linux-kernel - Re: [PATCH] ARM: Use udiv/sdiv for __aeabi

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Message-ID: <527D32A9.2060603@codeaurora.org>
Date:	Fri, 08 Nov 2013 10:51:21 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
CC:	Rob Herring <robherring2@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

On 11/08/13 08:54, Russell King - ARM Linux wrote:
> On Fri, Nov 08, 2013 at 12:50:04PM +0100, Jean-Christophe PLAGNIOL-VILLARD wrote:
>> On 19:34 Thu 07 Nov     , Rob Herring wrote:
>>> On Thu, Nov 7, 2013 at 1:20 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>>>> If we're running on a v7 ARM CPU, detect if the CPU supports the
>>>> sdiv/udiv instructions and replace the signed and unsigned
>>>> division library functions with an sdiv/udiv instruction.
>>> [snip]
>>>
>>>> diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
>>>> index bd454b0..6ed6496 100644
>>>> --- a/arch/arm/lib/Makefile
>>>> +++ b/arch/arm/lib/Makefile
>>>> @@ -15,6 +15,9 @@ lib-y         := backtrace.o changebit.o csumipv6.o csumpartial.o   \
>>>>                    io-readsb.o io-writesb.o io-readsl.o io-writesl.o  \
>>>>                    call_with_stack.o
>>>>
>>>> +lib-$(CONFIG_CPU_V7) += div-v7.o
>>>> +CFLAGS_div-v7.o := -march=armv7-a
>>> Won't this fail to build if the compiler doesn't have armv7-a support.
>>> Perhaps we don't care about compilers that old.
>> use the propoer compiler to compile a armv7 kernel
> It's probably about time to get rid of the conditionals for this in
> the main arch/arm/Makefile actually - some of those date back some
> 10 or so years.  That's something for the v3.14 merge window.

I'll take that as an endorsement for not falling back to -march=armv5t
-Wa,-march=armv7-a like is done in arch/arm/Makefile.

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