linux-kernel - Re: [PATCH 04/13] pci: New pci_dma

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Date:	Thu, 17 May 2012 09:22:00 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Anonymous <anonymous@...ebluemarble.com>
Cc:	benh@...nel.crashing.org, aik@...abs.ru,
	david@...son.dropbear.id.au, joerg.roedel@....com,
	dwmw2@...radead.org, kvm@...r.kernel.org, B07421@...escale.com,
	linux-pci@...r.kernel.org, agraf@...e.de, qemu-devel@...gnu.org,
	chrisw@...s-sol.org, B08248@...escale.com,
	iommu@...ts.linux-foundation.org, avi@...hat.com,
	gregkh@...uxfoundation.org, bhelgaas@...gle.com,
	linux-kernel@...r.kernel.org, benve@...co.com
Subject: Re: [PATCH 04/13] pci: New pci_dma_quirk()

On Thu, 2012-05-17 at 15:19 +0800, Anonymous wrote:
> Alex,
> 
> On Sat, May 12, 2012 at 6:55 AM, Alex Williamson
> <alex.williamson@...hat.com> wrote:
> > Integrating IOMMU groups more closely into the driver core allows
> > us to more easily work around DMA quirks.  The Ricoh multifunction
> > controller is a favorite example of devices that are currently
> > incompatible with IOMMU isolation as all the functions use the
> > requestor ID of function 0 for DMA.  Passing this device into
> > pci_dma_quirk returns the PCI device to use for DMA.  The IOMMU
> > driver can then construct an IOMMU group including both devices.
> >
> 
> Please give some thought to the Marvell SATA controller quirk as well.
> 
> Instead of multiple visible functions using the same requester ID of
> function 0, the Marvell device only makes function 0 visible, but uses
> the requestor ID of function 1 as well during DMA.
> 
> See https://bugzilla.redhat.com/show_bug.cgi?id=757166

Wow.  That one isn't quite as easy to deal with since there's no
existing device in the kernel to point to.  This comment might be on the
right track:

https://bugzilla.kernel.org/show_bug.cgi?id=42679#c11

Perhaps David Woodhouse can comment on support for phantom functions.
If we had infrastructure for that it might be easy for the quirk to
update the pci_dev struct, inserting a new phantom function.  Otherwise
we'd need to create a new device in the kernel for it.  Thanks,

Alex


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