linux-kernel - Re: [RFC PATCH 2/6] ACPI: Reference devices in ACPI Power Resource

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Date:	Tue, 21 Feb 2012 11:06:39 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lin Ming <ming.m.lin@...el.com>
cc:	"Zhang, Rui" <rui.zhang@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Jeff Garzik <jgarzik@...ox.com>,
	Tejun Heo <tj@...nel.org>, Len Brown <lenb@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH 2/6] ACPI: Reference devices in ACPI Power Resource

On Tue, 21 Feb 2012, Lin Ming wrote:

> > Then maybe you can use pm_runtime_no_callbacks() for the ZPODD device.
> > It's explained in Documentation/power/runtime_pm.txt, and I use it for
> > USB interfaces.
> 
> If pm_runtime_no_callbacks() is used, runtime PM sysfs attributes
> won't be created.
> Then how to disable ZPODD feature in userspace?
> 
> Currently, I use "control" file of scsi device to enable/disable
> ZPODD, for example
> echo auto > /sys/devices/pci0000:00/0000:00:1f.2/ata0/host1/target1:0:0/1:0:0:0/power/control
> echo on > /sys/devices/pci0000:00/0000:00:1f.2/ata0/host1/target1:0:0/1:0:0:0/power/control

You could get the same result by using the "control" file for the ATA
port.

> > The idea is that the ZPODD will never receive any runtime PM callbacks
> > from the PM core.  Instead the ATA port callback routines will be
> > responsible for power management of the ZPODD device.
> 
> Does the ATA port callback also responsible to resume its child?
> 
> For example,
> /sys/devices/pci0000:00/0000:00:1f.2/ata0/host1/target1:0:0/1:0:0:0/
> 
> ata0 is resumed.
> 
> Then who will be responsible to resume host1, target1:0:0 and 1:0:0:0?
> 
> Or do you mean that we don't need to resume these devices at all?
> host1 and target1:0:0 are logical devices, but I think 1:0:0:0 is not.

That's right.  It makes no difference whether the host and target 
are resumed or suspended.  In fact, you could also call 
pm_runtime_no_callbacks() for them.

Alan Stern

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