linux-kernel - Re: [RFC][PATCH 0/3] PM: Mechanism to avoid resuming runtime-suspended devices during system suspend

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Date:	Mon, 17 Feb 2014 00:49:33 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Aaron Lu <aaron.lu@...el.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/3] PM: Mechanism to avoid resuming runtime-suspended devices during system suspend

On Wednesday, January 15, 2014 12:12:29 AM Rafael J. Wysocki wrote:
> Hi,
> 
> The following experimental series of 3 patches implements a mechanism allowing
> subsystems to avoid resuming runtime-suspended devices during system suspend.
> 
> As far as the PM core goes, it introduces a new flag, power.no_suspend, that
> will be set by the core for devices which can stay suspended.  The idea is that
> subsystems should know which devices can stay suspended over system suspend
> and to allow them to tell the core about that patch [1/3] changes the calling
> convention of the device PM .prepare() callback so that it can return a positive
> value on success to be interpreted as "this device has been runtime-suspended
> and doesn't need to be resumed" information.  If .prepare() returns a positive
> number for certain device, the core will set power.no_suspend and will not run
> suspend callbacks for device with that flag set going forward (during this
> particular system suspend transition).
> 
> However, parents may generally need to be resumed so that the suspend of their
> children can be carried out, so the PM core will clear power.no_suspend for
> the parents of devices whose power.no_suspend is not set (unless those parents
> have power.ignore_children set).
> 
> Patch [2/3] adds a new runtime PM helper function that subsystems can use to
> check whether or not a given device is runtime-suspended when .prepare() is being
> executed for it.
> 
> Patch [3/3] implements the subsystem part for the ACPI PM domain, because that
> is relatively straightforward.  If the general approach makes sense, I'll think
> about doing the same for PCI.

I have a new version of this.

The new patch [1/3] goes farther than the previous one, because I realized that
all subsystems returning values greater from zero from their .prepare()
callbacks will want to skip .resume_noirq() and .resume_early() for the
"fast suspended" devices and all of them will likely want to run a
pm_request_resume() for those devices in their .resume().  So, if all of
them would do that anyway, it's better if the core does that for them.
Of course, that simplifies patch [3/3] quite a bit.  Patch [2/3] is the
same as before.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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