Re: [Buildroot] [PATCH 1/1] board/pine64/pinecube: new board

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Giulio, Jan, All,

On 2022-08-14 13:56 +0200, Giulio Benetti spake thusly:
> On 14/08/22 11:22, Jan Havran wrote:
> >>>+++ b/configs/pinecube_defconfig
> >>>+BR2_ARM_FPU_NEON_VFPV4=y
> >>This ^^^ should be removed since NEON doesn't support complete FPU
> >>standard API, so it's better to keep the default for BR2_cortex_a7
> >I will fix everything and post V2, but one thing I do not understand much is
> >this one.
> Here there is a very good explanation on why not adding by default
> BR2_ARM_FPU_NEON_VFPV4:
> https://lists.buildroot.org/pipermail/buildroot/2022-January/634728.html

I even tink that, ultimately, we should just remove FPU options that
also enable NEON, like BR2_ARM_FPU_NEON_VFPV4, because they do not make
sense.

Using NEON for floating-point arithmetics should probably left to a
per-pacakge setting, where and when t makes sense for that package (e.g.
math-intensive packages that can cope with incorrect results (like
real-time audio stuff that favour an occasional glitch rather than a
packet loss).

[--SNIP--]
> But yes, if VFPV4 is supported then yes, it makes sense to enable it
> instead of keeping the default. So since this board is S3 based and
> it supports VFPV4 then you can enable:
> BR2_ARM_FPU_VFPV4
> 
> and same can go with H3 based boards I think.
> 
> @Yann, what do you think about enabling VFPV4 on boards with SoCs
> that support VFPV4? (not NEON/VFPV4 of course)

Usually, defconfigs are very limited, and what we guarantee is very
basic: a booting kernel with basic drivers, and busybox' login and
shell. That does not use much floating-point instructions, so that would
not benefit much from using a "better" FPU.

I previously rejected the big series that bulk-converted all defconfigs
in one go, because that was not tested on real hardware.

But for a defconfig that was actually tested against real hardware, I
think it is OK that it uses a "better" FPU. So, if the pinecube has a
VFPv4, BR2_ARM_FPU_VFPV4 or BR2_ARM_FPU_VFPV4_D16 is OK.

Also nte that BR2_ARM_FPU_VFPV4 will make use of all the 32 flaoting
point registers, i.e. the full range, while BR2_ARM_FPU_VFPV4_D16 will
only make use of 16 registers. Not all VFPv4 implementation have 32
registers, so carefully enable the appropriate one (_D16 is safe to use
in either case, though).

Regards,
Yann E. MORIN.

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