linux-kernel - Re: [PATCH 1/2] pci: add misrouted interrupt error handling

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Date:	Tue, 05 Aug 2008 13:56:34 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 1/2] pci: add misrouted interrupt error handling

On Tue, 2008-08-05 at 13:53 -0700, Jesse Barnes wrote:
> On Tuesday, August 05, 2008 1:44 pm James Bottomley wrote:
> > On Tue, 2008-08-05 at 10:03 -0700, Jesse Barnes wrote:
> > > This seems to be a function that just returns what type of IRQ you're
> > > using or how it's routed and it isn't necessarily "lost interrupt"
> > > specific.
> >
> > So perhaps this routine should only note but not advise?  The drivers
> > can then just call pci_interrupt_type to see if they can do anything.
> 
> If it's just a pci_irq_type function then it probably shouldn't print 
> anything, and leave that to the caller, since it might be used for other 
> purposes too (e.g. a driver load printk or something).  In the lost interrupt 
> case you already have to disable MSI or MSIX in the Fusion driver, so you may 
> as well put the printk there, right?  I guess I'm saying it should neither 
> note nor advise, just return the IRQ type.

Well, no; the object was to have the layer that knew (PCI) print
information which could be used to identify the problem.  Likely what
the driver will say is something like "MSI isn't working and it's not my
fault".  What I want is for PCI to print something that may be helpful
to people trying to diagnose the problem.  Driver writers aren't going
to get that right.

> > > This information is clearly useful to drivers both for informational
> > > purposes and for debugging problems, so on that front it looks good. 
> > > However, I think it should probably be called pci_interrupt_type(struct
> > > pci_dev *dev) or something instead, and just return an enum of either
> > > MSIX, MSI, or LINE (though I'm open to better names).  From that, the
> > > driver can infer what might be going wrong, though in the case of a LINE
> > > interrupt, all you can really do is report that there's probably a
> > > platform IRQ routing problem.
> >
> > The only thing that this can't do is ACPI ... but on the other hand once
> > the IRQ routing is set by ACPI I'm not sure the driver can do anything
> > to fix it.
> 
> Yeah, ACPI may or may not be the problem, all you'll really know is that 
> you've got a line interrupt that you failed to get...  The driver won't be 
> able to do much in that case aside from complain loudly.

Yes ... it's just that when line interrupts fail (especially if they
worked previously) it's usually ACPI to blame.

James


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