[U-Boot] [WIP, PATCH] initcall: An outline of the idea

[Laurence Withers]

Hi Graeme,

On Fri, Mar 02, 2012 at 10:05:12PM +1100, Graeme Russ wrote:
> diff --git a/doc/README.INIT_FUNC b/doc/README.INIT_FUNC
> new file mode 100644
> index 0000000..b545390
> --- /dev/null
> +++ b/doc/README.INIT_FUNC
> @@ -0,0 +1,31 @@
> +The INIT_FUNC macro allows initialisation functions (i.e. functions which are
> +executed before the main loop) to be easily added to the init sequence
> +
> +The format of the INIT_FUNC macro is:
> +
> +INIT_FUNC({function_name}, {init_class}, {prerequisite init_class(es)})
> +
> +{function_name} is the name of the init function to call. This function must
> +have the following prototype:
> +
> +int foo(void);
> +
> +Each init function must return 0 to indicate success - any other return value
> +indicates failure and the init sequence will stop
> +
> +{init_class} is a simple test string to describe the basic purpose of the init
> +function. Multiple init functions may share the same init_class string
> +
> +{prerequisite init_class(es)} is a list of init_class strings (see above) which
> +defines what init functions are executed before and after the given init
> +function. Each prerequisite init_class is seperated by a space and preceeded by
> +either:
> + * - At least one function of this init class must exist (i.e. there must be at
> +     least one INIT_FUNC entry with {init_class} set to the init class named
> +     after the '*' - All init functions with an init class matching the class
> +     named after the '*' will be executed before this function
> + + - All init functions with an init class matching the class named after the
> +     '+' will be executed before this function, but there does not need to be
> +     any functions with the named init class in the init sequence
> + - - This function will be called before any other functions with the init
> +     class named after the '-'

What happens if there's a set of dependencies that cannot be resolved? From
reading the above, it seems I can do something like this:

INIT_FUNC(ifunc1, class1, *class2);
INIT_FUNC(ifunc2, class2, *class1);

It would also seem that if you want to change the prerequisites for a given
init_class, you need to find every instance of INIT_FUNC for that init_class
and change it.

Perhaps there's a better way of solving this, but it maybe there should be a
separate place which names the init classes and their prerequisites?

> diff --git a/include/initcall.h b/include/initcall.h
> new file mode 100644
> index 0000000..a81cf21
> --- /dev/null
> +++ b/include/initcall.h
> @@ -0,0 +1,19 @@
> +#ifndef __INIT_CALL_H__
> +#define __INIT_CALL_H__
> +#include <linux/compiler.h>
> +#define INIT_FUNC(fn, init_name, deps) \
> +	static const char __init_func_ ## fn[] __used \
> +	__attribute__((__section__(".initfuncs"))) = \
> +	"(" #fn ":" #init_name ";" #deps ")\n";
> +
> +#define SKIP_INIT(init_name) \
> +	static const char __skip_init_ ## req[] __used \
> +	__attribute__((__section__(".initfuncs"))) = \
> +	"{" #init_name "}\n";
> +
> +#define REPLACE_INIT(old_func, new_func) \
> +	static const char __replace_init_ ## old_func[] __used \
> +	__attribute__((__section__(".initfuncs"))) = \
> +	"[" #old_func "," #new_func "]\n";
> +
> +#endif /* !__INIT_CALL_H__ */

What are SKIP_INIT() and REPLACE_INIT() used for?

Perhaps the macro could be expanded to include a prototype for the function,
so that gcc complains with a useful error message if there's a type mismatch.

Bye for now,
-- 
Laurence Withers, <lwithers at guralp.com>                http://www.guralp.com/
Direct tel:+447753988197 or tel:+443333408643               Software Engineer
General support queries: <support at guralp.com>         CMG-DCM CMG-EAM CMG-NAM