linux-kernel - Re: [PATCH] x86 PCI: Do not use interrupt links for devices using MSI-X

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Message-ID: <20090107131348.GE3529@elte.hu>
Date:	Wed, 7 Jan 2009 14:13:48 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86 PCI: Do not use interrupt links for devices using
	MSI-X


* Jesse Barnes <jbarnes@...tuousgeek.org> wrote:

> On Monday, January 5, 2009 5:04 am Ingo Molnar wrote:
> > * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > From: Rafael J. Wysocki <rjw@...k.pl>
> > >
> > > pcibios_enable_device() and pcibios_disable_device() don't handle
> > > IRQs for devices that have MSI enabled and it should tread the
> >
> > s/tread/treat
> >
> > > devices with MSI-X enabled in the same way.
> > >
> > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > ---
> > >  arch/x86/pci/common.c |    4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > looks good - Jesse, what do you think?
> 
> Yeah, seems obviously correct, I'll queue it up.
> 
> > Rafael, i'm curious is this in response to some regression/bug? Did some
> > box or driver get confused by us enabling/disabling the GSI? Some IRQ
> > flood perhaps?
> >
> > btw., there's a small observation:
> > > +     if (!dev->msi_enabled && !dev->msix_enabled)
> >
> > maybe a "pci_has_gsi_irq()" wrapper would make these checks cleaner and
> > would make things more robust, should there be any new IRQ delivery method
> > be introduced in the future?
> 
> pci_has_msi_irq surely?  Otherwise we'll catch pretty much everything?  Or did 
> you mean !pci_has_gsi_irq() here instead?

Well - here the check is: "if (not MSI or MSIX)" in essence. I thought 
that it might be confusing to call it _msi() as well, so we could approach 
it via the inverse space: general system interrupts (GSIs) - which are 
device irqs that are neither MSI nor MSIX.

But if pci_has_msi_irq() can cleanly include the MSIX portion too, that's 
fine too. (MSI-X is really MSI with wider eventing capabilities but 
otherwise non-GSI just as much - and we dont want to enable (or even 
touch) the legacy IRQ line registers for any of them, even if they happen 
to be enumerated)

Right?

	Ingo
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