From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39076) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cvP5Q-0001dP-Fi for qemu-devel@nongnu.org; Tue, 04 Apr 2017 10:05:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cvP5P-00023Q-Ag for qemu-devel@nongnu.org; Tue, 04 Apr 2017 10:05:32 -0400 Received: from mail-wr0-x22d.google.com ([2a00:1450:400c:c0c::22d]:35279) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cvP5P-00022X-4G for qemu-devel@nongnu.org; Tue, 04 Apr 2017 10:05:31 -0400 Received: by mail-wr0-x22d.google.com with SMTP id k6so212043431wre.2 for ; Tue, 04 Apr 2017 07:05:31 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20170404134402.GA4196@kozik-book> References: <20170318192509.15499-1-krzk@kernel.org> <20170404134402.GA4196@kozik-book> From: Peter Maydell Date: Tue, 4 Apr 2017 15:05:09 +0100 Message-ID: Content-Type: text/plain; charset=UTF-8 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: Krzysztof Kozlowski Cc: Igor Mitsyanko , qemu-arm , QEMU Developers On 4 April 2017 at 14:44, Krzysztof Kozlowski wrote: > 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. :) The last RNG we added was hw/misc/bcm2835_rng.c, which uses qcrypto_random_bytes() to get cryptographically-random bytes from the host. On the other hand it sounds like this Exynos hardware is a PRNG without true-random input... > 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. That's rather odd. You're right that the datasheet is hopelessly uninformative about what's actually going on. thanks -- PMM