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    Subject[PATCH] iommu/amd: Fix event counter availability check
    Date
    The driver performs an extra check if the IOMMU's capabilities advertise
    presence of performance counters: it verifies that counters are writable
    by writing a hard-coded value to a counter and testing that reading that
    counter gives back the same value.

    Unfortunately it does so quite early, even before pci_enable_device is
    called for the IOMMU, i.e. when accessing its MMIO space is not
    guaranteed to work. On Ryzen 4500U CPU, this actually breaks the test:
    the driver assumes the counters are not writable, and disables the
    functionality.

    Moving init_iommu_perf_ctr just after iommu_flush_all_caches resolves
    the issue. This is the earliest point in amd_iommu_init_pci where the
    call succeeds on my laptop.

    Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
    Cc: Joerg Roedel <joro@8bytes.org>
    Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
    Cc: iommu@lists.linux-foundation.org
    ---

    PS. I'm seeing another hiccup with IOMMU probing on my system:
    pci 0000:00:00.2: can't derive routing for PCI INT A
    pci 0000:00:00.2: PCI INT A: not connected

    Hopefully I can figure it out, but I'd appreciate hints.

    drivers/iommu/amd_iommu_init.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
    index 5b81fd16f5fa..1b7ec6b6a282 100644
    --- a/drivers/iommu/amd_iommu_init.c
    +++ b/drivers/iommu/amd_iommu_init.c
    @@ -1788,8 +1788,6 @@ static int __init iommu_init_pci(struct amd_iommu *iommu)
    if (iommu->cap & (1UL << IOMMU_CAP_NPCACHE))
    amd_iommu_np_cache = true;

    - init_iommu_perf_ctr(iommu);
    -
    if (is_rd890_iommu(iommu->dev)) {
    int i, j;

    @@ -1891,8 +1889,10 @@ static int __init amd_iommu_init_pci(void)

    init_device_table_dma();

    - for_each_iommu(iommu)
    + for_each_iommu(iommu) {
    iommu_flush_all_caches(iommu);
    + init_iommu_perf_ctr(iommu);
    + }

    if (!ret)
    print_iommu_info();
    base-commit: 75caf310d16cc5e2f851c048cd597f5437013368
    --
    2.26.2

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