linux-kernel - Re: enable dual rng on VIA C7

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Message-Id: <20071127125109.a2ef96f2.akpm@linux-foundation.org>
Date:	Tue, 27 Nov 2007 12:51:09 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>
Cc:	udovdh@...all.nl, linux-kernel@...r.kernel.org, mb@...sch.de,
	folkert@...heusden.com
Subject: Re: enable dual rng on VIA C7

On Tue, 27 Nov 2007 13:50:53 -0500
Dave Jones <davej@...hat.com> wrote:

> On Tue, Nov 27, 2007 at 05:08:26PM +0100, Udo van den Heuvel wrote:
>  > Dave Jones wrote:
>  > > On Mon, Nov 26, 2007 at 06:02:39PM +0100, Udo van den Heuvel wrote:
>  > > 
>  > >  > I did not know we are already that far ;-)
>  > >  > I mean: can this patch be aplied without hurting C3/C7 CPU's with just
>  > >  > one RNG? Maybe an expert needs to test/answer?
>  > >  > Maybe some logic needs to be applied around the extra bit?
>  > >  
>  > >>From the padlock spec..
>  > > 
>  > > "SRC Bits[9:8] Noise source select (I): These bits control the two noise
>  > >  sources on the processor that input bits to the accumulation buffers.
>  > >  On Nehemiah processors prior to stepping 8, these bits are reserved
>  > >  and undefined. The default RESET state is both bits = 0." 
>  > > 
>  > > Something like this perhaps ?
>  > 
>  > Yes, I think that's a big step in the right direction!
>  > 
>  > But I am no expert and cannot really judge how necessary or correct the
>  > implementation is w.r.t. the 'undefined' function bits for CPU's that
>  > lack a certain feature.
> 
> The checks at the end of the patch for the x86_mask/model ensure
> we only enable the 2nd noise source on CPUs documented to have it,
> so we should be safe.
> 
> Andrew, want to throw that in the -mm pile for a while?
> 

Did that, renamed to "via-rng: enable secondary noise source on CPUs where
it is present".

Has anyone tested it?
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