linux-kernel - Re: [PATCH 1/7] powerpc: Add interface to get msi region information

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Message-ID: <1381275325.7979.320.camel@snotra.buserror.net>
Date:	Tue, 8 Oct 2013 18:35:25 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Bharat Bhushan <r65777@...escale.com>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	Joerg Roedel <joro@...tes.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Kumar Gala <galak@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Alexander Graf <agraf@...e.de>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux-foundation.org>,
	Bharat Bhushan <Bharat.Bhushan@...escale.com>
Subject: Re: [PATCH 1/7] powerpc: Add interface to get msi region information

On Tue, 2013-10-08 at 17:25 -0600, Bjorn Helgaas wrote:
> >> -     u32 msiir_offset; /* Offset of MSIIR, relative to start of CCSR */
> >> +     dma_addr_t msiir; /* MSIIR Address in CCSR */
> >
> > Are you sure dma_addr_t is right here, versus phys_addr_t?  It implies
> > that it's the output of the DMA API, but I don't think the DMA API is
> > used in the MSI driver.  Perhaps it should be, but we still want the raw
> > physical address to pass on to VFIO.
> 
> I don't know what "msiir" is used for, but if it's an address you
> program into a PCI device, then it's a dma_addr_t even if you didn't
> get it from the DMA API.  Maybe "bus_addr_t" would have been a more
> suggestive name than "dma_addr_t".  That said, I have no idea how this
> relates to VFIO.

It's a bit awkward because it gets used both as something to program
into a PCI device (and it's probably a bug that the DMA API doesn't get
used), and also (if I understand the current plans correctly) as a
physical address to give to VFIO to be a destination address in an IOMMU
mapping.  So I think the value we keep here should be a phys_addr_t (it
comes straight from the MMIO address in the device tree), which gets
trivially turned into a dma_addr_t by the non-VFIO code path because
there's currently no translation there.

-Scott



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