On Mon, 21 Nov 2016 16:52:47 +0100 Alexander Graf agraf@suse.de wrote:
On 20/11/2016 15:57, Andre Przywara 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
I don't think it hurts to write this in C - and I also doubt that inlining has any negative effect.
Something along the lines of
static inline void sdelay(...) { for (; loops; loops--) asm volatile(""); }
inside a header should do the trick as well and is much more readable.
Unfortunately the performance of the generated C code is very unpredictable. Depending on the optimization settings, it may place the counter variable in a register, or keep it on stack.
It would be much nicer to have more predictable timings for these delays. So I like the assembly version a lot better. Naturally, when it is implemented correctly.
Alex
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));+}
int cleanup_before_linux(void) { /*