On Fri, Apr 07, 2017 at 12:25:49PM +0200, Linus Walleij wrote: > On Thu, Apr 6, 2017 at 3:35 PM, Laxman Dewangan <ldewangan@xxxxxxxxxx> wrote: > > > Currently, the GPIO interface is said to Open Drain if it is Single > > Ended and active LOW. Similarly, it is said as Open Source if it is > > Single Ended and active HIGH. > > > > The active HIGH/LOW is used in the interface for setting the pin > > state to HIGH or LOW when enabling/disabling the interface. > > > > In Open Drain interface, pin is set to HIGH by putting pin in > > high impedance and LOW by driving to the LOW. > > > > In Open Source interface, pin is set to HIGH by driving pin to > > HIGH and set to LOW by putting pin in high impedance. > > > > With above, the Open Drain/Source is unrelated to the active LOW/HIGH > > in interface. There is interface where the enable/disable of interface > > is ether active LOW or HIGH but it is Open Drain type. > > > > Hence decouple the Open Drain with Single Ended + Active LOW and > > Open Source with Single Ended + Active HIGH. > > > > Adding different flag for the Open Drain/Open Source which is valid > > only when Single ended flag is enabled. > > > > Signed-off-by: Laxman Dewangan <ldewangan@xxxxxxxxxx> > > Patch applied. > > 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. 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
