linux-kernel - Re: [PATCH] fakephp: Allocate PCI resources before adding the device

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Date:	Fri, 28 Nov 2008 11:57:23 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Trent Piepho <xyzzy@...akeasy.org>
Cc:	Alex Chiang <achiang@...com>,
	"Darrick J. Wong" <djwong@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] fakephp: Allocate PCI resources before adding the	device

On Fri, Nov 28, 2008 at 02:11:49AM -0800, Trent Piepho wrote:
> On Wed, 26 Nov 2008, Matthew Wilcox wrote:
> > Because fakephp was the odd one out.  Every other hotplug driver
> > registers a slot number and puts the address in the directory.  We're
> > making hotplug drivers simpler (by sharing more of the logic in the
> > core) and so fakephp had to change to match the other drivers.  I'm
> > sorry for your inconvenience, but it's necessary.
> 
> Seems like changing a long established interface like this should be put on
> the feature removable schedule.

sysfs is more fluid than other interfaces.  Large parts of it
change without warning.  I suppose it could have gone through
feature-removal-schedule, and perhaps we should try to do that in future.

> > We can discuss other ways to make your life better, but it can't be
> > changed back to one 'slot' per PCI function.
> 
> Why not have a slot per pci function with each hotplug driver adding
> attributes to the slot?  The slot would be registered by the hotplug core.

What we have now is the 'address' file managed by the core.  This
doesn't include the function number.

> Is there any reason the fakephp driver should not be allowed to enable and
> disable individual functions?  There a lot of mutli-function devices that
> allow individual functions to be enabled and disabled with registers on the
> primary function.  For instance, it would be possible to work around a BIOS
> that doesn't have an option to disabled a southbridge's USB controller by
> doing so in Linux and then using fakephp to remove the device, and thus
> free address space that other devices might need.

There are lots of circumstances where enabling and disabling individual
functions is a good idea, but I don't think that fakephp is the right
way to do it.  We need a better interface.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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