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

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Message-ID: <474C40FA.1070501@xs4all.nl>
Date:	Tue, 27 Nov 2007 17:08:26 +0100
From:	Udo van den Heuvel <udovdh@...all.nl>
To:	Dave Jones <davej@...hat.com>,
	Udo van den Heuvel <udovdh@...all.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Michael Buesch <mb@...sch.de>,
	folkert van Heusden <folkert@...heusden.com>
Subject: Re: enable dual rng on VIA C7

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.
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