From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Greg KH <greg@kroah.com>
Subject: Re: [PATCH 0/4] Fix runtime device suspend/resumre interface
Date: Wed, 1 Mar 2006 12:31:45 +0100
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Cc: Patrick Mochel <mochel@digitalimplant.org>, akpm@osdl.org,
       torvalds@osdl.org, linux-kernel@vger.kernel.org, linux-pm@osdl.org
References: <Pine.LNX.4.50.0602201641380.21145-100000@monsoon.he.net> <Pine.LNX.4.50.0602271111101.28882-100000@monsoon.he.net> <20060301003810.GI23716@kroah.com>
In-Reply-To: <20060301003810.GI23716@kroah.com>
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On Wednesday 01 March 2006 01:38, Greg KH wrote:
> On Mon, Feb 27, 2006 at 11:18:43AM -0800, Patrick Mochel wrote:
> > 
> > On Tue, 21 Feb 2006, Greg KH wrote:
> > 
> > > On Mon, Feb 20, 2006 at 04:55:34PM -0800, Patrick Mochel wrote:
> > > >
> > > > Hi there,
> > > >
> > > > Here is an updated version of the patches to fix the sysfs interface for
> > > > runtime device power management by restoring the file to its originally
> > > > designed behavior - to place devices in the power state specified by the
> > > > user process writing to the file.
> > > >
> > > > Recently, the interface was changed to filter out values to prevent a
> > > > BUG() that was introduced in the PCI power management code. While a valid
> > > > fix, it makes the driver core filter values that might otherwise be used
> > > > by the bus/device drivers.
> > >
> > > Are there any existing bus/device drivers that are currently broken
> > > because of this change?
> > 
> > It's difficult to tell. There are several devices that support multiple
> > PCI power states, and several drivers that will attempt to put the device
> > into whatever state is passed to their ->suspend() method. But, there are
> > not many that handle D1 or D2 specially.
> > 
> > The point of the patches was to restore the functionality of the sysfs
> > file to its documented interface, which had been that way since the file
> > was created (early in 2.6). In the last year, since the conversion to the
> > pm_message_t in driver suspend methods, it is not behaved as it was
> > advertised to do.
> > 
> > One solution is to prohibit any suspend/resume commands besides "on" and
> > "off", and to change the documented semantics of the file. But, it seems
> > much more useful to enable the use of the intermediate states, so long as
> > it doesn't do any serious harm. Put another way, it doesn't seem to make
> > sense to intentionally prevent the use of intermediate power states.
> > 
> > What is also a bit wonky is the handling of those intermediate power
> > states now. If someone has a PCI device that advertises D1/D2 support, and
> > he/she knows the driver supports it (or is writing the driver support for
> > it), a write of "1" or "2" to the device's state file is not going to
> > provide the type of behavior that one would expect..
> > 
> > Does that help at all?
> 
> Hm, no.  As nothing can be proven to be broken right now, it's way too
> late to get any change like this into 2.6.16-final.  Especially as your
> patch series broke Andrew's laptop :)

And mine too, FWIW. ;-)

Greetings,
Rafael
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