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

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Message-ID: <20090611130052.2b95429c@jbarnes-g45>
Date:	Thu, 11 Jun 2009 13:00:52 -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>,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: [PATCH 2/2] PCI PM: Read device power state from register after
 updating it

On Thu, 11 Jun 2009 12:53:16 -0700
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Thursday 11 June 2009, Jesse Barnes wrote:
> > 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.
> 
> Please drop.  It has been reported by Jiri to cause a regression to
> happen.

Ah as I went through the rebase I thought I remembered something like
that.  Will drop.

Thanks,
-- 
Jesse Barnes, Intel Open Source Technology Center
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