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    SubjectRe: [PATCH] fpga: region: handle compat_id as an uuid
    On Wed, Jul 28, 2021 at 01:36:56AM +0000, Wu, Hao wrote:
    > > On 7/26/21 3:12 PM, Russ Weight wrote:
    > > > On 7/26/21 1:26 PM, trix@redhat.com wrote:
    > > >> From: Tom Rix <trix@redhat.com>
    > > >>
    > > >> An fpga region's compat_id is exported by the sysfs
    > > >> as a 128 bit hex string formed by concatenating two
    > > >> 64 bit values together.
    > > >>
    > > >> The only user of compat_id is dfl. Its user library
    > > >> opae converts this value into a uuid.
    > > >>
    > > >> ex/
    > > >> $ cat /sys/class/fpga_region/region1/compat_id
    > > >> f3c9941350814aadbced07eb84a6d0bb
    > > >>
    > > >> Is reported as
    > > >> $ fpgainfo bmc
    > > >> ...
    > > >> Pr Interface Id : f3c99413-5081-4aad-bced-07eb84a6d0bb
    > > >>
    > > >> Storing a uuid as 2 64 bit values is vendor specific.
    > > >> And concatenating them together is vendor specific.
    > > >>
    > > >> It is better to store and print out as a vendor neutral uuid.
    > > >>
    > > >> Change fpga_compat_id from a struct to a union.
    > > >> Keep the old 64 bit values for dfl.
    > > >> Sysfs output is now
    > > >> f3c99413-5081-4aad-bced-07eb84a6d0bb
    > > > I'm fowarding feedback from Tim Whisonant, one of the OPAE userspace
    > > > developers:
    > > >
    > > > I think that this change to the sysfs for the compat_id node will
    > > > end up breaking the SDK, which does not expect the '-' characters to
    > > > be included when parsing the sysfs value. Currently, it is parsed as
    > > > a raw hex string without regard to any '-' characters. This goes for
    > > > any "guid" currently exported by sysfs and for what we read in the
    > > > device MMIO space.
    > >
    > > Yes, it will.
    > >
    > > And there are other places, like dfl-afu-main.c:afu_id_show()
    > >
    > > outputs raw hex that sdk turns into a uuid.
    > >
    > >
    > > Some options.
    > >
    > > If no one but dfl will ever use it, then v1 of patchset.
    > >
    > > If others can use it but don't want to change dfl, then v2 of patchset,
    > > my favorite.
    > >
    > > Or this one for uuid for everyone, what have been v3 but changed too much.
    > >
    > >
    > > could dfl change generally to output uuid's to the sysfs ?
    > >
    > > this would be generally helpful and a one time disruption to the sdk.
    >
    > This change limited the output format to uuid_t, but if any hardware doesn't
    > use uuid_t on hardware may have to convert it back from the sysfs output in
    > userspace. Leave it to print hardware values (e.g. from register), and convert
    > it in userspace should be fine too I think.

    I'm not entirely sure. I seem to recall there being examples of sysfs
    files returning different things for different drivers.

    That being said it seems largely cosmetic to add the '-' in between.

    If it breaks userspace, I'm against it. If you *need* it make a
    compat_uuid entry or something in that case?

    - Moritz

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