On Mon, Apr 7, 2014 at 3:56 AM, Michael Heimpold <[email protected]> wrote: > Hi, > > I have a question regarding user-space gpio support with sysfs. > > Documentation/gpio/sysfs.txt states >> GPIO signals have paths like /sys/class/gpio/gpio42/ (for GPIO #42) >> and have the following read/write attributes: >> >> /sys/class/gpio/gpioN/ >> >> "direction" ... reads as either "in" or "out". This value may >> normally be written. ... >> >> Note that this attribute *will not exist* if the kernel >> doesn't support changing the direction of a GPIO, or >> it was exported by kernel code that didn't explicitly >> allow userspace to reconfigure this GPIO's direction. > > Imagine for example a generic user-space tool which enumerates > all available GPIOs to the user and sorts by input and output GPIOs. > How would such a tool classify an exported GPIO when kernel > doesn't export the 'direction' file via sysfs? Or in other words: how > can userspace detect the state (in vs. out) of a GPIO when 'direction' > is not exported?
Wouldn't the "value" field be read-only for a "in" GPIO and read-write for an "out" one? Other than that, I also don't see any drawback to having "direction" always exported and made read-only if direction cannot be changed. Alex. -- To unsubscribe from this list: send the line "unsubscribe linux-gpio" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
