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

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Date:   Tue, 10 Jul 2018 00:27:49 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Leonard Crestez <leonard.crestez@....com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        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 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?

>
> 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?

[...]

Kind regards
Uffe