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From: Yann E. MORIN <yann.morin.1998@free.fr>
To: buildroot@buildroot.org
Subject: [Buildroot] [git commit] Revert "configs/olimex_a20_olinuxino_lime: use NEON+VFPv4 as FPU strategy"
Date: Mon, 15 Aug 2022 21:03:49 +0200	[thread overview]
Message-ID: <20220815185003.24773876B0@busybox.osuosl.org> (raw)

commit: https://git.buildroot.net/buildroot/commit/?id=d5c1e67d3adf4d5c32e94ad7eac7a940fb17f9f0
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/master

The gcc man page states that specifying Neon as part of the fpu setting
has no effect, unless the -funsafe-math-optimizations is also specified,
because Neon is not compliant with IEEE 754:
```
    If the selected floating-point hardware includes the NEON extension
    (e.g. -mfpu=neon), note that floating-point operations are not
    generated by GCC's auto-vectorization pass unless
    -funsafe-math-optimizations is also specified. This is because NEON
    hardware does not fully implement the IEEE 754 standard for
    floating-point arithmetic (in particular denormal values are treated
    as zero), so the use of NEON instructions may lead to a loss of
    precision.
```

-funsafe-math-optimizations must be explictly specified per package to
really use NEON as FPU, but it's something that is left to the user as
well as setting BR2_ARM_FPU_NEON_VFPV4. This way the default
BR2_ARM_FPU_VFPV4D16 is used as previously. So let's revert the
offending patch.

This reverts commit 115ee0521430d89db8be1a79457b0721ceafc484.

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
---
 configs/olimex_a20_olinuxino_lime_defconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/configs/olimex_a20_olinuxino_lime_defconfig b/configs/olimex_a20_olinuxino_lime_defconfig
index b2364ca59a..ba814b98b8 100644
--- a/configs/olimex_a20_olinuxino_lime_defconfig
+++ b/configs/olimex_a20_olinuxino_lime_defconfig
@@ -2,7 +2,6 @@
 BR2_arm=y
 BR2_cortex_a7=y
 BR2_ARM_EABIHF=y
-BR2_ARM_FPU_NEON_VFPV4=y
 
 # Linux headers same as kernel, a 5.15 LTS series
 BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_15=y
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                 reply	other threads:[~2022-08-15 19:05 UTC|newest]

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