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

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Date:	Wed, 31 Jul 2013 12:29:02 +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 Wednesday, July 31, 2013 02:48:58 PM Aaron Lu wrote:
> On 07/30/2013 10:04 PM, Rafael J. Wysocki wrote:
> > 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.
> 
> Patch to remove the redundant check, apply on top of this one.
> 
> From: Aaron Lu <aaron.lu@...el.com>
> Subject: [PATCH 1/3] ACPI / PM: Remove redundant check for power manageable in
>  acpi_bus_set_power
> 
> Now that we will check if a device is power manageable in
> acpi_device_set_power, it is no longer necessary to do this check in
> acpi_bus_set_power, so remove it.
> 
> Signed-off-by: Aaron Lu <aaron.lu@...el.com>

Looks good, I'll queue it up for 3.12.

Thanks,
Rafael


> ---
>  drivers/acpi/device_pm.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
> index 63324b8..8270711 100644
> --- a/drivers/acpi/device_pm.c
> +++ b/drivers/acpi/device_pm.c
> @@ -245,13 +245,6 @@ int acpi_bus_set_power(acpi_handle handle, int state)
>  	if (result)
>  		return result;
>  
> -	if (!device->flags.power_manageable) {
> -		ACPI_DEBUG_PRINT((ACPI_DB_INFO,
> -				"Device [%s] is not power manageable\n",
> -				dev_name(&device->dev)));
> -		return -ENODEV;
> -	}
> -
>  	return acpi_device_set_power(device, state);
>  }
>  EXPORT_SYMBOL(acpi_bus_set_power);
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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