RE: [PATCH] config/arm: fix Neoverse N2 march flag

[Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>]

> -----Original Message-----
> From: Ruifeng Wang <Ruifeng.Wang@arm.com>
> Sent: Thursday, June 8, 2023 4:12 PM
> To: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>; Jerin Jacob
> Kollanukkaran <jerinj@marvell.com>; Bruce Richardson
> <bruce.richardson@intel.com>
> Cc: dev@dpdk.org; Juraj Linkeš <juraj.linkes@pantheon.tech>; nd
> <nd@arm.com>
> Subject: [EXT] RE: [PATCH] config/arm: fix Neoverse N2 march flag
> 
> External Email
> 
> ----------------------------------------------------------------------
> > -----Original Message-----
> > From: pbhagavatula@marvell.com <pbhagavatula@marvell.com>
> > Sent: Thursday, June 8, 2023 3:28 PM
> > To: jerinj@marvell.com; Ruifeng Wang <Ruifeng.Wang@arm.com>; Bruce
> Richardson
> > <bruce.richardson@intel.com>
> > Cc: dev@dpdk.org; Pavan Nikhilesh <pbhagavatula@marvell.com>
> > Subject: [PATCH] config/arm: fix Neoverse N2 march flag
> >
> > From: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >
> > The -march flag of Neoverse N2 should be `armv9-a` when used along with
> -mcpu=neoverse-n2.
> >
> > Fixes: ea85ed1f6882 ("config/arm: increase nodes and cores for Neoverse
> N2")
> >
> > Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> > ---
> >  config/arm/meson.build | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/config/arm/meson.build b/config/arm/meson.build index
> 43f6a551a2..d3b4b4917f
> > 100644
> > --- a/config/arm/meson.build
> > +++ b/config/arm/meson.build
> > @@ -89,7 +89,7 @@ part_number_config_arm = {
> >          'march': 'armv8.4-a',
> >      },
> >      '0xd49': {
> > -        'march': 'armv8.5-a',
> > +        'march': 'armv9-a',
> >          'march_features': ['sve2'],
> >          'compiler_options': ['-mcpu=neoverse-n2'],
> >          'flags': [
> > @@ -630,7 +630,7 @@ if update_flags
> >      # probe supported archs and their features
> >      candidate_march = ''
> >      if part_number_config.has_key('march')
> > -        supported_marchs = ['armv8.6-a', 'armv8.5-a', 'armv8.4-a', 'armv8.3-a',
> > +        supported_marchs = ['armv9-a', 'armv8.6-a', 'armv8.5-a',
> 
> march may fallback to armv8.6-a if compiler doesn't support armv9-a. Is this
> fallback safe?

Yeah, looks like we need to have a fallback arch if compiler doesn't support a given march
Armv8.5-a in this case.

> I think just remove march from N2 part_number_config is OK.

I will remove the march from part number config for now.
But we should work on defining a fallback arch in future as there will always be a compiler support mismatch.

> 
> > + 'armv8.4-a', 'armv8.3-a',
> >                              'armv8.2-a', 'armv8.1-a', 'armv8-a']
> >          check_compiler_support = false
> >          foreach supported_march: supported_marchs
> > --
> > 2.25.1