linux-kernel - Re: [PATCH 5/8] PCI PCIe portdrv: Fix allocation of interrupts

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Date:	Sat, 10 Jan 2009 00:38:56 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Linux PCI <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] PCI PCIe portdrv: Fix allocation of interrupts

On Saturday 10 January 2009, Jesse Barnes wrote:
> On Thursday, January 8, 2009 12:45 pm Rafael J. Wysocki wrote:
> > On Thursday 08 January 2009, Rafael J. Wysocki wrote:
> > > On Thursday 08 January 2009, Kenji Kaneshige wrote:
> > > > Rafael J. Wysocki wrote:
> > > > > On Thursday 08 January 2009, Kenji Kaneshige wrote:
> > > > >> Rafael J. Wysocki wrote:
> > > > >>> From: Rafael J. Wysocki <rjw@...k.pl>
> > > > >>>
> > > > >>> If MSI-X interrupt mode is used by the PCI Express port driver, too
> > > > >>> many vectors are allocated and it is not ensured that the right
> > > > >>> vectors will be used for various services.  Namely, the PCI Express
> > > > >>> specification states that both PCI Express native PME and PCI
> > > > >>> Express hotplug will always use the same MSI or MSI-X message for
> > > > >>> signalling interrupts, which implies that the same vector will be
> > > > >>> used by both of them.  Also, the VC service does not use interrupts
> > > > >>> at all. Moreover, is not clear which of the vectors allocated by
> > > > >>> pci_enable_msix() will be used for PME and hotplug and which of
> > > > >>> them will be used for AER if all of these services are configured.
> > > > >>>
> > > > >>> For these reasons, rework the allocation of interrupts for PCI
> > > > >>> Express ports so that at most two vectors are allocated and ensure
> > > > >>> that the right vector will be used for the right purpose.
> >
> > Appended is a cleaned-up version of the patch that also contains comments
> > with references to the appropriate sections of the PCI Express spec.
> 
> We'll need testing here in any case; I'll have to re-read the specs carefully 
> to see if we can really rely on the vector numbers you have here (at first 
> glance Kenji-san's approach seems more robust).

It has a catch too.  Namely, is there any warranty that we'll get the same
vectors when the second pci_enable_msix() is called and that they will be in
the same order?

Rafael
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