Re: [PATCH v3 3/3] Loongson-2F: Fixup of problems introduced by -mfix-loongson2f-jump of binutils 2.20.1

[Wu Zhangjin <wuzhangjin@gmail.com>]

On Wed, 2010-03-17 at 16:02 +0100, Ralf Baechle wrote:
> On Sat, Mar 13, 2010 at 12:34:17PM +0800, Wu Zhangjin wrote:
> 
> > -	/* reboot via jumping to boot base address */
> > +	/* reboot via jumping to boot base address
> > +	 *
> > +	 * ".set noat" and ".set at" are used to ensure the address not break
> > +	 * by the -mfix-loongson2f-jump option provided by binutils 2.20.1 (or
> > +	 * higher version) which try to change the jumping address to "addr &
> > +	 * 0xcfffffff" via the at($1) register, this is totally wrong for
> > +	 * 0xbfc00000 (LOONGSON_BOOT_BASE).
> > +	 */
> > +	__asm__ __volatile__(".set noat\n");
> >  	((void (*)(void))ioremap_nocache(LOONGSON_BOOT_BASE, 4)) ();
> > +	__asm__ __volatile__(".set at\n");
> 
> Ouch.  This is fragile and totally puts the kernels fate at the mercy of
> gcc and the ioremap_nocache() implementation.  GCC might emit a .set noat
> at any time.  Something like
> 
> void loongson_restart(char *command)
> {
> 	void (*func)(void);
> 
> 	/* do preparation for reboot */
> 	mach_prepare_reboot();
> 
> 	/* reboot via jumping to boot base address */
> 	func = (void *) ioremap_nocache(LOONGSON_BOOT_BASE, 4);
> 
> 	__asm__ __volatile__(
> 	"	.set	noat						\n"
> 	"	jr	%[func]						\n"
> 	"	.set	at						\n"
> 	: /* No outputs */
> 	: [func] "r" (func));
> }
> 
> should be safe against -mfix-loongson2f-jump I think.

Thanks very much, will apply it in the revision of this patch.

Regards,
	Wu Zhangjin