Re: [dpdk-dev] [PATCH v4 1/2] config/arm: select most suitable -march for kunpeng soc

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>
> 
> On Thu, May 13, 2021 at 6:41 PM Chengwen Feng
> <fengchengwen@huawei.com> wrote:
> >
> > Currently, the soc_kunpeng930 declares '-march=armv8.2-a+crypto+sve',
> > but some compiler doesn't recognize the march because it doesn't
> > support sve.
> >
> > To solve this bug we use the following scheme:
> > 1. Define 'march_base' tuple which defines support march, it should
> > arrange from lower to higher.
> > e.g. 'march_base' : ['-march=armv8-a', '-march=armv8.2-a'] 2. Define
> > 'march_feature' tuple which defines support feature.
> > e.g. 'march_feature' : ['crypto', 'sve'] 3. Select the most suitable
> > march+feature combination based on 'march_base' and 'march_feature'
> > tuples.
> > 4. Use the selected march+feature combination as the default
> > machine_args.
> >
> > Fixes: 7cf32a22b240 ("config/arm: add Hisilicon kunpeng")
> >
> > Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> > ---
> >  config/arm/meson.build | 27 +++++++++++++++++++++++++--
> >  1 file changed, 25 insertions(+), 2 deletions(-)
> >
> > diff --git a/config/arm/meson.build b/config/arm/meson.build index
> > 3f34ec9..8551a80 100644
> > --- a/config/arm/meson.build
> > +++ b/config/arm/meson.build
> > @@ -149,7 +149,9 @@ implementer_hisilicon = {
> >      ],
> >      'part_number_config': {
> >          '0xd01': {
> > -            'machine_args': ['-march=armv8.2-a+crypto', '-mtune=tsv110'],
> > +            'march_base' : ['-march=armv8-a', '-march=armv8.2-a'],
If the compiler supports armv8.1-a, you need to choose armv8.1-a.

> 
> Another target has the same issue. Could you fix that all together as it is
> generic problem in the existing infrastructure.
I think this needs to be more generic solution. IMO, the requirement is as follows:

1) We need to pick the most closest march_base supported by the compiler. For ex: If the SoC support v8.2 and the compiler supports v8.1, we need to pick v8.1
2) SoCs are allowed to support a base march version + hand picked features from the next 1 base marchs. i.e. armv8.x compliant implementation can include any features from armv8.(x + 1). Please refer to  Arm-ARM section A2 for more details. So, it is possible that the compiler supports a base march and a bunch of optional features from the next version. We need to test all the features allowed by the architecture and pick the ones that are supported in the compiler.

> 
> 
> > +            'march_feature' : ['crypto'],
> > +            'machine_args': ['-mtune=tsv110'],
> >              'flags': [
> >                  ['RTE_MACHINE', '"Kunpeng 920"'],
> >                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -158,7 +160,9
> > @@ implementer_hisilicon = {
> >              ]
> >          },
> >          '0xd02': {
> > -            'machine_args': ['-march=armv8.2-a+crypto+sve'],
> > +            'march_base' : ['-march=armv8-a', '-march=armv8.2-a'],
> > +            'march_feature' : ['crypto', 'sve'],
> > +            'machine_args': [],
> >              'flags': [
> >                  ['RTE_MACHINE', '"Kunpeng 930"'],
> >                  ['RTE_ARM_FEATURE_ATOMICS', true], @@ -449,8 +453,27
> > @@ else
> >      # add/overwrite flags in the proper order
> >      dpdk_flags = flags_common + implementer_config['flags'] +
> > part_number_config.get('flags', []) + soc_flags
> >
> > +    # select the most suitable march+feature combination
> > +    machine_march = []
> > +    if part_number_config.has_key('march_base')
> > +        foreach arch: part_number_config['march_base']
> > +            if cc.has_argument(arch)
> > +                machine_march = arch # Set the higher supported arch as
> possible
> > +            endif
> > +        endforeach
> > +    endif
> > +    if part_number_config.has_key('march_feature')
> > +        foreach feature: part_number_config['march_feature']
> > +            tmp_machine_march = machine_march + '+' + feature
> > +            if cc.has_argument(tmp_machine_march)
> > +                machine_march = tmp_machine_march # Set the more supported
> feature as possible
> > +            endif
> > +        endforeach
> > +    endif
> > +
> >      # apply supported machine args
> >      machine_args = [] # Clear previous machine args
> > +    machine_args += machine_march
> >      foreach flag: part_number_config['machine_args']
> >          if cc.has_argument(flag)
> >              machine_args += flag
> > --
> > 2.8.1
> >