linux-kernel - Re: [PATCH 1/3] ACPI / PM: Only set power states of devices that are power manageable

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Message-ID: <1738639.5UcWLydKxR@vostro.rjw.lan>
Date:	Tue, 30 Jul 2013 16:04:47 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Aaron Lu <aaron.lu@...el.com>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Tejun Heo <tj@...nel.org>,
	linux-ide@...r.kernel.org
Subject: Re: [PATCH 1/3] ACPI / PM: Only set power states of devices that are power manageable

On Tuesday, July 30, 2013 07:43:48 AM Aaron Lu wrote:
> On 07/30/2013 06:21 AM, Rafael J. Wysocki wrote:
> > On Monday, July 29, 2013 10:09:53 PM Aaron Lu wrote:
> >> On 07/27/2013 09:10 PM, Rafael J. Wysocki wrote:
> >>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >>>
> >>> Make acpi_device_set_power() check if the given device is power
> >>> manageable before checking if the given power state is valid for that
> >>> device.  Otherwise it will print that "Device does not support" that
> >>> power state into the kernel log, which may not make sense for some
> >>> power states (D0 and D3cold are supported by all devices by
> >>> definition).
> >>
> >> It will not print "Device does not support" that power state if that
> >> power state is D0 or D3cold since we have unconditionally set those two
> >> power state's valid flag.
> > 
> > So you didn't actually looked at acpi_bus_get_power_flags() that set the
> > power.states[].flags.valid flag, because If you had looked at it, you would
> > have seen that that's not the case.
> > 
> > No, we don't set the valid flag for devices that aren't power manageable
> > (i.e. have flags.power_manageable unset), which is the *whole* *point* of
> > this change.
> 
> Right, I missed this. Sorry for the noise.
> 
> > 
> >> OTOH, what value should we return for a device node that is not power
> >> manageable in acpi_device_set_power when the target state is D0 or D3
> >> cold? The old behavior is to return 0, meanning success without taking
> >> any actual action.
> >>
> >> In acpi_bus_set_power, if the device is not power manageable, we will
> >> return -ENODEV; in acpi_dev_pm_full/low_power, we will return 0 as in
> >> the original acpi_device_set_power. So return -EINVAL here is correct?
> > 
> > No, the original acpi_device_set_power() will return -ENODEV then, but
> > in my opinion returning -EINVAL is more accurate, because "power
> > manageable" means "you can change power state of it".
> 
> Shall I prepare a patch to update the errno in acpi_bus_set_power?

In fact, it doesn't need to check flags.power_manageable after this patch
and the debug message won't be missed I think, so please just remove
the whole if () from there, if that's not a problem.

Thanks,
Rafael


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