linux-kernel - Re: Question about ARM FASTFPE

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Message-ID: <20190710082335.uzusesefimzpjd3f@shell.armlinux.org.uk>
Date:   Wed, 10 Jul 2019 09:23:35 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        masahiroy@...nel.org
Subject: Re: Question about ARM FASTFPE

On Wed, Jul 10, 2019 at 01:30:24PM +0900, Masahiro Yamada wrote:
> Hi.
> 
> I have a question about the following code
> in arch/arm/Makefile:
> 
> 
> # Do we have FASTFPE?
> FASTFPE :=arch/arm/fastfpe
> ifeq ($(FASTFPE),$(wildcard $(FASTFPE)))
> FASTFPE_OBJ :=$(FASTFPE)/
> endif
> 
> 
> Since arch/arm/fastfpe does not exist in the upstream tree,
> I guess this is a hook to compile downstream source code.
> 
> If a user puts arch/arm/fastfpe/ into their local source tree,
> Kbuild is supposed to compile the files in it.
> 
> Is this correct?
> 
> 
> If so, I am afraid this would not work for O= building.
> 
> $(wildcard ...) checks if this directory exists in the *objtree*,
> while scripts/Makefile.build needs to include
> arch/arm/fastfpe/Makefile from *srctree*.
> 
> I think the correct code should be like follows:
> 
> # Do we have FASTFPE?
> FASTFPE :=arch/arm/fastfpe
> ifneq ($(wildcard $(srctree)/$(FASTFPE)),)
> FASTFPE_OBJ :=$(FASTFPE)/
> endif
> 
> 
> Having said that, I am not sure this code is worth fixing.
> 
> This code was added around v2.5.1.9,

... as a _result_ of a discussion and deciding not to upstream it,
but to still allow its use.  Fastfpe is faster than nwfpe (so has
a definite advantage for FP intensive applications) but we decided
we didn't want two FP emulation codes in the kernel.  However, if
someone wants to use it, it has to be built into the kernel, it
can't be modular.

> and the actual source code for arch/arm/fastfpe/
> was never upstreamed.
> 
> 
> In general, we do not care much about the downstream code support.
> 
> What should we do about this?
> Fix and keep maintaining? Delete?
> 
> 
> -- 
> Best Regards
> Masahiro Yamada
> 

-- 
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