Switch the i.MX27's PLL in a safe manner

Changing PLL settings is somehow tricky on the i.MX27: Whenever the clock
speed of the main PLL is changed, the clock stops for about 100 us until the
PLL locks into the new frequency. While this clock stop, also the SDRAM
controller cannot refresh the memory, because it uses the same clock source.
This can lead into data loss and random system crashes.

This patch divides the PLL setting in two steps. First step is to re-program
the PLL and clock settings to values possible at a core supply of 1.25 V.
Second step is to increase the core power supply to 1.45 V and switch the
CPU clock to the specified 400 MHz.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

0 files changed, 0 insertions, 0 deletions