(the first in probably a number of questions related to digging around in embedded linux-related code -- i know there's an embedded-linux list, if that's a better forum, i'll move stuff there.) currently writing an intro to GPIO for my new EL course, and ran across this in doc file gpio.txt: "Platforms must declare GENERIC_GPIO support in their Kconfig (boolean true), and provide an <asm/gpio.h> file. Drivers that can't work without standard GPIO calls should have Kconfig entries which depend on GENERIC_GPIO. The GPIO calls are available, either as "real code" or as optimized-away stubs, when drivers use the include file: #include <linux/gpio.h>" hang on ... that explanation might have been true at one time, but consider this snippet from <linux/gpio.h>: ... snip ... #ifdef CONFIG_GENERIC_GPIO #ifdef CONFIG_ARCH_HAVE_CUSTOM_GPIO_H #include <asm/gpio.h> #else #include <asm-generic/gpio.h> ... snip ... the above clearly suggests that you need provide an <asm/gpio.h> only if you've explicitly selected that you have a custom gpio.h file, and that Kconfig directive is defined thusly in drivers/gpio/Kconfig: config ARCH_HAVE_CUSTOM_GPIO_H bool help Selecting this config option from the architecture Kconfig allows the architecture to provide a custom asm/gpio.h implementation overriding the default implementations. New uses of this are strongly discouraged. so, if i read this correctly, you *don't* need to supply your own <asm/gpio.h> except under exceptional circumstances which, these days, is strongly discouraged, does that sound right? further, there are numerous kernel source files that explicitly have: #include <asm/gpio.h> when it would *seem* that the cleaner approach would be to simply: #include <linux/gpio.h> and set the Kconfig variable ARCH_HAVE_CUSTOM_GPIO_H, no? it just seems that the Doc/gpio.txt file could stand a bit of tweaking to be brought up to date. rday