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Date:	Thu, 10 Oct 2013 21:41:40 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Stanimir Varbanov <svarbanov@...sol.com>,
	Theodore Ts'o <tytso@....edu>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	linux-kernel@...r.kernel.org, Rob Landley <rob@...dley.net>,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 0/2] Add support for Qualcomm's PRNG

On Wed, Oct 09, 2013 at 08:07:35AM -0700, H. Peter Anvin wrote:

> consider the PowerPC random number generator[1]) and

[snip]

> [1] which has a known first-order bias which they "correct" for by
> XORing two datums together in a very simple data reduction step.

65 actually, not two.

> However, if their random source has bias it is extremely likely it also
> has nonzero correlations, which require stronger reductions.  It would

The correlations are essentially zero, by design, and experiment
confirms it.  Did you see my mail on the kvm list where I explained
how it works?

Paul.
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