Messages in this thread | | | Subject | Re: [PATCH] fpga: region: handle compat_id as an uuid | From | Tom Rix <> | Date | Fri, 30 Jul 2021 05:07:00 -0700 |
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On 7/29/21 6:48 PM, Xu Yilun wrote: > On Thu, Jul 29, 2021 at 12:16:47PM -0700, Tom Rix wrote: >> On 7/29/21 11:51 AM, Moritz Fischer wrote: >>> 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? >> My gripe is >> >> For a nominally common interface, compat_id has a vendor specific output. >> >> If for example another vendor wanted to use this field but their natural >> format was an OF string. >> >> 16 bytes of raw hex would not work for them, so they would roll their own. >> >> which defeats the purpose of a common interface. >> >> >> The language in the docs as-is is vague on the output format. >> >> DFL is the only user of the interface. >> >> So ver 2 >> >> https://lore.kernel.org/linux-fpga/4ab7dd2d-c215-6333-6860-6f7d0ac64c3d@redhat.com/ >> >> Keeps the output as-is for dfl, so nothing breaks in userspace >> >> And adds flexibility for vendors to output their appropriate natural form. >> >> So compat_id becomes generally useful. > Mixing types seems be strongly against in Documentation/filesystems/sysfs.rst. > So in my opinion there should be a determined format for the output. The > concern for this patch is which one is a better format, uuid style or > 128 bit raw hex? > > And I vote for 128 bit raw hex, as other vendors may not use uuid_t as > the identifier, may be an OF string. So we don't have to force them > decorate it as the uuid style.
So you would be ok with v2 of this patchset ?
Tom
> > Thanks > Yilun > >> >> Tom >> >> >>> - Moritz >>>
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