On Wed, Jul 19, 2017 at 08:29:08PM +0530, Laxman Dewangan wrote: > >> Good that you found this and fixed it before someone git hurt. > > Well, while decoupling single-endedness from polarity was the right > > thing to do, this change did actually break the DT binary interface. > > > > If you have an old compiled dtb whose source used GPIO_OPEN_DRAIN, you > > now instead get *open-source* behaviour on 4.12: > > > > GPIO_OPEN_DRAIN = GPIO_SINGLE_ENDED | GPIO_ACTIVE_LOW > > > > => active-low, but *open source* > > > > while if you recompile that source against 4.12 you do get the expected > > open-drain behaviour, but now with inverted polarity: > > > > GPIO_OPEN_DRAIN = GPIO_SINGLE_ENDED | GPIO_LINE_OPEN_DRAIN > > > > => open drain, but *active high* > > > > requiring the device tree to be updated by specifying > > > > (GPIO_OPEN_DRAIN | GPIO_ACTIVE_LOW) > > > > I guess the latter is fine, even if it is likely to amount to a fair bit > > of debugging world wide. > > > > Perhaps all this can still be avoided by adding further flags and > > deprecating others before people start migrating to 4.12 (after all, > > GPIO_OPEN_DRAIN has been around since 4.4 even if there are no in-kernel > > users). > > > > Or we accept the binary interface breakage -- it probably is pretty rare > > that people update the kernel without updating the dtb. I can just > > update the dts on the system that broke for me, and hopefully anyone > > debugging this issue while updating to 4.12 will find this mail quickly. > > > > Yes, it breaks the older DTS with new kernel. However, this point was > discussed before sending patch. As there was no user in the mainline DTs > for these macros, we made change. These are generic gpio flags that can be used with a multitude of devices (e.g. regulators, reset-signals for all sorts of ICs, etc.), and whether there are any in-kernel users (dts) should probably not carry much weight. Some people are still stuck with 4.4 or 4.9 and it may still be a while before they update to, say, the next LTS kernel (4.13) and get bitten by this. Thanks, Johan -- 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
