From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7635C32754 for ; Mon, 5 Aug 2019 10:21:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 977B5214C6 for ; Mon, 5 Aug 2019 10:21:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728056AbfHEKV7 (ORCPT ); Mon, 5 Aug 2019 06:21:59 -0400 Received: from foss.arm.com ([217.140.110.172]:45428 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727158AbfHEKV6 (ORCPT ); Mon, 5 Aug 2019 06:21:58 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BB77728; Mon, 5 Aug 2019 03:21:57 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4A7183F694; Mon, 5 Aug 2019 03:21:56 -0700 (PDT) Subject: Re: [PATCH RFC] gpio: Add Virtual Aggregator GPIO Driver To: Linus Walleij , Geert Uytterhoeven , christoffer.dall@arm.com Cc: Bartosz Golaszewski , Alexander Graf , Peter Maydell , Paolo Bonzini , Magnus Damm , "open list:GPIO SUBSYSTEM" , QEMU Developers , Linux-Renesas , "linux-kernel@vger.kernel.org" References: <20190705160536.12047-1-geert+renesas@glider.be> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; prefer-encrypt=mutual; keydata= mQINBE6Jf0UBEADLCxpix34Ch3kQKA9SNlVQroj9aHAEzzl0+V8jrvT9a9GkK+FjBOIQz4KE g+3p+lqgJH4NfwPm9H5I5e3wa+Scz9wAqWLTT772Rqb6hf6kx0kKd0P2jGv79qXSmwru28vJ t9NNsmIhEYwS5eTfCbsZZDCnR31J6qxozsDHpCGLHlYym/VbC199Uq/pN5gH+5JHZyhyZiNW ozUCjMqC4eNW42nYVKZQfbj/k4W9xFfudFaFEhAf/Vb1r6F05eBP1uopuzNkAN7vqS8XcgQH qXI357YC4ToCbmqLue4HK9+2mtf7MTdHZYGZ939OfTlOGuxFW+bhtPQzsHiW7eNe0ew0+LaL 3wdNzT5abPBscqXWVGsZWCAzBmrZato+Pd2bSCDPLInZV0j+rjt7MWiSxEAEowue3IcZA++7 ifTDIscQdpeKT8hcL+9eHLgoSDH62SlubO/y8bB1hV8JjLW/jQpLnae0oz25h39ij4ijcp8N t5slf5DNRi1NLz5+iaaLg4gaM3ywVK2VEKdBTg+JTg3dfrb3DH7ctTQquyKun9IVY8AsxMc6 lxl4HxrpLX7HgF10685GG5fFla7R1RUnW5svgQhz6YVU33yJjk5lIIrrxKI/wLlhn066mtu1 DoD9TEAjwOmpa6ofV6rHeBPehUwMZEsLqlKfLsl0PpsJwov8TQARAQABtCNNYXJjIFp5bmdp ZXIgPG1hcmMuenluZ2llckBhcm0uY29tPokCTwQTAQIAOQIbAwYLCQgHAwIGFQgCCQoLBBYC AwECHgECF4AWIQSf1RxT4LVjGP2VnD0j0NC60T16QwUCXR3BUgAKCRAj0NC60T16Qyd/D/9s x0puxd3lI+jdLMEY8sTsNxw/+CZfyKaHtysasZlloLK7ftYhRUc63mMW2mrvgB1GEnXYIdj3 g6Qo4csoDuN+9EBmejh7SglM/h0evOtrY2V5QmZA/e/Pqfj0P3N/Eb5BiB3R4ptLtvKCTsqr 3womxCRqQY3IrMn1s2qfpmeNLUIfCUtgh8opzPtFuFJWVBzbzvhPEApZzMe9Vs1O2P8BQaay QXpbzHaKruthoLICRzS/3UCe0N/mBZQRKHrqhPwvjZdO0KMqjSsPqfukOJ8bl5jZxYk+G/3T 66Z4JUpZ7RkcrX7CvBfZqRo19WyWFfjGz79iVMJNIEkJvJBANbTSiWUC6IkP+zT/zWYzZPXx XRlrKWSBBqJrWQKZBwKOLsL62oQG7ARvpCG9rZ6hd5CLQtPI9dasgTwOIA1OW2mWzi20jDjD cGC9ifJiyWL8L/bgwyL3F/G0R1gxAfnRUknyzqfpLy5cSgwKCYrXOrRqgHoB+12HA/XQUG+k vKW8bbdVk5XZPc5ghdFIlza/pb1946SrIg1AsjaEMZqunh0G7oQhOWHKOd6fH0qg8NssMqQl jLfFiOlgEV2mnaz6XXQe/viXPwa4NCmdXqxeBDpJmrNMtbEbq+QUbgcwwle4Xx2/07ICkyZH +7RvbmZ/dM9cpzMAU53sLxSIVQT5lj23WLkCDQROiX9FARAAz/al0tgJaZ/eu0iI/xaPk3DK