linux-kernel - Re: [PATCH WIP 2/5] xen/arm: set xen_platform_pci_unplug to XEN_UNPLUG

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Date:	Wed, 4 Jul 2012 12:49:05 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH WIP 2/5] xen/arm: set xen_platform_pci_unplug to
 XEN_UNPLUG_ALL

On Wed, 2012-07-04 at 12:27 +0100, Stefano Stabellini wrote:
> On Wed, 4 Jul 2012, David Vrabel wrote:
> > On 04/07/12 12:15, Stefano Stabellini wrote:
> > > Set xen_platform_pci_unplug to XEN_UNPLUG_ALL by default to make
> > > blkfront happy. The parameter doesn't make sense on ARM and should be
> > > removed.
> > 
> > Why is this parameter nonsensical on ARM?  ARM systems can have PCI devices.
> 
> Because we shouldn't assume the presence of a PCI bus on ARM. Moreover
> it would be nice to avoid the ugly unplug protocol entirely if we can.

Also "pci" here refers to the "platform_pci" device not to PCI devices
in general.

SO I think this option is indeed nonsensical at least until such a time
as we have HVM like ARM guests (i.e. ones with a DM emulating specific
platforms) which require a PCI device which serves as the "you are
running under Xen" hook intp to the non-PV aware OSes driver subsystem.
And it's not clear that when we have such guests that a platform pci
device will be the correct solution on ARM anyway.

Ian.


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