From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753844AbbIIHlb (ORCPT ); Wed, 9 Sep 2015 03:41:31 -0400 Received: from lists.s-osg.org ([54.187.51.154]:35067 "EHLO lists.s-osg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753499AbbIIHlO (ORCPT ); Wed, 9 Sep 2015 03:41:14 -0400 Subject: Re: [PATCH] ARM: exynos_defconfig: Enable USB Video Class support To: Krzysztof Kozlowski , linux-kernel@vger.kernel.org References: <1441662323-15468-1-git-send-email-javier@osg.samsung.com> <55EE9820.2010202@samsung.com> <55EE9F1A.9030703@osg.samsung.com> <55EEDECA.4040407@samsung.com> <55EEE370.9040705@osg.samsung.com> <55EF77EE.10301@samsung.com> Cc: Kukjin Kim , Thierry Reding , Anand Moon , Russell King , linux-samsung-soc@vger.kernel.org, Lukasz Majewski , linux-arm-kernel@lists.infradead.org, Bartlomiej Zolnierkiewicz From: Javier Martinez Canillas Message-ID: <55EFE293.8050400@osg.samsung.com> Date: Wed, 9 Sep 2015 09:41:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 MIME-Version: 1.0 In-Reply-To: <55EF77EE.10301@samsung.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Krzysztof, On 09/09/2015 02:06 AM, Krzysztof Kozlowski wrote: > On 08.09.2015 22:32, Javier Martinez Canillas wrote: > > (...) > >> >>> Let me rephrase my question into: >>> 1. What is worth enabling in exynos_defconfig? USB devices? I would >>> argue, except they are needed to boot. >> >> Ok, I understand your concern. The question is where we draw the line. >> >>> So maybe enable everything which Exynos boards have hard-wired? That >>> would make some sense... but we're making kernel larger. >>> >> >> In the case of this WebCam, it's not a typical USB device in the sense >> that is built in the Chromebook and not something that's plugged on an >> external USB port. > > Right, that is the difference from regular USB devices. > >> >>> 2. Maybe enable only what is a typical use case (including typical >>> testing cases)? Then we would have to define what "typical" means. For >>> example battery would be typical but camera would not. >>> >> >> There are a lot of board specific drivers that we currently enable as >> built-in like hwmon sensors or iio devices that are likely only present >> on a single board or a family of boards. >> >> So then I think all those drivers should be changed as a module as well, >> unless are critical for the board operation (i.e: thermal or fan drivers). > > Actually I think we should not judge by number of board using given > component but its usefulness in general exynos_defconfig case. Even when > something is used on just one board but it is important for that board, > then it should be built-in. > > For example hwmon monitoring stuff to get information about board > condition. Other example are leds on Odroid - to get visible condition > of the board. > > This don't have to be critical, but just important for testing. > > Additionally such components can be accessed usually from limited > user-space, e.g. system booted to console or SSH. > > If using a component requires more complex user-space (e.g. any kind of > window system), then probably already modules could be easily used. In > such cases I would expect the boot is not from network but from MMC and > there is a full-blown distro working. > Ok, fair enough. >>> 3. Argh, so maybe, if we agree that not everything is worth being >>> enabled, that additional stuff could be build as module? >>> >> >> Yes, I don't see anything wrong to enable more stuff as a module if >> that will give more build / test coverage. >> >> The goal of kernelci is to add functional tests so besides testing >> if a given kernel booted correctly, it's going to test if for example >> USB enumeration is working and has no regressions. For that use case >> is interesting to have support for the built-in USB devices like this >> camera (either as built-in or as a module). > > Okay, so we have some agreement that other stuff which is not important > but still hard-wired on Exynos boards (built into the board), can be > enabled as a module. So now we we have to draw the line which is > "important enough" to built-in and which is not so it could be as module. > >>>From my point of view media in general (cameras, tuners etc.) should be > put in the second category (module), especially that in usual to test > them you would have to boot system to a full graphical mode. Can you > test them from SSH connection? Maybe you could test DVB tuners by > reading status of packets but still output won't be visible. > Ok, my take on it was that if is wired into the board, then it should be supported out-of-the-box with a zImage build using exynos_defconfig but I see your point and looks reasonable to me. I'll wait a couple of days to see if others have more opinions and respin the patch with these options enabled as a module. Thanks a lot for your feedback! > Any comments from other interested parties? > > Best regards, > Krzysztof > Best regards, -- Javier Martinez Canillas Open Source Group Samsung Research America