[coreboot] [PATCH] make AMD CAR disable a C function

Kevin O'Connor kevin at koconnor.net
Sun May 16 19:50:35 CEST 2010

On Sun, May 16, 2010 at 06:46:34PM +0200, Rudolf Marek wrote:
> Following patch reworks car_disable into C. Tested, works here. I compared
> also the GCC generated code and it looks all right. Please test on some
> multicore CPU.

The AMD disable_cache_as_ram can be C code, but the other
architectures can not.  It would be nice if there was a single calling
convention for this capability across architectures.

Maybe something like:

void __regparm(3) __noreturn disable_car(void (*func)(u32), u32 param, u32 esp);

which would call func(param) on the stack specified by 'esp'.  The
caller would then do something like:

void romstage(u32 bist) {
    disable_car(load_ramstage, bist, CONFIG_RAMTOP)

void load_ramstage(u32 bist) {

> I added the "memory" clobber to read_cr0 / write_cr0 function as it is in Linux
> Kernel. Seems that if this is missing, GCC is too smart and messes the order
> of reads/writes to CR0 (not tested if really a problem here, but be safe for
> future users of this function ;)

Good catch!


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