[PATCH] powerpc: merge include/asm/cputable.h
Arnd Bergmann
arnd at arndb.de
Thu Sep 15 09:58:09 EST 2005
On Middeweken 14 September 2005 21:11, Kumar Gala wrote:
> I not sure I understand what the introduction of the enum's gets us.
>
It doesn't have to be an enum, it could just as well be a #define,
if we find that to be better in some way (maybe compile-time).
The general idea is to convert run-time checks into compile-time
checks in order to improve the running kernel. If you have
// start code
enum {
FEATURE_1 = 1,
FEATURE_2 = 2,
PLATFORM_1 = FEATURE_1,
PLATFORM_2 = FEATURE_2,
PLATFORM_3 = FEATURE_1 | FEATURE_2,
FEATURE_POSSIBLE =
#ifdef CONFIG_PLATFORM_1
PLATFORM_1 |
#endif
#ifdef CONFIG_FEATURE_2
PLATFORM_2 |
#endif
#ifdef CONFIG_FEATURE_3
PLATFORM_3 |
#endif
0,
FEATURE_ALWAYS =
#ifdef CONFIG_PLATFORM_1
PLATFORM_1 &
#endif
#ifdef CONFIG_PLATFORM_2
PLATFORM_2 &
#endif
#ifdef CONFIG_PLATFORM_3
PLATFORM_3 &
#endif
FEATURE_POSSIBLE,
};
static inline int have_feature(unsigned long feature)
{
return (FEATURE_ALWAYS & feature) ||
(FEATURE_POSSIBLE & runtime_feature & feature);
}
int foo();
int bar();
int main(void)
{
if (have_feature(FEATURE_1))
return foo();
if (have_feature(FEATURE_2))
return bar();
return 0;
}
// end code
Then gcc will produce optimal object code for any combination
of CONFIG_PLATFORM_{1,2,3}. Of course I have to admit that the
header file is not exactly elegant ;-).
Arnd <><
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