xtensa: implement ccount calibration for s6000

Calculate core frequency from timers at boot time
instead of assuming a fixed frequency. This is
useful as the true frequency is set up by the
boot loader, thus variable.

Signed-off-by: Oskar Schirmer <os@emlix.com>
Signed-off-by: Chris Zankel <chris@zankel.net>
This commit is contained in:
Oskar Schirmer 2009-05-11 15:43:36 +02:00 committed by Chris Zankel
parent d15f05eb8c
commit b070a03f64
3 changed files with 29 additions and 0 deletions

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@ -80,6 +80,7 @@ config XTENSA_VARIANT_S6000
bool "s6000 - Stretch software configurable processor"
select VARIANT_IRQ_SWITCH
select ARCH_REQUIRE_GPIOLIB
select XTENSA_CALIBRATE_CCOUNT
endchoice
config XTENSA_UNALIGNED_USER

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@ -1,3 +1,4 @@
# s6000 Makefile
obj-y += irq.o gpio.o
obj-$(CONFIG_XTENSA_CALIBRATE_CCOUNT) += delay.o

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@ -0,0 +1,27 @@
#include <asm/delay.h>
#include <asm/timex.h>
#include <asm/io.h>
#include <variant/hardware.h>
#define LOOPS 10
void platform_calibrate_ccount(void)
{
u32 uninitialized_var(a);
u32 uninitialized_var(u);
u32 b;
u32 tstamp = S6_REG_GREG1 + S6_GREG1_GLOBAL_TIMER;
int i = LOOPS+1;
do {
u32 t = u;
asm volatile(
"1: l32i %0, %2, 0 ;"
" beq %0, %1, 1b ;"
: "=&a"(u) : "a"(t), "a"(tstamp));
b = xtensa_get_ccount();
if (i == LOOPS)
a = b;
} while (--i >= 0);
b -= a;
nsec_per_ccount = (LOOPS * 10000) / b;
ccount_per_jiffy = b * (100000UL / (LOOPS * HZ));
}