linux-kernel - Re: [PATCH 3/7] [RFC] add support for BlueGene/P FPU

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Date:	Thu, 19 May 2011 19:30:20 -0500
From:	Eric Van Hensbergen <ericvh@...il.com>
To:	Michael Neuling <mikey@...ling.org>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	bg-linux@...ts.anl-external.org
Subject: Re: [PATCH 3/7] [RFC] add support for BlueGene/P FPU

On Thu, May 19, 2011 at 6:16 PM, Michael Neuling <mikey@...ling.org> wrote:
> In message <BANLkTi=rc5vZm3xAXHpHSxSH1wBWKhv92A@...l.gmail.com> you wrote:
>> On Thu, May 19, 2011 at 4:36 PM, Michael Neuling <mikey@...ling.org> wrote:
>> > In message <BANLkTimKhApFW8G1-pG0u_9Kv2YB0R1O0w@...l.gmail.com> you wrote=
>> :
>> >> On Thu, May 19, 2011 at 12:58 AM, Michael Neuling <mikey@...ling.org> wr=
>> ote=3D
>> >> :
>> >> > Eric,
>> >> >
>> >> >> This patch adds save/restore register support for the BlueGene/P
>> >> >> double hummer FPU.
>> >> >
>> >> > What does this mean? =3DA0Needs more details here.
>> >> >
>>
>> okay, I've changed it a bit in [V2], if you want more I can do my best.
>
> If you can describe the whole primary and secondary registers that'd be
> cool.  ASCII art would be awesome! :-)
>

You sure you don't just want a bitfield.conf? :)  I'll do my best, but my
ASCII art isn't what it used to be.  I'll also include a reference to the PDF.

>> >
>> > Ok, sounds like there is 32*8*2 bytes of data, rather than the normal
>> > 32*8 bytes for FP only (ignoring VSX). =A0If this is the case, then you'l=
>> l
>> > need make 'fpr' in the thread struct bigger which you can do by setting
>> > TS_FPRWIDTH =3D 2 like we do for VSX.
>> >

Okay - so basically what I have now and TS_FPRWIDTH=2 ?

>>
>> Since it isn't available on other chips, shoudl it just be PPC_BGP_FPU
>> or PPC_BGP_DOUBLE_FPU?
>
> I'd probably still prefer it disassociated with the CPU name, but we are
> really bike shedding here.  I'm not too fussed.
>

I'll leave it separate and switch it to PPC_FP2 (or would you prefer
PPC_FP2_FPU to make it clear) since the public PDF refers to it this way.

If that all sounds good, I'll spin [V3] tomorrow.

     -eric
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