On Thu, Feb 11, 2016 at 11:00:48AM +0100, Maxime Ripard wrote: > 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... Evidently there is a communication failure. Generally, the statement has been that old DTBs should continue to work. That's even documented, as Andre pointed out: Documentation/devicetree/bindings/ABI.txt There are obviously shades of grey, and _rarely_ it might be necessary to deliberately break a binding. However, that should be the rare last-resort case, rather than a crutch for development. Saying "bad but ok" underplays the "bad" and overplays the "ok". > 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 is unfortunate that we cannot provide the level of review that we want to. Mistakes will happen even with review; that doesn't necessitate removing support for a binding. > > 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. I believe that in this case, Andre was complaining about this particular breakage, unless I have misunderstood. To be clear, I'm arguing for the strategy going forward. If no-one has complained about the stuff broken up to this point, let's not waste time restoring that. Going forward we need to keep old DTBs supported. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
