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From: Peter Korsgaard <peter@korsgaard.com>
To: Giulio Benetti <giulio.benetti@benettiengineering.com>
Cc: Luca Ceresoli <luca.ceresoli@bootlin.com>,
	Jagan Teki <jagan@amarulasolutions.com>,
	"Yann E . MORIN" <yann.morin.1998@free.fr>,
	buildroot@buildroot.org
Subject: Re: [Buildroot] [PATCH 2/4] Revert "configs/olimex_a20_olinuxino_lime2: use NEON+VFPv4 as FPU strategy"
Date: Fri, 16 Sep 2022 23:46:51 +0200	[thread overview]
Message-ID: <874jx76lh0.fsf@dell.be.48ers.dk> (raw)
In-Reply-To: <20220815154854.17628-3-giulio.benetti@benettiengineering.com> (Giulio Benetti's message of "Mon, 15 Aug 2022 17:48:52 +0200")

>>>>> "Giulio" == Giulio Benetti <giulio.benetti@benettiengineering.com> writes:

 > 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 f8528acdfda278ea9f2f9bc8a47eb77ace0c050f.

 > Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>

Committed to 2022.05.x and 2022.02.x, thanks.

-- 
Bye, Peter Korsgaard
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  reply	other threads:[~2022-09-16 21:47 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-15 15:48 [Buildroot] [PATCH 0/4] Revert wrong NEON/VFPV4 FPU strategy Giulio Benetti
2022-08-15 15:48 ` [Buildroot] [PATCH 1/4] Revert "configs/olimex_a33_olinuxino: use NEON+VFPv4 as FPU strategy" Giulio Benetti
2022-08-16 20:46   ` Arnout Vandecappelle
2022-08-18 23:20     ` Giulio Benetti
2022-09-16 21:46   ` Peter Korsgaard
2022-08-15 15:48 ` [Buildroot] [PATCH 2/4] Revert "configs/olimex_a20_olinuxino_lime2: " Giulio Benetti
2022-09-16 21:46   ` Peter Korsgaard [this message]
2022-08-15 15:48 ` [Buildroot] [PATCH 3/4] Revert "configs/olimex_a20_olinuxino_lime: " Giulio Benetti
2022-09-16 21:46   ` Peter Korsgaard
2022-08-15 15:48 ` [Buildroot] [PATCH 4/4] Revert "configs/bananapi_m1: " Giulio Benetti
2022-09-16 21:47   ` Peter Korsgaard
2022-08-15 19:05 ` [Buildroot] [PATCH 0/4] Revert wrong NEON/VFPV4 FPU strategy Yann E. MORIN

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