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    SubjectRe: [PATCH -tip] x86: fix iommu=soft boot option
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    On Mon, 30 Nov 2009 23:42:00 -0800
    Yinghai Lu <yinghai@kernel.org> wrote:

    > FUJITA Tomonori wrote:
    > > On Thu, 26 Nov 2009 23:45:33 -0800
    > > Yinghai Lu <yinghai@kernel.org> wrote:
    > >
    > >>>> when AMD64 mem > 4g, no AGP, BIOS set all gart iommu on all nodes size to 32M, and enable bit are set.
    > >>> I have such machine (with sane BIOS).
    > >>>
    > >>> But if BIOS is broken, early_gart_iommu_check() disables GART_EN bit
    > >>> (bits 0)?
    > >> not for 32M small size.
    > >>
    > >> that function only clear that bit when different nodes have different setting.
    > >>
    > >>>> 1. iommu=soft, will go through POINT A and POINT B
    > >>> Not always. if aperture_valid() is true, it doesn't go POINT A. My
    > >>> GART machine doesn't go.
    > >> maybe your bios set GART iommu set to 64M?
    > >
    > > Yeah, my machine has sane BIOS.
    > >
    > >
    > >>>> 2. no "iommu=soft", will go through POINT A and POINT C
    > >>> As I said, it's not true about POINT A.
    > >> maybe your bios set GART iommu set to 64M?
    > >>
    > >>>
    > >>>> and all will reach POINT X to make sure ENABLE bit is not set.
    > >>> POINT X doesn't look make sure ENABLE bit is not set. It just fixes up
    > >>> (sets) the address and its size.
    > >> write_pci_config(bus, slot, 3, AMD64_GARTAPERTURECTL, aper_order << 1);
    > >>
    > >> that bit is that bit 0 of AMD64_GARTAPERTURECTL reg.
    > >
    > > Oops, thanks.
    > >
    > > But as I wrote in the previous mail, can you tell me why we need this?
    > > With 2.6.31 my machine uses swiotlb with GART_EN bit enabled.
    > >
    > > My another question is that why can't early_gart_iommu_check()
    > > _always_ disable GART_EN bit?
    >
    > please check

    Thanks.

    As I said, it looks cleaner if early_gart_iommu_check() disables
    GART_EN bit. So this patch looks better but I still have some
    questions.


    > [PATCH] x86: fix gart iommu using for amd 64 bit system -v4
    >
    > after
    > |commit 75f1cdf1dda92cae037ec848ae63690d91913eac
    > |Author: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
    > |Date: Tue Nov 10 19:46:20 2009 +0900
    > |
    > | x86: Handle HW IOMMU initialization failure gracefully
    > |
    > | If HW IOMMU initialization fails (Intel VT-d often does this,
    > | typically due to BIOS bugs), we fall back to nommu. It doesn't
    > | work for the majority since nowadays we have more than 4GB
    > | memory so we must use swiotlb instead of nommu.
    > ...
    >
    > amd 64 systems that
    > 1. do not have AGP
    > 2. do not have IOMMU
    > 3. mem > 4g
    > 4. BIOS do not allocate correct gart in NB.
    > will leave them to use SWIOTLB forcely.

    As I asked earlier, can you tell me what dma ops such system is
    supposed to use?


    > also in pci_iommu_alloc()
    > pci_swiotlb_init is stealing the preallocate range that is for
    > gart_iommu_hole workaround.
    >
    > so restore the sequence...
    >
    > will get back
    > [ 0.000000] Your BIOS doesn't leave a aperture memory hole
    > [ 0.000000] Please enable the IOMMU option in the BIOS setup
    > [ 0.000000] This costs you 64 MB of RAM
    > [ 0.000000] Mapping aperture over 65536 KB of RAM @ 20000000
    > ...
    > [ 12.702822] calling pci_iommu_init+0x0/0x31 @ 1
    > [ 12.708728] PCI-DMA: Disabling AGP.
    > [ 12.712812] PCI-DMA: aperture base @ 20000000 size 65536 KB
    > [ 12.718384] PCI-DMA: using GART IOMMU.
    > [ 12.722139] PCI-DMA: Reserving 64MB of IOMMU area in the AGP aperture
    > [ 12.736944] initcall pci_iommu_init+0x0/0x31 returned 0 after 28802 usecs
    >
    > -v2: call shutdown when no agp is there

    Is this change related with my above patchset?


    > -v3: add check_store to restore state for swiotlb
    > separate pci_swiotlb_detect and pci_swiotlb_init from FUJITA
    > -v4: disable translating in early_gart_iommu_check according to FUJITA

    Why can't we always disable translation in early_gart_iommu_check? We
    really need search_agp_bridge() in early_gart_iommu_check()?


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