[PATCH] icecube/lite5200b: document wakeup from low-power support

Signed-off-by: Domen Puncer <domen.puncer@telargo.com>

diff --git a/doc/README.Lite5200B_low_power b/doc/README.Lite5200B_low_power
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+Lite5200B wakeup from low-power mode (CONFIG_LITE5200B_PM)
+----------------------------------------------------------
+
+Low-power mode as described in Lite5200B User's Manual, means that
+with support of MC68HLC908QT1 microcontroller (refered to as QT),
+everything but the SDRAM can be powered down. This brings
+maximum power saving, while one can still restore previous state
+quickly.
+
+Quick overview where U-Boot comes into the picture:
+- OS saves device states
+- OS saves wakeup handler address to physical 0x0, puts SDRAM into
+  self-refresh and signals to QT, it should power down the board
+- / board is sleeping here /
+- someone presses SW4 (connected to QT)
+- U-Boot checks PSC2_4 pin, if QT drives it down, then we woke up,
+  so get SDRAM out of self-refresh and transfer control to OS
+  wakeup handler
+- OS restores device states
+
+This was tested on Linux with USB and Ethernet in use. Adding
+support for other devices is an OS issue.