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Date: Wed, 16 Jan 2013 16:17:16 +0000
From: Andrew Murray <andrew.murray@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Thierry Reding <thierry.reding@avionic-design.de>,
        Stephen Warren <swarren@wwwdotorg.org>,
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Subject: Re: [PATCH 10/14] PCI: tegra: Move PCIe driver to drivers/pci/host
Message-ID: <20130116161716.GA10630@arm.com>
References: <1357764194-12677-1-git-send-email-thierry.reding@avionic-design.de>
 <20130115154038.GA11241@arm.com>
 <20130115211441.GA13139@avionic-0098.adnet.avionic-design.de>
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On Wed, Jan 16, 2013 at 02:00:26PM +0000, Arnd Bergmann wrote:
> On Tuesday 15 January 2013, Thierry Reding wrote:
> > Is there actually hardware that supports this? I assumed that the MSI
> > controller would have to be tightly coupled to the PCI host bridge in
> > order to raise an interrupt when an MSI is received via PCI.
> 
> No, as long as it's guaranteed that the MSI notification won't arrive
> at the CPU before any inbound DMA data before it, the MSI controller
> can be anywhere. Typically, the MSI controller is actually closer to
> the CPU core than to the PCI bridge. On X86, I believe the MSI address
> is on normally on the the "local APIC" on each CPU.

MSIs are indistinguishable from other memory-write transactions originating
from the RC other than the address they target. Anything that can capture
that write in the address space (even a page fault) could be an MSI controller
and call interrupt handlers. And so the RC / MSI controllers don't need to
be aware of each other.

Andrew Murray