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>

3 files changed, 29 insertions, 0 deletions

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 30d21a9e2ef5..ebe228d02b08 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -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
diff --git a/arch/xtensa/variants/s6000/Makefile b/arch/xtensa/variants/s6000/Makefile
index 03b3975468bd..d83f3805130c 100644
--- a/arch/xtensa/variants/s6000/Makefile
+++ b/arch/xtensa/variants/s6000/Makefile
@@ -1,3 +1,4 @@
 # s6000 Makefile
 
 obj-y           += irq.o gpio.o
+obj-$(CONFIG_XTENSA_CALIBRATE_CCOUNT)   += delay.o
diff --git a/arch/xtensa/variants/s6000/delay.c b/arch/xtensa/variants/s6000/delay.c
new file mode 100644
index 000000000000..54b2b573f166
--- /dev/null
+++ b/arch/xtensa/variants/s6000/delay.c
@@ -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));
+}