[U-Boot] [PATCH 08/24] armv8: add simple sdelay implementation

[Siarhei Siamashka <siarhei.siamashka@gmail.com>]

On Sun, 20 Nov 2016 14:57:02 +0000
Andre Przywara <andre.przywara@arm.com> wrote:

> The sunxi DRAM setup code needs an sdelay() implementation, which
> wasn't defined for armv8 so far.
> Shamelessly copy the armv7 version and adjust it to work in AArch64.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  arch/arm/cpu/armv8/cpu.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm/cpu/armv8/cpu.c b/arch/arm/cpu/armv8/cpu.c
> index e06c3cc..e82e9cf 100644
> --- a/arch/arm/cpu/armv8/cpu.c
> +++ b/arch/arm/cpu/armv8/cpu.c
> @@ -16,6 +16,19 @@
>  #include <asm/system.h>
>  #include <linux/compiler.h>
>  
> +/************************************************************
> + * sdelay() - simple spin loop.  Will be constant time as
> + *  its generally used in bypass conditions only.  This
> + *  is necessary until timers are accessible.
> + *
> + *  not inline to increase chances its in cache when called
> + *************************************************************/
> +void sdelay(unsigned long loops)
> +{
> +	__asm__ volatile ("1:\n" "subs %0, %1, #1\n"
> +			  "b.ne 1b":"=r" (loops):"0"(loops));

This inline assembly needs "cc" in the clobber list. Also don't we
want to just use a single register for the counter ("subs %0, %0, #1")
rather than trying to construct something excessively complicated
and possibly fragile?

The https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html page provides
some information.

> +}
> +
>  int cleanup_before_linux(void)
>  {
>  	/*


-- 
Best regards,
Siarhei Siamashka