[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>

include/asm-blackfin/time.h

@@ -0,0 +1,36 @@
+/*
+ * asm-blackfin/time.h:
+ *
+ * Copyright 2004-2008 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2 or later.
+ */
+
+#ifndef _ASM_BLACKFIN_TIME_H
+#define _ASM_BLACKFIN_TIME_H
+
+/*
+ * The way that the Blackfin core timer works is:
+ *  - CCLK is divided by a programmable 8-bit pre-scaler (TSCALE)
+ *  - Every time TSCALE ticks, a 32bit is counted down (TCOUNT)
+ *
+ * If you take the fastest clock (1ns, or 1GHz to make the math work easier)
+ *    10ms is 10,000,000 clock ticks, which fits easy into a 32-bit counter
+ *    (32 bit counter is 4,294,967,296ns or 4.2 seconds) so, we don't need
+ *    to use TSCALE, and program it to zero (which is pass CCLK through).
+ *    If you feel like using it, try to keep HZ * TIMESCALE to some
+ *    value that divides easy (like power of 2).
+ */
+
+#ifndef CONFIG_CPU_FREQ
+#define TIME_SCALE 1
+#else
+/*
+ * Blackfin CPU frequency scaling supports max Core Clock 1, 1/2 and 1/4 .
+ * Whenever we change the Core Clock frequency changes we immediately
+ * adjust the Core Timer Presale Register. This way we don't lose time.
+ */
+#define TIME_SCALE 4
+#endif
+
+#endif