NIvr9SsKFe2hf3CVjxriHcRfoTfriycglUwtvKvhvB2Y8pQuWfLtP9Hx3H+YI5a78PO2tU1C JdY5Momd3/aJBuUFP5blbx6n+dLDepQhyQrAp2mVC3NIp4T48n4YxL4Og0MORytWNSeygISv Rordw7qDmEsa7wgFsLUIlhKmmV5VVv+wAOdYXdJ9S8n+XgrxSTgHj5f3QqkDtT0yG8NMLLmY kZpOwWoMumeqn/KppPY/uTIwbYTD56q1UirDDB5kDRL626qm63nF00ByyPY+6BXH22XD8smj f2eHw2szECG/lpD4knYjxROIctdC+gLRhz+Nlf8lEHmvjHgiErfgy/lOIf+AV9lvDF3bztjW M5oP2WGeR7VJfkxcXt4JPdyDIH6GBK7jbD7bFiXf6vMiFCrFeFo/bfa39veKUk7TRlnX13go gIZxqR6IvpkG0PxOu2RGJ7Aje/SjytQFa2NwNGCDe1bH89wm9mfDW3BuZF1o2+y+eVqkPZj0 mzfChEsiNIAY6KPDMVdInILYdTUAC5H26jj9CR4itBUcjE/tMll0n2wYRZ14Y/PM+UosfAhf YfN9t2096M9JebksnTbqp20keDMEBvc3KBkboEfoQLU08NDo7ncReitdLW2xICCnlkNIUQGS WlFVPcTQ2sMAEQEAAYkCHwQYAQIACQUCTol/RQIbDAAKCRAj0NC60T16QwsFD/9T4y30O0Wn MwIgcU8T2c2WwKbvmPbaU2LDqZebHdxQDemX65EZCv/NALmKdA22MVSbAaQeqsDD5KYbmCyC czilJ1i+tpZoJY5kJALHWWloI6Uyi2s1zAwlMktAZzgGMnI55Ifn0dAOK0p8oy7/KNGHNPwJ eHKzpHSRgysQ3S1t7VwU4mTFJtXQaBFMMXg8rItP5GdygrFB7yUbG6TnrXhpGkFBrQs9p+SK vCqRS3Gw+dquQ9QR+QGWciEBHwuSad5gu7QC9taN8kJQfup+nJL8VGtAKgGr1AgRx/a/V/QA ikDbt/0oIS/kxlIdcYJ01xuMrDXf1jFhmGZdocUoNJkgLb1iFAl5daV8MQOrqciG+6tnLeZK HY4xCBoigV7E8KwEE5yUfxBS0yRreNb+pjKtX6pSr1Z/dIo+td/sHfEHffaMUIRNvJlBeqaj BX7ZveskVFafmErkH7HC+7ErIaqoM4aOh/Z0qXbMEjFsWA5yVXvCoJWSHFImL9Bo6PbMGpI0 9eBrkNa1fd6RGcktrX6KNfGZ2POECmKGLTyDC8/kb180YpDJERN48S0QBa3Rvt06ozNgFgZF Wvu5Li5PpY/t/M7AAkLiVTtlhZnJWyEJrQi9O2nXTzlG1PeqGH2ahuRxn7txA5j5PHZEZdL1 Z46HaNmN2hZS/oJ69c1DI5Rcww== Organization: ARM Ltd Message-ID: Date: Mon, 5 Aug 2019 11:21:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On 01/08/2019 09:41, Linus Walleij wrote: > Hi Geert! > > Thanks for this very interesting patch! > > On Fri, Jul 5, 2019 at 6:05 PM Geert Uytterhoeven > wrote: > >> GPIO controllers are exported to userspace using /dev/gpiochip* >> character devices. Access control to these devices is provided by >> standard UNIX file system permissions, on an all-or-nothing basis: >> either a GPIO controller is accessible for a user, or it is not. >> Currently no mechanism exists to control access to individual GPIOs. > > Yes, I did that decision deliberately, as the chip is one device > and the base system control is usually on a per-device granularity. > At one point some people were asking for individual GPIO line > permissions in the character device and my argument was something > like why can't I have individual control over the access rights on a block > device or the pixels on a graphics device then. > > Jokes aside, filesystems do provide access control over individual > blocks on a block device in a way. So it is further up the stack. > > The same goes for this: something above the GPIO chip provide > more granular access control, and as such it fits the need very well. > >> Hence add a virtual