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    SubjectRe: [PATCH -mm 0/11] fix iommu sg merging problem
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    On Wed, 24 Oct 2007 07:40:50 -0400
    Jeff Garzik <jeff@garzik.org> wrote:

    > FUJITA Tomonori wrote:
    > > IOMMUs merges scatter/gather segments without considering a low level
    > > driver's restrictions. The problem is that IOMMUs can't access to the
    > > limitations because they are in request_queue.
    > >
    > > This patchset introduces a new structure, device_dma_parameters,
    > > including dma information. A pointer to device_dma_parameters is added
    > > to struct device. The bus specific structures (like pci_dev) includes
    > > device_dma_parameters. Low level drivers can use dma_set_max_seg_size
    > > to tell IOMMUs about the restrictions.
    > >
    > > We can move more dma stuff in struct device (like dma_mask) to struct
    > > device_dma_parameters later (needs some cleanups before that).
    > >
    > > This includes patches for all the IOMMUs that could merge sg (x86_64,
    > > ppc, IA64, alpha, sparc64, and parisc) though only the ppc patch was
    > > tested. The patches for other IOMMUs are only compile tested.
    > >
    > > Thanks to everyone for the comments on the previous submission
    > > to linux-scsi.
    > >
    > > This is against 2.6.24-rc1. The same patchset is also available:
    > >
    > > git://git.kernel.org/pub/scm/linux/kernel/git/tomo/linux-2.6-misc.git iommu-sg-fixes
    >
    > Are you interested in collecting patches to libata that eliminate the
    > hand-rolled S/G splitting? e.g. now ata_fill_sg() and mv_fill_sg() can
    > be made much more efficient.

    Yeah, but ATA has the segment boundary limit too. It's much more
    tricky than the segment size limit. It makes the IOMMU free space
    managemet complicated.


    > Again, thanks for doing this! It's been needed for a long time.

    My pleasure.
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