From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33337) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cvOl6-00038n-VW for qemu-devel@nongnu.org; Tue, 04 Apr 2017 09:44:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cvOl5-000830-U1 for qemu-devel@nongnu.org; Tue, 04 Apr 2017 09:44:33 -0400 Date: Tue, 4 Apr 2017 15:44:02 +0200 From: Krzysztof Kozlowski Message-ID: <20170404134402.GA4196@kozik-book> References: <20170318192509.15499-1-krzk@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH v2] hw/misc: Add Exynos4210 Pseudo Random Number Generator List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Igor Mitsyanko , qemu-arm , QEMU Developers On Tue, Apr 04, 2017 at 01:09:08PM +0100, Peter Maydell wrote: > On 18 March 2017 at 19:25, Krzysztof Kozlowski wrote: > > Add emulation for Exynos4210 Pseudo Random Number Generator which could > > work on fixed seeds or with seeds provided by True Random Number > > Generator block inside the SoC. > > > > Implement only the fixed seeds part of it in polling mode (no > > interrupts). Simple testing: > > # echo "exynos" > /sys/class/misc/hw_random/rng_current > > # dd if=/dev/hwrng of=/dev/null bs=1 count=16 > > > > Signed-off-by: Krzysztof Kozlowski > > > > --- > > > > Changes since v1: > > 1. Use GRand-like functions to fix build on MingW32 (this adds also > > finalize). > > 2. Add DPRINTF macro. > > 3. Use HWADDR_PRIx and family for printing values. > > Is there a data sheet that describes this RNG? I had a quick google > but couldn't find anything in the 4210 manual you can get from Samsung. Official and public datasheet - I never heard about it... AFAIK, Samsung never released any datasheet... But recently I found a copy of Exynos4412 datasheet published on FriendlyArm website: http://wiki.friendlyarm.com/wiki/index.php/NanoPC-T1 (at the bottom in "Resources"). Some blocks in Exynos4412, including the RNG, are the same as in Exynos4210. However, you should not expect too much data about the RNG in the datasheet... > In particular I'm not sure we want to use GRand here. Now, I am not sure neither. :) Let me describe the background: Recently I started also improving the Linux kernel driver for RNG module which ended in writing a new driver followed by discussions from which I learnt a lot. See [1][2][3] The datasheet is not saying too much how the RNG module works inside... so it is all a guessing. I must admit that I wrote the QEMU RNG part mostly looking at behavior of kernel driver and combining the knowledge with information obtained from datasheet. Thus I used GRand to have repeatable sequences for same seed. During the discussions about new kernel driver, I found that this RNG module (at least on Exynos4412 board) requires seeding but it is not following the Pseudo RNG behavior - seeding with the same value produces different results. This means that GRand would not be needed here. The new driver (not merged yet) took this into account and it behaves differently than previous one. Most notably it tries to be a better pseudo random number generator in terms of randomness. I did not test the new kernel driver with this QEMU RNG driver because it uses different user-space API and I still did not configure full Linux box in QEMU (mounting root, having some distro in the image). I am booting the QEMU kernel to initramfs with some toolset included. [1] https://www.spinics.net/lists/kernel/msg2474154.html [2] https://www.spinics.net/lists/arm-kernel/msg571653.html [3] https://www.spinics.net/lists/arm-kernel/msg571516.html Best regards, Krzysztof