Re: [PATCH v2 5/9] PM / ACPI: Provide option to disable direct_complete for ACPI devices

From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Wolfram Sang <wsa@the-dreams.de>, Len Brown <lenb@kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Kevin Hilman <khilman@kernel.org>,
	Jarkko Nikula <jarkko.nikula@linux.intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jisheng Zhang <jszhang@marvell.com>,
	John Stultz <john.stultz@linaro.org>,
	Guodong Xu <guodong.xu@linaro.org>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	Haojian Zhuang <haojian.zhuang@linaro.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	linux-i2c <linux-i2c@vger.kernel.org>
Subject: Re: [PATCH v2 5/9] PM / ACPI: Provide option to disable direct_complete for ACPI devices
Date: Thu, 24 Aug 2017 02:20:00 +0200	[thread overview]
Message-ID: <9174364.s7oU13Tavs@aspire.rjw.lan> (raw)
In-Reply-To: <3774251.HUIR40xRhc@aspire.rjw.lan>

On Thursday, August 24, 2017 2:13:55 AM CEST Rafael J. Wysocki wrote:
> On Thursday, August 24, 2017 1:39:44 AM CEST Rafael J. Wysocki wrote:
> > On Wed, Aug 23, 2017 at 4:42 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > > In some cases a driver for an ACPI device needs to be able to prevent the
> > > ACPI PM domain from using the direct_complete path during system sleep.
> > >
> > > One typical case is when the driver for the device needs its device to stay
> > > runtime enabled, during the __device_suspend phase. This isn't the case
> > > when the direct_complete path is being executed by the PM core, as it then
> > > disables runtime PM for the device in __device_suspend(). Any following
> > > attempts to runtime resume the device after that point, just fails.
> > 
> > OK, that is a problem.
> > 
> > > A workaround to this problem is to let the driver runtime resume its device
> > > from its ->prepare() callback, as that would prevent the direct_complete
> > > path from being executed. However, that may often be a waste, especially if
> > > it turned out that no one really needed the device.
> > >
> > > For this reason, invent acpi_dev_disable|enable_direct_complete(), to allow
> > > drivers to inform the ACPI PM domain to change its default behaviour during
> > > system sleep, and thus control whether it may use the direct_complete path
> > > or not.
> > 
> > But I'm not sure this is the right place to address it as it very well
> > may affect a PCI device too.
> > 
> > Also, this is about the device and not about its ACPI companion
> > object, so putting the flag in there is somewhat unclean, so to speak.
> > 
> > It looks like we need a flag in dev_pm_info saying something along the
> > lines of "my system suspend callback can deal with runtime PM" that
> > will cause the direct_complete update to occur in
> > __device_suspend_late() instead of __device_suspend().
> 
> IOW, something like the patch below.
> 
> It actually should work with the ACPI PM domain code as is except that it
> will cause the device to be runtime resumed every time during suspend.
> 
> But acpi_subsys_suspend() can be changed to avoid resuming the device if
> power.force_suspend is set.

Or better yet, if power.direct_complete is not set, because that means the
device needs to be resumed anyway.

And if power.direct_complete is set at that point, power.force_suspend has to
be set too.