Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751754AbdFTO7k (ORCPT ); Tue, 20 Jun 2017 10:59:40 -0400 Received: from mx2.suse.de ([195.135.220.15]:51644 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751116AbdFTO7i (ORCPT ); Tue, 20 Jun 2017 10:59:38 -0400 Date: Tue, 20 Jun 2017 16:59:33 +0200 From: Torsten Duwe To: Sean Wang Cc: Herbert Xu , mpm@selenic.com, robh+dt@kernel.org, mark.rutland@arm.com, clabbe.montjoie@gmail.com, prasannatsmkumar@gmail.com, romain.perier@free-electrons.com, shannon.nelson@oracle.com, weiyongjun1@huawei.com, devicetree@vger.kernel.org, linux-crypto@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, keyhaede@gmail.com Subject: Re: [PATCH v2 0/3] add support of hardware random generator on MediaTek MT7622 Message-ID: <20170620145933.GA4177@suse.de> References: <20170620034009.GD17764@gondor.apana.org.au> <1497968477.27946.5.camel@mtkswgap22> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1497968477.27946.5.camel@mtkswgap22> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 996 Lines: 28 On Tue, Jun 20, 2017 at 10:21:17PM +0800, Sean Wang wrote: > Hi Herbert, > > thanks for effort reviewing on those patches. > > By the way, also loop in Torsten > > Could you kindly guide me how to determine appropriate > rng->ops.quality value used by the driver? > > I have tested with rngtest on mtk-cir and the result is got as > the below log shown. If the rngtest always gives the result for > success rate over 99.8%, can I set the rng->ops.quality 998? > > rngtest: starting FIPS tests... > rngtest: bits received from input: 20000032 > rngtest: FIPS 140-2 successes: 998 > rngtest: FIPS 140-2 failures: 2 No! You'd have to determine the failure threshold of the test and apply some math to find a lower boundary of your RNG's entropy. What the quality is for: your RNG produces bits, but not all of them are completely independent of each other i.e. not completely random. So you simply lower the quality rating to express the net entropy contained in the data stream. Torsten