Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759507AbXK0Svz (ORCPT ); Tue, 27 Nov 2007 13:51:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758771AbXK0SvQ (ORCPT ); Tue, 27 Nov 2007 13:51:16 -0500 Received: from mx1.redhat.com ([66.187.233.31]:33372 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758545AbXK0SvO (ORCPT ); Tue, 27 Nov 2007 13:51:14 -0500 Date: Tue, 27 Nov 2007 13:50:53 -0500 From: Dave Jones To: Udo van den Heuvel Cc: Andrew Morton , linux-kernel@vger.kernel.org, Michael Buesch , folkert van Heusden Subject: Re: enable dual rng on VIA C7 Message-ID: <20071127185053.GA30057@redhat.com> Mail-Followup-To: Dave Jones , Udo van den Heuvel , Andrew Morton , linux-kernel@vger.kernel.org, Michael Buesch , folkert van Heusden References: <47374EA4.1060009@xs4all.nl> <20071125233949.f64b2ecd.akpm@linux-foundation.org> <474AFC2F.1040309@xs4all.nl> <20071126185843.GD15764@redhat.com> <474C40FA.1070501@xs4all.nl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <474C40FA.1070501@xs4all.nl> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1534 Lines: 39 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? Dave -- http://www.codemonkey.org.uk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/