bypass the shared voltage
> > > needs to be a value suitable for both ARM and SOC.
> > > 
> > > This was introduced in:
> > > 
> > > commit 54183bd7f766 ("ARM: imx6sx-sdb: add revb board and make it default")
> > > 
> > > This only only applies to LDO bypass mode, a feature not present in
> > > upstream. When LDOs are enabled the effect is to use higher voltages than
> > > necesarry for no good reason.
> > > 
> > > Setting these higher voltages can make some boards fail to boot with ugly
> > > semi-random crashes, reminiscent of memory corruption. These failures
> > > happen the first time the lowest idle state is used. Remove the OPP
> > > override in order to fix those crashes.
> > > 
> > > Signed-off-by: Leonard Crestez <leonard.crestez@....com>
> > > 
> > > ---
> > > It's not clear exactly why the crashes happen. Perhaps waking up from idle
> > > draws more power than is available? Removing this override is a correct
> > > change anyway so maybe there is no need to investigate deeper.

> > Marek just sent a similar one a few minutes ago:
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/503230.html

> Forgot to add Marek.

Wow, that was literally 15 minutes before my patch. In my defense I did
search the archives before starting to format the patch but it had not
arrived yet.

Anyway, that version also sets the supply for reg_arm and reg_soc. It
is not necessary for fixing the crash I'm seeing but is good because it
will result in the minimum voltage on VDD_ARM_SOC_IN rather than a fix
1375mv. I tested Marek's patch and it works fine on my rev B board
(which otherwise fails to boot upstream).

-- 
Regards,
Leonard