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Subject: Re: [PATCH 1/4] pci/msi: Move "force_32bit_msi" flag from powerpc
 to generic pci_dev
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Bjorn Helgaas <bhelgaas@google.com>
Cc: Alex Deucher <alexdeucher@gmail.com>,
	Dave Airlie <airlied@linux.ie>,
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Date: Thu, 02 Oct 2014 08:09:50 +1000
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On Wed, 2014-10-01 at 14:33 -0600, Bjorn Helgaas wrote:
> I like the idea of handling this more generically, e.g., with a bit like
> this in struct pci_dev (I'd probably name it something like "no_64bit_msi"
> along the lines of your driver #defines).
> 
> What I don't like is that we haven't done anything to help other
> architectures, because the only code that *looks* at this bit is in
> arch/powerpc.  The next arch that tries to use 64-bit MSI addresses for
> these devices will trip over the same problem.

I started looking. From my (limited) understanding of x86, it doesn't
even look at the "size" of MSIs which makes me think it's always 32-bit,
and I plan to look at the others next (though not for stable).

> Can we check in pci_enable_msi_range() and pci_enable_msix_range() whether
> the MSI addresses allocated by the arch are too big, and fail the call if
> they are?

Yes, good idea, I'll add something.

Cheers,
Ben.