> -----Original Message----- > From: Juraj Linkeš <juraj.lin...@pantheon.tech> > Sent: Monday, January 22, 2024 9:59 PM > To: Pavan Nikhilesh Bhagavatula <pbhagavat...@marvell.com> > Cc: Jerin Jacob <jer...@marvell.com>; ruifeng.w...@arm.com; > n...@arm.com; Bruce Richardson <bruce.richard...@intel.com>; > dev@dpdk.org > Subject: Re: [EXT] Re: [PATCH 2/2] config/arm: add support for fallback march > > On Mon, Jan 22, 2024 at 1:16 PM Pavan Nikhilesh Bhagavatula > <pbhagavat...@marvell.com> wrote: > > > > > On Sun, Jan 21, 2024 at 10:37 AM <pbhagavat...@marvell.com> wrote: > > > > > > > > From: Pavan Nikhilesh <pbhagavat...@marvell.com> > > > > > > > > Some ARM CPUs have specific march requirements and > > > > are not compatible with the supported march list. > > > > Add fallback march in case the mcpu and the march > > > > advertised in the part_number_config are not supported > > > > by the compiler. > > > > > > > > > > It's not clear to me what this patch adds. We already have a fallback > > > mechanism and this basically does the same thing, but there's some > > > extra logic that's not clear to me. Looks like there are some extra > > > conditions around mcpu. In that case, all of the mcpu/march processing > > > should be done first and then we should do a common fallback. > > > > > > > The current fallback does a simple reverse compatibility check with the > compiler > > when force march is not enabled. > > But this is not true for neoverse-n2 case, as it is based on armv9-a which > > is a > super set of > > armv8.5-a and other features[1] > > In the current fallback path if both march neoverse-n2 and mcpu armv9-a > are not supported > > then it would fallback to armv8.6-a but this not correct as neoverse-n2 is > not based on armv8.5-a > > > > The fallback march armv8.5-a kicks in (if supported) when neoverse-n2 and > armv9-a are not supported. > > > > Can the two fallback mechanisms be combined? They seem very similar.
I will try to combine them in the next version. Thanks, Pavan. > > > > > [1] https://urldefense.proofpoint.com/v2/url?u=https- > 3A__github.com_gcc- > 2Dmirror_gcc_blob_615e25c82de97acc17ab438f88d6788cf7ffe1d6_gcc_confi > g_arm_arm-2Dcpus.in- > 23L306&d=DwIFaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=E3SgYMjtKCMVsB- > fmvgGV3o-g_fjLhk5Pupi9ijohpc&m=- > Xknjo5NapybFKTREn10YXl4HKVFwvwF7ZNL_2ks7_DxKC9Xynna3Ms2DLynVO > Fh&s=o_Pt0fUjpeoar7QSgqshIXDxOZVUSNQYcCtRJWhNS8I&e= > > > > > > > > Example > > > > mcpu = neoverse-n2 > > > > march = armv9-a > > > > fallback_march = armv8.5-a > > > > > > > > mcpu, march not supported > > > > machine_args = ['-march=armv8.5-a'] > > > > > > > > mcpu, march, fallback_march not supported > > > > least march supported = armv8-a > > > > > > > > machine_args = ['-march=armv8-a'] > > > > > > > > Signed-off-by: Pavan Nikhilesh <pbhagavat...@marvell.com> > > > > --- > > > > config/arm/meson.build | 15 +++++++++++++-- > > > > 1 file changed, 13 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/config/arm/meson.build b/config/arm/meson.build > > > > index 8c8cfccca0..2aaf78a81a 100644 > > > > --- a/config/arm/meson.build > > > > +++ b/config/arm/meson.build > > > > @@ -94,6 +94,7 @@ part_number_config_arm = { > > > > '0xd49': { > > > > 'march': 'armv9-a', > > > > 'march_features': ['sve2'], > > > > + 'fallback_march': 'armv8.5-a', > > > > 'mcpu': 'neoverse-n2', > > > > 'flags': [ > > > > ['RTE_MACHINE', '"neoverse-n2"'], > > > > @@ -709,14 +710,14 @@ if update_flags > > > > > > > > # probe supported archs and their features > > > > candidate_march = '' > > > > + supported_marchs = ['armv9-a', 'armv8.6-a', 'armv8.5-a', > > > > 'armv8.4-a', > > > > + 'armv8.3-a', 'armv8.2-a', 'armv8.1-a', > > > > 'armv8-a'] > > > > if part_number_config.has_key('march') > > > > if part_number_config.get('force_march', false) or support_mcpu > > > > if cc.has_argument('-march=' + > > > > part_number_config['march']) > > > > candidate_march = part_number_config['march'] > > > > endif > > > > else > > > > - supported_marchs = ['armv8.6-a', 'armv8.5-a', 'armv8.4-a', > 'armv8.3- > > > a', > > > > - 'armv8.2-a', 'armv8.1-a', 'armv8-a'] > > > > check_compiler_support = false > > > > foreach supported_march: supported_marchs > > > > if supported_march == part_number_config['march'] > > > > @@ -733,6 +734,16 @@ if update_flags > > > > endif > > > > > > > > if candidate_march != part_number_config['march'] > > > > + if part_number_config.has_key('fallback_march') and not > > > support_mcpu > > > > + fallback_march = part_number_config['fallback_march'] > > > > + foreach supported_march: supported_marchs > > > > + if (supported_march == fallback_march > > > > + and cc.has_argument('-march=' + > > > > supported_march)) > > > > + candidate_march = supported_march > > > > + break > > > > + endif > > > > + endforeach > > > > + endif > > > > warning('Configuration march version is @0@, not > > > > supported.' > > > > .format(part_number_config['march'])) > > > > if candidate_march != '' > > > > -- > > > > 2.25.1 > > > >
