From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [RFC/PATCH 0/3] Add devicetree scanning for randomness Date: Tue, 18 Feb 2014 11:19:27 -0700 Message-ID: <20140218181927.GE29304@obsidianresearch.com> References: <1392168805-14200-1-git-send-email-lauraa@codeaurora.org> <201402121251.06280.arnd@arndb.de> <20140212174554.GM27395@titan.lakedaemon.net> <20140212182000.GJ5554@obsidianresearch.com> <20140217155419.682F7C401D4@trevor.secretlab.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140217155419.682F7C401D4@trevor.secretlab.ca> Sender: linux-kernel-owner@vger.kernel.org To: Grant Likely Cc: Jason Cooper , Arnd Bergmann , keescook@chromium.org, devicetree@vger.kernel.org, Laura Abbott , linux-kernel@vger.kernel.org, Rob Herring , Kumar Gala , linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org On Mon, Feb 17, 2014 at 03:54:19PM +0000, Grant Likely wrote: > I applied a patch that did exactly that (109b623629), and then reverted > it (b920ecc82) shortly thereafter because add_device_randomness() is > a rather slow function and FDTs can get large. I'd like to see someone > do a reasonable analysis on the cost of using an FDT for randomness > before I reapply a patch doing something similar. An awful lot of the > FDT data is not very random, but there are certainly portions of it that > are appropriate for the random pool. I read through the original thread from Tim Bird and FWIW I agree with the assessment that passing the FDT through MD5 first is a good approach. Thinking into the future, I'd expect to see similar variable data in DT on servers as we see in DMI, including: - Vendor serial number for the HW, manufacturing date, model number, and HW UUID - Serial numbers and vendor part numbers for DIMMS - MAC addresses for all the ethernet - OEM specific data At worst a 'choosen/linux,no-dt-random = 1' value in the DT to disable it would solve the problem for those in embedded that care about microseconds during booting. Regards, Jason