Documentation: CodingStyle: add inline assembly guidelines

work correctly.

		Chapter 19:  Inline assembly

In architecture-specific code, you may need to use inline assembly to interface

with CPU or platform functionality.  Don't hesitate to do so when necessary.

However, don't use inline assembly gratuitously when C can do the job.  You can

and should poke hardware from C when possible.

Consider writing simple helper functions that wrap common bits of inline

assembly, rather than repeatedly writing them with slight variations.  Remember

that inline assembly can use C parameters.

Large, non-trivial assembly functions should go in .S files, with corresponding

C prototypes defined in C header files.  The C prototypes for assembly

functions should use "asmlinkage".

You may need to mark your asm statement as volatile, to prevent GCC from

removing it if GCC doesn't notice any side effects.  You don't always need to

do so, though, and doing so unnecessarily can limit optimization.

When writing a single inline assembly statement containing multiple

instructions, put each instruction on a separate line in a separate quoted

string, and end each string except the last with \n\t to properly indent the

next instruction in the assembly output:

	asm ("magic %reg1, #42\n\t"

	     "more_magic %reg2, %reg3"

	     : /* outputs */ : /* inputs */ : /* clobbers */);

		Appendix I: References