GPIO driver to aggregate existing GPIOs (up to 32), >> and expose them as a new gpiochip. This is useful for implementing >> access control, and assigning a set of GPIOs to a specific user. >> Furthermore, it would simplify and harden exporting GPIOs to a virtual >> machine, as the VM can just grab the full virtual GPIO controller, and >> no longer needs to care about which GPIOs to grab and which not, >> reducing the attack surface. > > Excellent approach. > > I would even go so far as to call it "gpio-virtualization" or > "gpio-virtualized" rather than "gpio-virtual" so it is clear what the > intended usecase is. We have a bit of confusion in the kernel > because people misuse the word "virtual" left and right, like for > "virtual IRQ number" (Linux IRQ numbers) which are just some > random number space, but not really "virtual", it's a semantic > disease similar to the confusion of using the word "manual" in > computer code. I'd drop the notion of "virtual" altogether. Nothing is virtual in this thing at all (the GPIOs are very real, from what I gather). Instead (and assuming I got it right, which is a long shot), what you have is a "synthetic" GPIO controller, made from the GPIOs belonging to other controllers. I'd call it "GPIO aggregator". > > Here it is however used correctly! (Maybe for the first time.) > >> Virtual GPIO controllers are instantiated by writing to the "new_device" >> attribute file in sysfs: >> >> $ echo " [ ...]" >> "[, [ ...]] ...]" >> > /sys/bus/platform/drivers/gpio-virt-agg/new_device >> >> Likewise, virtual GPIO controllers can be destroyed after use: >> >> $ echo gpio-virt-agg. \ >> > /sys/bus/platform/drivers/gpio-virt-agg/delete_device > > I suppose this is the right way to use sysfs. > > I would check with some virtualization people (paged Marc Zyngier > and Christoffer Dall) so they can say whether this is the way any > virtual machine wants to populate its local GPIO chip for > use with a certain machine. > > If QEMU can deal in a simple and straight-forward way with this > I see it quickly becoming a very useful tool for industrial automation > where you want to run each control system in isolation and just > respawn the virtual machine if something goes wrong. What the VMM (QEMU, kvmtool) would need to do is to present this as a "standard" GPIO IP, and use the backend aggregator to emulate it. Certainly doable. The nice part is that all the work is in userspace, and thus completely off my plate! ;-) You also may want to look into not emulating a standard IP, but use something virtio-based instead. The ACRN project seems to have something like this in progress, but I know nothing about it. Thanks, M. -- Jazz is not dead. It just smells funny...