From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <Tiejun.Chen@windriver.com>
Received: from mail1.windriver.com (mail1.windriver.com [147.11.146.13])
 (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits))
 (Client CN "mail1.windriver.com",
 Issuer "Intel External Basic Issuing CA 3A" (not verified))
 by ozlabs.org (Postfix) with ESMTPS id 4E09B2C007B
 for <linuxppc-dev@lists.ozlabs.org>; Fri,  7 Jun 2013 19:02:14 +1000 (EST)
Message-ID: <51B1A18A.6030002@windriver.com>
Date: Fri, 7 Jun 2013 17:02:02 +0800
From: "tiejun.chen" <tiejun.chen@windriver.com>
MIME-Version: 1.0
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: fsqrt
References: <1368679657.9603.32.camel@pasglop>
 <6A3DF150A5B70D4F9B66A25E3F7C888D0701C307@039-SN2MPN1-012.039d.mgd.msft.net>
 <3E027F8168735B46AC006B1D0C7BB0020B1E040F@039-SN2MPN1-011.039d.mgd.msft.net>
 <1368684547.9603.38.camel@pasglop> <51947A00.9010504@windriver.com>
 <1368685307.9603.39.camel@pasglop> <51947E35.30808@windriver.com>
 <1368686426.9603.49.camel@pasglop> <5194800D.3010606@windriver.com>
 <6A3DF150A5B70D4F9B66A25E3F7C888D0701C498@039-SN2MPN1-012.039d.mgd.msft.net>
 <1368687133.9603.51.camel@pasglop>
 <CAOZdJXU79kqEGk_nqv1NSzna7c=bgwSv+6WFgaTVjR4Rj4cZVg@mail.gmail.com>
 <1370577138.3766.342.camel@pasglop> <1370579976.3766.345.camel@pasglop>
 <3E027F8168735B46AC006B1D0C7BB0020B2135A0@039-SN2MPN1-012.039d.mgd.msft.net>
 <1370580426.3766.349.camel@pasglop>
 <3E027F8168735B46AC006B1D0C7BB0020B213817@039-SN2MPN1-012.039d.mgd.msft.net>
 <1370590884.3766.357.camel@pasglop> <51B18FD0.5040909@windriver.com>
 <1370595233.3766.360.camel@pasglop>
In-Reply-To: <1370595233.3766.360.camel@pasglop>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Cc: Xie Shaohui-B21989 <B21989@freescale.com>,
 Liu Qiang-B32616 <B32616@freescale.com>,
 Zang Roy-R61911 <r61911@freescale.com>, Timur Tabi <timur@tabi.org>,
 Fleming Andy-AFLEMING <afleming@freescale.com>,
 Bhushan Bharat-R65777 <R65777@freescale.com>,
 "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

On 06/07/2013 04:53 PM, Benjamin Herrenschmidt wrote:
> On Fri, 2013-06-07 at 15:46 +0800, tiejun.chen wrote:
>> On 06/07/2013 03:41 PM, Benjamin Herrenschmidt wrote:
>>> Another question...
>>>
>>> Do you guys happen to have a patch to emulate fsqrt in the kernel ?
>>
>> Seems this is already emulated:
>>
>> arch/powerpc/math-emu/fsqrt.c
>>
>> You can enable CONFIG_MATH_EMULATION to try.
>
> Is math emu expected to work at all on top of a real FPU ? I though it
> didn't ... maybe I'm wrong.

As I understand often the real FPU can't support all float instructions, so we 
have to enable this to emulate those unsupported float instructions in that 
scenario.

Tiejun