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

[André Przywara]

On 24/11/16 01:25, Siarhei Siamashka wrote:

Hi Siarhei,

> On Sun, 20 Nov 2016 14:57:02 +0000
> Andre Przywara <andre.przywara at 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 at 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?

Please don't shoot the messenger, this is the version copied from ARMv7.
I noticed the redundant register as well, but didn't dare to touch it
(assuming some higher wisdom behind it).
And good catch for the cc clobber!

Cheers,
Andre.

> The https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html page provides
> some information.
> 
>> +}
>> +
>>  int cleanup_before_linux(void)
>>  {
>>  	/*
> 
>