powerpc/mpc85xx: Add support for single source clocking

Single-source clocking is new feature introduced in T1040.
In this mode, a single differential clock is supplied to the
DIFF_SYSCLK_P/N inputs to the processor, which in turn is
used to supply clocks to the sysclock, ddrclock and usbclock.

So, both ddrclock and syclock are driven by same differential
sysclock in single-source clocking mode whereas in normal clocking
mode, generally separate DDRCLK and SYSCLK pins provides
reference clock for sysclock and ddrclock

DDR_REFCLK_SEL rcw bit is used to determine DDR clock source
-If DDR_REFCLK_SEL rcw bit is 0, then DDR PLLs are driven in
 normal clocking mode by DDR_Reference clock

-If DDR_REFCLK_SEL rcw bit is 1, then DDR PLLs are driven in
 single source clocking mode by DIFF_SYSCLK

Add code to determine ddrclock based on DDR_REFCLK_SEL rcw bit.

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/README b/README
index e58e9c0e1c..a0646c3665 100644
--- a/README
+++ b/README
@@ -423,6 +423,11 @@ The following options need to be configured:
 		CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULT
 		This value denotes start offset of DSP CCSR space.
 
+		CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
+		Single Source Clock is clocking mode present in some of FSL SoC's.
+		In this mode, a single differential clock is used to supply
+		clocks to the sysclock, ddrclock and usbclock.
+
 - Generic CPU options:
 		CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN