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    SubjectRe: [PATCH v3] iommu/vt-d: Make DMAR_UNITS_SUPPORTED a config setting
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    On 2022/6/16 02:36, Steve Wahl wrote:
    > To support up to 64 sockets with 10 DMAR units each (640), make the
    > value of DMAR_UNITS_SUPPORTED adjustable by a config variable,
    > CONFIG_DMAR_UNITS_SUPPORTED, and make it's default 1024 when MAXSMP is
    > set.
    >
    > If the available hardware exceeds DMAR_UNITS_SUPPORTED (previously set
    > to MAX_IO_APICS, or 128), it causes these messages: "DMAR: Failed to
    > allocate seq_id", "DMAR: Parse DMAR table failure.", and "x2apic: IRQ
    > remapping doesn't support X2APIC mode x2apic disabled"; and the system
    > fails to boot properly.
    >
    > Signed-off-by: Steve Wahl<steve.wahl@hpe.com>
    > Reviewed-by: Kevin Tian<kevin.tian@intel.com>
    > ---
    >
    > Note that we could not find a reason for connecting
    > DMAR_UNITS_SUPPORTED to MAX_IO_APICS as was done previously. Perhaps
    > it seemed like the two would continue to match on earlier processors.
    > There doesn't appear to be kernel code that assumes that the value of
    > one is related to the other.
    >
    > v2: Make this value a config option, rather than a fixed constant. The default
    > values should match previous configuration except in the MAXSMP case. Keeping the
    > value at a power of two was requested by Kevin Tian.
    >
    > v3: Make the config option dependent upon DMAR_TABLE, as it is not used without this.
    >
    > drivers/iommu/intel/Kconfig | 7 +++++++
    > include/linux/dmar.h | 6 +-----
    > 2 files changed, 8 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
    > index 39a06d245f12..07aaebcb581d 100644
    > --- a/drivers/iommu/intel/Kconfig
    > +++ b/drivers/iommu/intel/Kconfig
    > @@ -9,6 +9,13 @@ config DMAR_PERF
    > config DMAR_DEBUG
    > bool
    >
    > +config DMAR_UNITS_SUPPORTED
    > + int "Number of DMA Remapping Units supported"
    > + depends on DMAR_TABLE
    > + default 1024 if MAXSMP
    > + default 128 if X86_64
    > + default 64

    With this patch applied, the IOMMU configuration looks like:

    [*] AMD IOMMU support
    <M> AMD IOMMU Version 2 driver
    [*] Enable AMD IOMMU internals in DebugFS
    (1024) Number of DMA Remapping Units supported <<<< NEW
    [*] Support for Intel IOMMU using DMA Remapping Devices
    [*] Export Intel IOMMU internals in Debugfs
    [*] Support for Shared Virtual Memory with Intel IOMMU
    [*] Enable Intel DMA Remapping Devices by default
    [*] Enable Intel IOMMU scalable mode by default
    [*] Support for Interrupt Remapping
    [*] OMAP IOMMU Support
    [*] Export OMAP IOMMU internals in DebugFS
    [*] Rockchip IOMMU Support

    The NEW item looks confusing. It looks to be a generic configurable
    value though it's actually Intel DMAR specific. Any thoughts?

    Best regards,
    baolu

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