davinci: explain CLOCK_TICK_RATE of 27MHz in include/mach/timex.h

Leave a comment explaining the constant value of 27Mhz used
in include/mach/timex.h for all DaVinci platforms. Many of
the platforms actually run at 24MHz timer frequency (Eg.
EVMs of DM355, DM365 and OMAP-L1).

The comment also serves as a porting alert.
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>

arch/arm/mach-davinci/include/mach/timex.h

@@ -11,7 +11,12 @@
 #ifndef __ASM_ARCH_TIMEX_H
 #define __ASM_ARCH_TIMEX_H
 
-/* The source frequency for the timers is the 27MHz clock */
+/*
+ * Alert: Not all timers of the DaVinci family run at a frequency of 27MHz,
+ * but we should be fine as long as CLOCK_TICK_RATE or LATCH (see include/
+ * linux/jiffies.h) are not used directly in code. Currently none of the
+ * code relevant to DaVinci platform depends on these values directly.
+ */
 #define CLOCK_TICK_RATE 27000000
 
 #endif /* __ASM_ARCH_TIMEX_H__ */