Re: [dpdk-dev] [PATCH v5 2/4] build: add arm32 meson build flags

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Jul 6, 2020 at 1:59 PM Juraj Linkeš <juraj.linkes@pantheon.tech> wrote:
>
> Base the flags on config/defconfig_arm-armv7a-linuxapp-gcc.
> Omit driver flags which can be built on arm32.
>
> Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>

Hi Juraj,

Not strictly specific to this patch. Just to understand, How armv7
support has been used?
- Is it for Running arm32 program on arm64 machines?
- Is it for Native DPDK support from arm32. If so, What kind of PMD
supports native arm32 DPDK?

Or some other use case?

I would like to understand the arm32 use case, so we can review it at
that angle.

> ---
>  config/arm/meson.build | 135 ++++++++++++++++++++++-------------------
>  1 file changed, 74 insertions(+), 61 deletions(-)
>
> diff --git a/config/arm/meson.build b/config/arm/meson.build
> index 8728051d5..b02fc95d9 100644
> --- a/config/arm/meson.build
> +++ b/config/arm/meson.build
> @@ -34,6 +34,11 @@ flags_generic = [
>         ['RTE_MAX_LCORE', 256],
>         ['RTE_USE_C11_MEM_MODEL', true],
>         ['RTE_CACHE_LINE_SIZE', 128]]
> +flags_generic_arm32 = [
> +       ['RTE_MACHINE', '"armv7a"'],
> +       ['RTE_MAX_LCORE', 128],
> +       ['RTE_USE_C11_MEM_MODEL', false],
> +       ['RTE_CACHE_LINE_SIZE', 64]]
>  flags_arm = [
>         ['RTE_MACHINE', '"armv8a"'],
>         ['RTE_MAX_LCORE', 16],
> @@ -63,6 +68,10 @@ flags_armada = [
>         ['RTE_MAX_LCORE', 16]]
>
>  flags_default_extra = []
> +flags_default_arm32_extra = [
> +        ['RTE_ARCH_ARM_NEON_MEMCPY', false],
> +        ['RTE_ARCH_STRICT_ALIGN', true],
> +        ['RTE_EAL_NUMA_AWARE_HUGEPAGES', false]]
>  flags_n1sdp_extra = [
>         ['RTE_MACHINE', '"n1sdp"'],
>         ['RTE_MAX_NUMA_NODES', 1],
> @@ -99,6 +108,9 @@ machine_args_generic = [
>         ['0xd0b', ['-mcpu=cortex-a76']],
>         ['0xd0c', ['-march=armv8.2-a+crc+crypto', '-mcpu=neoverse-n1'], flags_n1sdp_extra]]
>
> +machine_args_generic_arm32 = [
> +        ['default_arm32', ['-march=armv7-a', '-mtune=cortex-a9', '-mfpu=neon'], flags_default_arm32_extra]]
> +
>  machine_args_cavium = [
>         ['default', ['-march=armv8-a+crc+crypto','-mcpu=thunderx']],
>         ['native', ['-march=native']],
> @@ -114,6 +126,7 @@ machine_args_emag = [
>
>  ## Arm implementer ID (ARM DDI 0487C.a, Section G7.2.106, Page G7-5321)
>  impl_generic = ['Generic armv8', flags_generic, machine_args_generic]
> +impl_generic_arm32 = ['Generic armv7', flags_generic_arm32, machine_args_generic_arm32]
>  impl_0x41 = ['Arm', flags_arm, machine_args_generic]
>  impl_0x42 = ['Broadcom', flags_generic, machine_args_generic]
>  impl_0x43 = ['Cavium', flags_cavium, machine_args_cavium]
> @@ -136,74 +149,74 @@ if not dpdk_conf.get('RTE_ARCH_64')
>         dpdk_conf.set('RTE_ARCH_ARMv7', 1)
>         # the minimum architecture supported, armv7-a, needs the following,
>         # mk/machine/armv7a/rte.vars.mk sets it too
> -       machine_args += '-mfpu=neon'
>  else
>         dpdk_conf.set('RTE_CACHE_LINE_SIZE', 128)
>         dpdk_conf.set('RTE_ARCH_ARM64', 1)
> +endif
>
> -       machine = []
> -       cmd_generic = ['generic', '', '', 'default', '']
> -       cmd_output = cmd_generic # Set generic by default
> -       machine_args = [] # Clear previous machine args
> -       if arm_force_default_march and not meson.is_cross_build()
> +machine = []
> +machine_args = [] # Clear previous machine args
> +cmd_generic = ['generic', '', '', 'default', '']
> +cmd_output = cmd_generic # Set generic by default
> +if arm_force_default_march and not meson.is_cross_build()
> +       machine = impl_generic
> +       impl_pn = 'default'
> +elif not meson.is_cross_build()
> +       # The script returns ['Implementer', 'Variant', 'Architecture',
> +       # 'Primary Part number', 'Revision']
> +       detect_vendor = find_program(join_paths(
> +                       meson.current_source_dir(), 'armv8_machine.py'))
> +       cmd = run_command(detect_vendor.path())
> +       if cmd.returncode() == 0
> +               cmd_output = cmd.stdout().to_lower().strip().split(' ')
> +       endif
> +       # Set to generic if variable is not found
> +       machine = get_variable('impl_' + cmd_output[0], ['generic'])
