linux-kernel - Re: [PATCH v2 2/2] sparc64: Use lzcnt instruction for fls and _

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Date:   Wed, 27 Sep 2017 14:02:38 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sam@...nborg.org
Cc:     vijay.ac.kumar@...cle.com, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, babu.moger@...cle.com,
        rob.gardner@...cle.com
Subject: Re: [PATCH v2 2/2] sparc64: Use lzcnt instruction for fls and __fls

From: Sam Ravnborg <sam@...nborg.org>
Date: Wed, 27 Sep 2017 21:56:37 +0200

> Hi Vijay.
> 
> On Wed, Sep 27, 2017 at 01:25:26PM -0600, Vijay Kumar wrote:
>> For T4 and above, patch fls and __fls functions
>> at the boot time to use lzcnt instruction.
>> 
>> Signed-off-by: Vijay Kumar <vijay.ac.kumar@...cle.com>
>> Reviewed-by: Babu Moger <babu.moger@...cle.com>
>> ---
>>  arch/sparc/Makefile         |    1 +
>>  arch/sparc/kernel/head_64.S |    2 ++
>>  arch/sparc/lib/Makefile     |    3 +++
>>  arch/sparc/lib/NG4fls.S     |   30 ++++++++++++++++++++++++++++++
>>  arch/sparc/lib/NG4patch.S   |    9 +++++++++
>>  5 files changed, 45 insertions(+), 0 deletions(-)
>> 
>> diff --git a/arch/sparc/Makefile b/arch/sparc/Makefile
>> index 8496a07..0763cd8 100644
>> --- a/arch/sparc/Makefile
>> +++ b/arch/sparc/Makefile
>> @@ -48,6 +48,7 @@ KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare
>>  KBUILD_CFLAGS += -Wa,--undeclared-regs
>>  KBUILD_CFLAGS += $(call cc-option,-mtune=ultrasparc3)
>>  KBUILD_AFLAGS += -m64 -mcpu=ultrasparc -Wa,--undeclared-regs
>> +KBUILD_AFLAGS += -Wa,-Asparc4
> This change is not justified anywhere??

It also will likely break with older tools.