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    SubjectRe: [PATCH v3 1/2] iommu - Enable debugfs exposure of the IOMMU
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    On 17/04/18 18:46, Hook, Gary wrote:
    > On 4/6/2018 9:17 AM, Gary R Hook wrote:
    >> Provide base enablement for using debugfs to expose internal data of
    >> an IOMMU driver. When called, create the /sys/kernel/debug/iommu
    >> directory.  Emit a strong warning at boot time to indicate that this
    >> feature is enabled.
    >>
    >> This patch adds a top-level function that will create the (above)
    >> directory, under which a driver may create a hw-specific directory for
    >> its use. The function
    >>
    >>     iommu_debugfs_setup()
    >>
    >> returns a pointer to the new dentry structure created for
    >> /sys/kernel/debug/iommu, or NULL in the event of a failure. An IOMMU
    >> driver should call this function first, and then create a directory
    >> beneath it. A driver implementation might look something like:
    >>
    >> static struct dentry *my_debugfs;
    >>
    >>     struct dentry *d_top;
    >>     if (!my_debugfs) {
    >>         d_top = iommu_debugfs_setup();
    >>         if (d_top)
    >>             my_debugfs = debugfs_create_dir("vendor", d_top);
    >>     }
    >>
    >> Since the IOMMU driver can not be removed from the running system, this
    >> patch only provides an "on" function.
    >>
    >> Signed-off-by: Gary R Hook <gary.hook@amd.com>
    >> ---
    >>   drivers/iommu/Kconfig         |   11 ++++++++
    >>   drivers/iommu/Makefile        |    1 +
    >>   drivers/iommu/iommu-debugfs.c |   58
    >> +++++++++++++++++++++++++++++++++++++++++
    >>   include/linux/iommu.h         |    4 +++
    >>   4 files changed, 74 insertions(+)
    >>   create mode 100644 drivers/iommu/iommu-debugfs.c
    >>
    >> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
    >> index f3a21343e636..c1e39dabfec2 100644
    >> --- a/drivers/iommu/Kconfig
    >> +++ b/drivers/iommu/Kconfig
    >> @@ -60,6 +60,17 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
    >>   endmenu
    >> +config IOMMU_DEBUG
    >> +    bool "Enable IOMMU internals in DebugFS"
    >> +    depends on DEBUG_FS
    >> +    default n
    >> +    help
    >> +      Allows exposure of IOMMU device internals. This option enables
    >> +      the use of debugfs by IOMMU drivers as required. Devices can,
    >> +      at initialization time, cause the IOMMU code to create a top-level
    >> +      debug/iommu directory, and then populate a subdirectory with
    >> +      entries as required.
    >
    > I should explicitly ask about this:
    >
    > Joerg had suggested IOMMU_DEBUGFS, but here I've changed to IOMMU_DEBUG.
    > I'm not seeing a lot of CONFIG options that use DEBUGFS for debugfs
    > options, so I chose to follow an implied convention.
    >
    > Question: should this indeed be IOMMU_DEBUGFS?
    >                                 ^^^^^^^^^^^^^

    Personally I'd say yes, since there is at least some precedent for
    *_DEBUGFS already, and it does help make the intent that much clearer
    (*_DEBUG often just means lots of dmesg spam rather than an actual
    debugfs interface).

    Robin.

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