> +       if machine[0] == 'generic'
>                 machine = impl_generic
> -               impl_pn = 'default'
> -       elif not meson.is_cross_build()
> -               # The script returns ['Implementer', 'Variant', 'Architecture',
> -               # 'Primary Part number', 'Revision']
> -               detect_vendor = find_program(join_paths(
> -                               meson.current_source_dir(), 'armv8_machine.py'))
> -               cmd = run_command(detect_vendor.path())
> -               if cmd.returncode() == 0
> -                       cmd_output = cmd.stdout().to_lower().strip().split(' ')
> -               endif
> -               # Set to generic if variable is not found
> -               machine = get_variable('impl_' + cmd_output[0], ['generic'])
> -               if machine[0] == 'generic'
> -                       machine = impl_generic
> -                       cmd_output = cmd_generic
> -               endif
> -               impl_pn = cmd_output[3]
> -               if arm_force_native_march == true
> -                       impl_pn = 'native'
> -               endif
> -       else
> -               impl_id = meson.get_cross_property('implementor_id', 'generic')
> -               impl_pn = meson.get_cross_property('implementor_pn', 'default')
> -               machine = get_variable('impl_' + impl_id)
> +               cmd_output = cmd_generic
>         endif
> -
> -       # Apply Common Defaults. These settings may be overwritten by machine
> -       # settings later.
> -       foreach flag: flags_common_default
> -               if flag.length() > 0
> -                       dpdk_conf.set(flag[0], flag[1])
> -               endif
> -       endforeach
> -
> -       message('Implementer : ' + machine[0])
> -       foreach flag: machine[1]
> -               if flag.length() > 0
> -                       dpdk_conf.set(flag[0], flag[1])
> -               endif
> -       endforeach
> -
> -       foreach marg: machine[2]
> -               if marg[0] == impl_pn
> -                       foreach flag: marg[1]
> -                               if cc.has_argument(flag)
> -                                       machine_args += flag
> -                               endif
> -                       endforeach
> -                       # Apply any extra machine specific flags.
> -                       foreach flag: marg.get(2, flags_default_extra)
> -                               if flag.length() > 0
> -                                       dpdk_conf.set(flag[0], flag[1])
> -                               endif
> -                       endforeach
> -               endif
> -       endforeach
> +       impl_pn = cmd_output[3]
> +       if arm_force_native_march == true
> +               impl_pn = 'native'
> +       endif
> +else
> +       impl_id = meson.get_cross_property('implementor_id', 'generic')
> +       impl_pn = meson.get_cross_property('implementor_pn', 'default')
> +       machine = get_variable('impl_' + impl_id)
>  endif
> +
> +# Apply Common Defaults. These settings may be overwritten by machine
> +# settings later.
> +foreach flag: flags_common_default
> +       if flag.length() > 0
> +               dpdk_conf.set(flag[0], flag[1])
> +       endif
> +endforeach
> +
> +message('Implementer : ' + machine[0])
> +foreach flag: machine[1]
> +       if flag.length() > 0
> +               dpdk_conf.set(flag[0], flag[1])
> +       endif
> +endforeach
> +
> +foreach marg: machine[2]
> +       if marg[0] == impl_pn
> +               foreach flag: marg[1]
> +                       if cc.has_argument(flag)
> +                               machine_args += flag
> +                       endif
> +               endforeach
> +               # Apply any extra machine specific flags.
> +               foreach flag: marg.get(2, flags_default_extra)
> +                       if flag.length() > 0
> +                               dpdk_conf.set(flag[0], flag[1])
> +                                message('Setting flag: @0@: @1@'.format(flag[0], flag[1]))
> +                       endif
> +               endforeach
> +       endif
> +endforeach
>  message(machine_args)
>
>  if (cc.get_define('__ARM_NEON', args: machine_args) != '' or
> --
> 2.20.1
>