On Wed, Feb 10, 2016 at 04:30:01PM +0000, Mark Rutland wrote: > On Wed, Feb 10, 2016 at 03:37:55PM +0100, Maxime Ripard wrote: > > Hi Rob, > > > > On Wed, Feb 10, 2016 at 07:42:02AM -0600, Rob Herring wrote: > > > On Wed, Feb 10, 2016 at 6:30 AM, Andre Przywara <andre.przywara@xxxxxxx> wrote: > > > > Hi, > > > > > > > > just a ping: > > > > > > > > Are we really OK with breaking existing DTs in 4.6? (per the code in > > > > -next: f7d372ba54ea04d528a291b8dbe34716507bb60b, which is this patch). > > > > > > I only warn and make sure people are aware of the issue. I leave that > > > up to platform maintainers to decide. It depends on the maturity of > > > the platform and users. > > > > The impacted SoCs support is really partial. For the most supported > > one, big things like display or sound are totally missing, and we > > still update them on a regular basis to add support for new > > devices. As such, users are very likely to upgrade the DT from one > > version to another just because there's new devices available to > > them. And the newest SoC impacted just got introduced in 4.5, and only > > has the UART and MMC devices available. > > > > > If people complain about it then it's their mess. For platforms > > > supported in distros such as debian or fedora, I would strongly > > > recommend against breaking compatibility. > > > > None of them are officially supported: > > https://www.debian.org/releases/stable/armhf/ch02s01.html.en > > https://fedoraproject.org/wiki/Architectures/ARM#Fedora_23 > > > > Only the older one are, and they are not affected by this patch. > > > > > They do ship dtbs, but it's a chicken and egg problem. If dtbs were > > > stable and provided by firmware, then they wouldn't have to provide > > > them. If dtbs are unstable, then they have no choice. > > > > And while it might work great on platforms that have all the needed > > documentation, or a perfect one, which is our case. Almost each > > release, we discover that something is not working as it was > > documented, when it was documented in the first place. > > > > It also seems that even on well documented platforms, supported by the > > vendors, the stable ABI dream is not going to happen: > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/Atmel/README#n105 > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/arm/marvell,berlin.txt#n4 > > To be quite frank, I completely disagree with that stance. > > It seems like the only reason DT bindings aren't remaining stable is > because people are deliberately ignoring the requirement and reasoning > for doing so. And for DT maintainers saying on multiple occasions that it's bad but ok to break it and / or that they never actually said that it was a stable ABI... I'm guessing it could be a stable ABI if there was bindings reviews. Rob actually started to review a significant amount of bindings lately, and that's really appreciated, but if you don't review all the bindings, then we're going to make mistakes. > I agree that it can be painful, and that we cannot predict the future. > There will always be bugs. In our case, we can't even predict the present. > Having code in mainline comes with responsibilities. One of those is to > keep said code working for existing users. Otherwise, why bother having > it in mainline at all? None of our existing users ever complained. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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