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    SubjectRe: [RFC patch] init default dma_ops to prepare intel_iommu_init failure
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    On Wed, 12 Aug 2009 11:17:22 -0700
    Fenghua Yu <fenghua.yu@intel.com> wrote:

    > > Hi there,
    > >
    > > On ia64 platform with dmar table and new upstream
    > > kernel(config_dmar_default_on enabled),
    > > if intel_iommu_init ends up without dma_ops initialized or other iommu
    > > failures.
    > > We got nothing to fall back. The following patch fixes it.
    > >
    > x86/x86-64 also needs this fix. Please check the pci_swiotlb_init for x86/64.

    x86 falls back into nommu_dam_ops (though it would be better to use
    swiotlb on x86_64).


    > > Please review. If make sense, please apply.
    > >
    > > **The patch is enclosed in text attachment*
    > > **Using web client to send the patch* *
    > > **below is for review, please apply attached patch*/
    > >
    > > Thanks,
    > > Luming
    > >
    > > Signed-off-by: Yu Luming <luming.yu@intel.com>
    > >
    > > arch/ia64/kernel/pci-swiotlb.c | 14 ++++++--------
    > > 1 file changed, 6 insertions(+), 8 deletions(-)
    > >
    > > diff --git a/arch/ia64/kernel/pci-swiotlb.c b/arch/ia64/kernel/pci-swiotlb.c
    > > index 223abb1..d5dcaf5 100644
    > > --- a/arch/ia64/kernel/pci-swiotlb.c
    > > +++ b/arch/ia64/kernel/pci-swiotlb.c
    > > @@ -46,15 +46,13 @@ void __init swiotlb_dma_init(void)
    > >
    > > void __init pci_swiotlb_init(void)
    > > {
    > > - if (!iommu_detected || iommu_pass_through) {
    >
    > This check can not be removed. Otherwise, swiotlb_dma_ops will always override
    > previous dma_ops value.

    Yeah.


    > I think you can change this check to something like:
    > if (!dma_ops || iommu_pass_through) {

    I don't think this work since pci_iommu_alloc() always sets up dma_ops
    and calls pci_swiotlb_init().

    All we need to do here is calling swiotlb_init() then we can use
    swiotlb_dma_ops after intel_iommu_init() fails:

    http://marc.info/?l=linux-kernel&m=125013354518721&w=2


    > With this change, checking iommu_detected is unnecesary because checking dma_ops
    > covers it.
    >
    > > #ifdef CONFIG_IA64_GENERIC
    > > - swiotlb = 1;
    > > - printk(KERN_INFO "PCI-DMA: Re-initialize machine vector.\n");
    > > - machvec_init("dig");
    > > - swiotlb_init();
    > > - dma_ops = &swiotlb_dma_ops;
    > > + swiotlb = 1;
    > > + printk(KERN_INFO "PCI-DMA: Re-initialize machine vector.\n");
    > > + machvec_init("dig");
    > > + swiotlb_init();
    > > + dma_ops = &swiotlb_dma_ops;
    > > #else
    > > - panic("Unable to find Intel IOMMU");
    > > + panic("Unable to find Intel IOMMU");
    > > #endif
    > > - }
    > > }
    >
    >
    >
    > --
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