linux-kernel - Re: [PATCH] Fix /sys/device/.../power/state regression

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Message-ID: <20070127012623.GB13534@srcf.ucam.org>
Date:	Sat, 27 Jan 2007 01:26:23 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Greg KH <gregkh@...e.de>
Cc:	Andrew Morton <akpm@...l.org>,
	David Brownell <david-b@...bell.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix /sys/device/.../power/state regression

On Fri, Jan 26, 2007 at 12:42:26PM -0800, Greg KH wrote:

> No, it's not stable material, as drivers would have to be modified to
> support it, and that is adding new stuff.  See my other comment about
> why this was changed because it was broken...

Which drivers? The current code simply bails if the bus (not the device) 
supports the late_suspend method. In the PCI core, that function simply 
calls the device's late_suspend method and does nothing else. My patch 
simply alters the check so that the bus can veto the request if the 
driver has such a method, and allow it to pass if it doesn't. To 
summarise:

2.6.18 situation:

/sys/devices/.../power/state call will succeed for all PCI devices, even 
if the device suspend method must be called with interrupts disabled

2.6.19 situation:

/sys/devices/.../power/state call will fail for all PCI devices, even if 
the PCI bus's suspend_late function is effectively a noop for that 
device

2.6.19+my patch situation:

/sys/devices/.../power/state call will fail for PCI devices that 
implement a suspend_late method, and succeed for other PCI devices

Surely the latter of these is the closest to the expected behaviour?
-- 
Matthew Garrett | mjg59@...f.ucam.org
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