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From: Moritz Fischer <mdf@kernel.org>
To: "Wu, Hao" <hao.wu@intel.com>
Cc: Tom Rix <trix@redhat.com>,
	"Weight, Russell H" <russell.h.weight@intel.com>,
	"mdf@kernel.org" <mdf@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-fpga@vger.kernel.org" <linux-fpga@vger.kernel.org>
Subject: Re: [PATCH] fpga: region: handle compat_id as an uuid
Date: Thu, 29 Jul 2021 11:51:23 -0700	[thread overview]
Message-ID: <YQL4qyAmqj322HTz@epycbox.lan> (raw)
In-Reply-To: <DM6PR11MB38199F872DC94971D9C8A53885EA9@DM6PR11MB3819.namprd11.prod.outlook.com>

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

  reply	other threads:[~2021-07-29 18:51 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 20:26 trix
2021-07-26 22:12 ` Russ Weight
2021-07-27  0:16   ` Tom Rix
2021-07-28  1:36     ` Wu, Hao
2021-07-29 18:51       ` Moritz Fischer [this message]
2021-07-29 19:16         ` Tom Rix
2021-07-30  1:48           ` Xu Yilun
2021-07-30 12:07             ` Tom Rix
2021-08-03  3:32               ` Xu Yilun
2021-08-03 12:21                 ` Tom Rix
2021-08-04  1:44                   ` Xu Yilun
2021-08-04 13:21                     ` Tom Rix
2021-08-06  1:42                       ` Xu Yilun
2021-07-26 23:35 ` kernel test robot

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