linux-kernel - Re: [Xen-devel] [PATCH 1/3] pci/xen: Use xen_allocate_pirq

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Date:	Fri, 18 Feb 2011 14:13:08 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Ian Campbell <Ian.Campbell@...citrix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
Subject: Re: [Xen-devel] [PATCH 1/3] pci/xen: Use xen_allocate_pirq_msi

On Fri, 18 Feb 2011, Ian Campbell wrote:
> On Fri, 2011-02-18 at 14:07 +0000, Konrad Rzeszutek Wilk wrote:
> > On Thu, Feb 17, 2011 at 09:30:03AM -0500, Konrad Rzeszutek Wilk wrote:
> > > On Thu, Feb 17, 2011 at 08:41:31AM +0000, Ian Campbell wrote:
> > > > On Wed, 2011-02-16 at 22:17 +0000, Konrad Rzeszutek Wilk wrote:
> > > > > There is no need to use the old interface.
> > > > 
> > > > xen_allocate_pirq -> xen_map_pirq_gsi -> PHYSDEVOP_alloc_irq_vector IFF
> > > > xen_initial_domain() in addition to the kernel side book-keeping side of
> > > > things (set chip and handler, update irq_info etc) whereas
> > > > xen_allocate_pirq_msi just does the kernel book keeping.
> > > > 
> > > > Also xen_allocate_pirq allocates an IRQ in the 1-1 GSI space whereas
> > > > xen_allocate_pirq_msi allocates a dynamic one in the >GSI IRQ space.
> > > 
> > > Which is OK. These are MSIs.
> > > > 
> > > > So this change is actually a semantic change and not just a switch to a
> > > > new interface. I think the change is OK (because the caller is domU
> > > 
> > > Right.
> > > 
> > > > only?) but a comment explaining this would be appreciated.
> > > 
> > > Correct: "domU side".
> > > 
> > > Will fix it up.
> > 
> > How does this look to you?
> > 
> > From eb832bece3131ecbdb509f7f2a9bc53f6692177c Mon Sep 17 00:00:00 2001
> > From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Date: Wed, 16 Feb 2011 13:43:04 -0500
> > Subject: [PATCH 3/5] pci/xen: Use xen_allocate_pirq_msi instead of xen_allocate_pirq
> > 
> > xen_allocate_pirq -> xen_map_pirq_gsi -> PHYSDEVOP_alloc_irq_vector IFF
> > xen_initial_domain() in addition to the kernel side book-keeping side of
> > things (set chip and handler, update irq_info etc) whereas
> > xen_allocate_pirq_msi just does the kernel book keeping.
> > 
> > Also xen_allocate_pirq allocates an IRQ in the 1-1 GSI space whereas
> > xen_allocate_pirq_msi allocates a dynamic one in the >GSI IRQ space.
> > 
> > All of this is uneccessary as this code path is only executed
> > when we run as a domU PV guest with an MSI/MSI-X PCI card passed in.
> > Hence we can jump straight to allocating an dynamic IRQ (and
> > binding it to the proper PIRQ) and skip the rest.
> > 
> > In short: this change is a cosmetic one.
> > 
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> 
> Looks good,
> 
> Reviewed-by: Ian Campbell <ian.campbell@...rix.com>

You can add my reviewed-by too.

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