[PATCH] qi: initialize / canonical PMU state effects vs Qi init

Werner Almesberger werner at openmoko.org
Wed Jan 28 00:51:04 CET 2009

Andy Green wrote:
> The bootloader should only touch things needed to get the Linux image in
> the first place,

While making sure it does so without leaving the 100mA (well, 80mA)
envelope. That's why Qi has to control so many things already.

For the kernel, the story is a bit different - the 100mA envelope
only matters if we're being booted from Qi or (on GTA02) u-boot.
In all other cases, we can reasonably expect whatever came before
us to have taken care of establishing useful power.

However, the kernel is still concerned with not wasting power on
things it doesn't need.

> and fix any non-sane defaults from reset or powerup
> that couldn't be avoided (variant defaults in PMU for example).  It
> shouldn't do anything else.

But why base the correctness of your kernel on the assumption that so
much else is not doing anything you didn't expect it to do when you
can just set things to the correct values and be done with it ?

I mean, this is an obviously fragile design, its fragility has already
revealed itself in real bugs, and I'm quite sure that we'll find more
once we proceed looking into current consumption in GTA02.

Besides, Qi already does a fairly comprehensive initialization of
GPIOs and the PMU, so ...

> That's the same model we need in the kernel.

... perhaps we do agree after all ? :-)

- Werner

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