[Blackfin] arch: Functional power management support: Add support for cpu frequency scaling

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

1 files changed, 28 insertions, 2 deletions

diff --git a/arch/blackfin/kernel/time-ts.c b/arch/blackfin/kernel/time-ts.c
index 1ce8cb1e4982..4482c47c09e5 100644
--- a/arch/blackfin/kernel/time-ts.c
+++ b/arch/blackfin/kernel/time-ts.c
@@ -16,11 +16,35 @@
 #include <linux/irq.h>
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
+#include <linux/cpufreq.h>
 
 #include <asm/blackfin.h>
+#include <asm/time.h>
 
 #ifdef CONFIG_CYCLES_CLOCKSOURCE
 
+/* Accelerators for sched_clock()
+ * convert from cycles(64bits) => nanoseconds (64bits)
+ *  basic equation:
+ *              ns = cycles / (freq / ns_per_sec)
+ *              ns = cycles * (ns_per_sec / freq)
+ *              ns = cycles * (10^9 / (cpu_khz * 10^3))
+ *              ns = cycles * (10^6 / cpu_khz)
+ *
+ *      Then we use scaling math (suggested by george@mvista.com) to get:
+ *              ns = cycles * (10^6 * SC / cpu_khz) / SC
+ *              ns = cycles * cyc2ns_scale / SC
+ *
+ *      And since SC is a constant power of two, we can convert the div
+ *  into a shift.
+ *
+ *  We can use khz divisor instead of mhz to keep a better precision, since
+ *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ *  (mathieu.desnoyers@polymtl.ca)
+ *
+ *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ */
+
 static unsigned long cyc2ns_scale;
 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
 
@@ -82,8 +106,9 @@ static void bfin_timer_set_mode(enum clock_event_mode mode,
 {
         switch (mode) {
         case CLOCK_EVT_MODE_PERIODIC: {
-                unsigned long tcount = ((get_cclk() / (HZ * 1)) - 1);
+                unsigned long tcount = ((get_cclk() / (HZ * TIME_SCALE)) - 1);
                 bfin_write_TCNTL(TMPWR);
+                bfin_write_TSCALE(TIME_SCALE - 1);
                 CSYNC();
                 bfin_write_TPERIOD(tcount);
                 bfin_write_TCOUNT(tcount);
@@ -92,6 +117,7 @@ static void bfin_timer_set_mode(enum clock_event_mode mode,
                 break;
         }
         case CLOCK_EVT_MODE_ONESHOT:
+                bfin_write_TSCALE(0);
                 bfin_write_TCOUNT(0);
                 bfin_write_TCNTL(TMPWR | TMREN);
                 CSYNC();
@@ -115,7 +141,7 @@ static void __init bfin_timer_init(void)
         /*
          * the TSCALE prescaler counter.
          */
-        bfin_write_TSCALE(0);
+        bfin_write_TSCALE(TIME_SCALE - 1);
         bfin_write_TPERIOD(0);
         bfin_write_TCOUNT(0);