(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
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