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

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Date:   Tue, 25 Apr 2017 19:28:06 +0200
From:   Marek Vasut <marex@...x.de>
To:     Leonard Crestez <leonard.crestez@....com>,
        Fabio Estevam <festevam@...il.com>
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 04/25/2017 07:23 PM, Leonard Crestez wrote:
> 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.

Hehehe :-)

> 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).

Oh that's nice , thanks ! I don't have SDB and I hacked it up after a
brief discussion with Fabio without even compile-testing it, thus RFC.
Glad to hear it works and thanks for testing it ! Can you add a formal
Tested-by please ?

-- 
Best regards,
Marek Vasut