linux-kernel - Re: [PATCH v3] soc: imx: gpc: Turn PU domain on/off in sleep on 6qp

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Message-ID: <CAPDyKFrd=jvYfCgtUD6ocEYLHhm1r73SpKB-c7syT3FmwWtaHw@mail.gmail.com>
Date:   Tue, 10 Jul 2018 11:34:09 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Leonard Crestez <leonard.crestez@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Fabio Estevam <fabio.estevam@....com>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        Robin Gong <yibin.gong@....com>,
        Dong Aisheng <aisheng.dong@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH v3] soc: imx: gpc: Turn PU domain on/off in sleep on 6qp

On 10 July 2018 at 10:05, Lucas Stach <l.stach@...gutronix.de> wrote:
> Am Dienstag, den 10.07.2018, 00:27 +0200 schrieb Ulf Hansson:
>> > On 6 July 2018 at 18:46, Leonard Crestez <leonard.crestez@....com> wrote:
>> > On imx6qp power gating on the PU domain is disabled because of errata
>> > ERR009619. However power gating during suspend/resume can still be
>> > performed.
>>
>> Sounds a bit hand wavy. Exactly why can it be done during system suspend/resume?
>
> Power gating this domain in normal operation may introduce a glitch in
> unrelated modules, potentially disturbing a running display scanout.
> This is not a concern when the whole system enters suspend state, so
> it's safe to do in this case.

Makes sense. Could we please fold this information into the commit
message to make this clear!?

>
> Regards,
> Lucas
>
>> >
>> > Enable this by implementing SLEEP_PM_OPS in imx_pgc_power_domain_driver.
>> >
>> > In order to ensure correct ordering add device links from devices inside
>> > the PU domain to the pgc platform_device.
>>
>> In genpd, the PM domain gets powered off after all device's
>> corresponding ->suspend_noirq() callback has been invoked - and it
>> also considers if there are some wakeup settings enabled, possibly
>> avoiding to do the power off.
>>
>> It sound like the imx's power domain driver ->power_off|on() callback
>> should deal with this, to make get a consistent behavior. I understand
>> that you currently can't tell under what circumstances the
>> ->power_off|on() callbacks are being invoked, that may need some
>> changes in genpd.
>>
>> Currently we have a flag, GENPD_FLAG_ALWAYS_ON which makes genpd to
>> always prevent power off. Perhaps we should add a new flag
>> "GENPD_FLAG_RUNTIME_ON", which makes genpd to call the
>> ->power_on|off() callbacks, but only during system wide PM.
>>
>> Thoughts?
>
> Yes, this might work for this case.

Alright. I can help to implement, if you want. Just tell.

Kind regards
Uffe