Hello Surej,
> /*
> * Work out if we need multiple CPU support
> */
> #undef MULTI_CPU
> #undef CPU_NAME
>
> /*
> * CPU_NAME - the prefix for CPU related functions
> */
>
> # ifdef CONFIG_CPU_ARM7TDMI
> # ifdef CPU_NAME
> # undef MULTI_CPU
> # define MULTI_CPU
> # else
> # define CPU_NAME cpu_arm7tdmi
> # endif
> # endif
>
> In the beginning of the header file MULTI_CPU and CPU_NAME has been
> undefined. My question is if they have been undefined, what is the
> significance of the code #ifdef CPU_NAME?
The above looks weird to me as well.
> Also i would like to know
> the significance of __catify_fn.
>
> /*
> * Single CPU
> */
> #ifdef __STDC__
> #define __catify_fn(name,x) name##x
> #else
> #define __catify_fn(name,x) name/**/x
> #endif
> #define __cpu_fn(name,x) __catify_fn(name,x)
This is a simple jugglery such that __catify_fn always results in concatenation
of name & x (whether the compiler supports standard C preprocessor
concatenation or not).
>
> /*
> * If we are supporting multiple CPUs, then we must use a table of
> * function pointers for this lot. Otherwise, we can optimise the
> * table away.
> */
> #define cpu_proc_init __cpu_fn(CPU_NAME,_proc_init)
>
If you look closely, in case of a single CPU machine, cpu_proc_init is a
preprocessor will expand directly to that processor's init function. But in
case of multiprocessor machine, it will expand like this:
#define cpu_proc_init() processor._proc_init()
The variable "processor" is initialized like this (arch/arm26/kernel/setup.c:
setup_processor()):
for (list = &__proc_info_begin; list < &__proc_info_end ; list++)
if ((processor_id & list->cpu_mask) == list->cpu_val)
break;
/*
* If processor type is unrecognised, then we
* can do nothing...
*/
if (list >= &__proc_info_end) {
printk("CPU configuration botched (ID %08x), unable "
"to continue.\n", processor_id);
while (1);
}
processor = *list->proc;
The variables __proc_info_begin & __proc_info_end would be defined in linker
script.
Thanks,
Rajat
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