[U-Boot] [PATCH 4/4 v4] Preventing needless switching on and off PLL bypass mode, allowing allow single-stepping through the SPL

[Fabio Estevam]

Hi Marek,

On Tue, Feb 7, 2012 at 2:53 PM, Marek Vasut <marek.vasut at gmail.com> wrote:
>> From: Robert Delien <robert at delien.nl>
>>
>> This patch prevents the needless switching on and off of PLL bypass
>> mode. With this patch in place, single-stepping through the SPL is
>> now possible.
>
> Why did FSL have it in the bootlets though? Fabio, can you explain?

Anson (in Cc) explained the following:

"The switch of CPU clock is to make our EVK board can boot up the
uboot and kernel with less than 100mA power consumption to meet the
USB specification, because there is chance that the EVK board is power
by USB cable only, we need to make sure in this scenario, before USB
enum done, the total power consumption for our EVK board should be
less than 100mA, but if CPU running with PLL on, the power consumption
is > 100mA under uboot, so we need to disable PLL and switch CPU clock
to XTAL before USB enum done."

Regards,

Fabio Estevam