linux-kernel - Re: [PATCH 2/2] PCI PM: Read device power state from register after updating it

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Date:	Thu, 11 Jun 2009 11:54:58 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] PCI PM: Read device power state from register after
 updating it

On Tue, 26 May 2009 21:52:29 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Monday 18 May 2009, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > After attempting to change the power state of a PCI device
> > pci_raw_set_power_state() doesn't check if the value it wrote into
> > the device's PCI_PM_CTRL register has been stored in there.  Still,
> > it modifies the device's current_state field as though that's the
> > case.  This may cause the driver of the device to think that its
> > power state has been changed while in fact it hasn't.
> > 
> > To prevent such situations from happening modify
> > pci_raw_set_power_state() so that it reads the device's PCI_PM_CTRL
> > register after writing into it and uses the value read from the
> > register to update the device's current_state field.  Also make it
> > return -EIO if the new state of the device is not equal to the state
> > requested by the called.
> > 
> > To distinguish this error condition from the other ones make
> > pci_raw_set_power_state() return -ENOSYS instead of -EIO when it is
> > impossible to change the power state of the device, because it
> > doesn't support the native PCI PM at all or the requested target
> > state is not supported by it.
> 
> Having reconsidered it I think that -ENODEV is probably better than
> -ENOSYS for this purpose.  Updated patch follows.

Applied to linux-next, thanks Rafael.

-- 
Jesse Barnes, Intel Open Source Technology Center
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