linux-kernel - Re: [PATCH v4] irq: add quirk for broken interrupt remapping on 55XX chipsets

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Message-ID: <20130405002405.GA24109@hmsreliant.think-freely.org>
Date:	Thu, 4 Apr 2013 20:24:05 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Don Dutile <ddutile@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Don Zickus <dzickus@...hat.com>,
	Asit Mallick <asit.k.mallick@...el.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v4] irq: add quirk for broken interrupt remapping on 55XX
 chipsets

On Thu, Apr 04, 2013 at 02:11:54PM -0700, Yinghai Lu wrote:
> On Thu, Apr 4, 2013 at 1:33 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> >> See my last email to Bjorn.  Doing this in early-quirks in such a way that we
> >> can detect an iommu that has interrupt remapping enabled (so we don't just
> >> unilaterally print this quirk all the time) requires that we be able to parse
> >> acpi tables very early in the boot.  If you know of how to do that, I can make
> >> this happen.  If not, I suppose another alternative would be to have the early
> >> quirk set a flag that tells us this is a bogus chip, and if we try to enable irq
> >> remapping with that flag set, we should fail, and report the error at that time,
> >> but I'm not sure I like that solution.
> >
> > I like that solution :)  It seems very simple -- you don't have to
> > parse any tables or anything.
> 
> You are right, we don't need to parse any acpi tables.
> 
> just add one quirk in early-quirk.c to set
>    disable_irq_remap = 1;
> 
Well, I can't just do that.  We need to issue a warning to the user as well, and
to do so conditionally (we don't want to warn users who have prorperly updated
BIOSes), I would need to know if irq remapping is actually on or not, which
would require parsing ACPI tables

But, as noted above, I can just set a flag, and defer the printing of the
warning until later in the boot process, when we know that information already.
Bjorn seems on board with that idea, so I'll spin up a patch for it in the AM.

Thanks!
Neil

> Thanks
> 
> Yinghai
> 
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