linux-kernel - Re: [PATCH 10/14] PCI: tegra: Move PCIe driver to drivers/pci/host

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Message-ID: <20130116161716.GA10630@arm.com>
Date:	Wed, 16 Jan 2013 16:17:16 +0000
From:	Andrew Murray <andrew.murray@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Thierry Reding <thierry.reding@...onic-design.de>,
	Stephen Warren <swarren@...dotorg.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 10/14] PCI: tegra: Move PCIe driver to drivers/pci/host

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

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