Re: [dpdk-dev] [EXT] Re: [PATCH] config/arm: add ability to express arch extensions

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

> -----Original Message-----
> From: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>
> Sent: Wednesday, May 12, 2021 11:18 AM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>;
> thomas@monjalon.net
> Cc: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Juraj Linkeš
> <juraj.linkes@pantheon.tech>; Jan Viktorin <viktorin@rehivetech.com>; Ruifeng
> Wang <Ruifeng.Wang@arm.com>; Bruce Richardson
> <bruce.richardson@intel.com>; dev@dpdk.org; nd <nd@arm.com>; nd
> <nd@arm.com>
> Subject: RE: [dpdk-dev] [EXT] Re: [PATCH] config/arm: add ability to express
> arch extensions
> 
> 
> ><snip>
> >
> >>
> >> >> >>
> >> >> >> >
> >> >> >> > The patch still holds true for CRC though as it is listed
> >> >> >> > separately below
> >> >> >> > https://urldefense.proofpoint.com/v2/url?u=https-
> >> >> >3A__developer.arm.com_architectures_cpu-2Darchitecture_a-
> >> >>
> >>2D&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=E3SgYMjtKCMVsB-
> >> >> >fmvgGV3o-
> >> >>
> >>
> >>>g_fjLhk5Pupi9ijohpc&m=i3kC8htMiHjXMoJWUn6QlDVZQCblbFrIJyMc
> >> >W
> >> >>
> >>
> >>>d9nAmM&s=fA4SM6O3iC2HXIK1qSbOHzxVeHoYqcfUebEOwioHC7c&
> >e
> >> >=
> >> >> >> > profile/exploration-tools/feature-names-for-a-profile
> >> >> >CRC is mandatory starting in V8.1, refer to Arm-ARM document.
> >> >> >
> >> >> >> >
> >> >> >> > Also, looks like sve2 support in n2 core might be optional as
> >> >> >> > per
> >> >> >above doc?
> >> >> >> I need to check on this. Some of the info here might not be
> >public
> >> >yet.
> >> >> >I found [1]. SVE2 is mandatory feature.
> >> >> >
> >> >>
> >> >> I see thanks for the info I will remove extension from cnxk.
> >> >>
> >> >> Do you think the extension infra is still useful for other cases? i.e.
> >> >older cores
> >> >> or cases where vendor wants to enable some extensions by
> >default?
> >> >>
> >> >> I found a document[1] which describes about extensions not
> >enabled
> >> >by
> >> >> default but supported by a given march.
> >> >> In case of n2 I think memory tagging is one such feature
> >> >I think the reference is providing a different information than what
> >> >you are trying to achieve here.
> >> >
> >> >It looks like you are trying to address a use case where in the same
> >> >CPU IP has different features enabled/disabled on different SoCs.
> >> >This is a valid use case from crypto perspective (due to export
> >control
> >> >reasons) where-in 2 different SoCs might have crypto
> >enabled/disabled.
> >> >I am not sure if other features can be enabled/disabled. But, Crypto
> >> >feature is a good enough reason to address such a use case.
> >>
> >> Yes, that's my intension apologies if the commit log doesn't clarify
> >> it
> >properly.
> >>
> >> >
> >> >IMO,  we should capture the SoC specific details in SoC specific
> >> >files, in this case in 'arm64_cn10k_linux_gcc'. I believe there were
> >> >some challenges in doing this.
> >>
> >> Since, all the flags are populated through soc_* variable and
> >> arm64_cn10k_linux_gcc also translates to soc_cn10k I believe the
> >extensions
> >> should be reported through
> >> soc_* variables.
> >IMO, there will be more SoCs in the future. I prefer to not grow
> >meson.build.
> 
> Problem is native build wouldn't read arm64_*_linux_gcc, it will be really hard to
> parse it and read extensions if they are placed there.
> 

Yes, this is the reason we have the SoC configuration in meson.build and not anywhere else. In meson 0.47.1, it was the only way to use SoC config in both native and cross builds. This implies that even these arch extension would need to in meson.build so that we could use those for both native and cross builds.

> >>
> >> Also, do you think +crypto needs to be removed from default n2
> >config as its
> >> optional?
> >Agree. Better to move it to SoC specific configuration.
> >
> >>
> >> >Juraj, do you remember the exact issue?
> >> >
> >> >>
> >> >> [1]https://urldefense.proofpoint.com/v2/url?u=https-
> >> >3A__developer.arm.com_tools-2Dand-2Dsoftware_open-2Dsource-
> >> >2D&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=E3SgYMjtKCMVsB-
> >> >fmvgGV3o-g_fjLhk5Pupi9ijohpc&m=0oZnXDnO-
> >>
> >>oYL9lESEaZt_nH_kK8Nc3m0tvdEPpKeFZc&s=WxrPoWhkM2QIFGEKezP
> >K
> >> >D9oEn7nGFvvgS2ul9ZYx-Kg&e=
> >> >> software/developer-tools/gnu-toolchain/architecture-support
> >> >>
> >> >>
> >> >> >[1] https://urldefense.proofpoint.com/v2/url?u=https-
> >> >> >3A__developer.arm.com_ip-
> >> >> >2Dproducts_processors_neoverse_neoverse-
> >> >>
> >>
> >>>2Dn2&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=E3SgYMjtKCMVs
> >B
> >> >-
> >> >> >fmvgGV3o-
> >> >>
> >>
> >>>g_fjLhk5Pupi9ijohpc&m=i3kC8htMiHjXMoJWUn6QlDVZQCblbFrIJyMc
> >> >W
> >> >> >d9nAmM&s=kP_X-Co0cl4pZ64BZqy5rAFUlkMZE-
> >> >3EhTVBabm3SW8&e=
> >> >> >
> >> >> ><snip>