[Arm-netbook] [eoma68] power issues

[luke.leighton]

folks, as you saw a couple months back we have an issue with the
EOMA68-A20 CPU Card where [without authorisation] some changes were
made to the power distribution by the ODM. i still haven't worked out
if those changes were/are a blessing or a curse.

a reminder of the issue: they connected the ACIN *directly* to VBUS on
the USB-OTG input, removing the usual safety and detection features (a
SY6280 plus use of some GPIO) which allow programmable (or
AXP209-controlled at least) switching between USB-OTG power and 5V
input power.

i have this sneaking suspicion that the solution might actually be
staring me in the face, so wanted to run it by people, see what they
thought.  what i *believe* the solution is, is to simply move that
USB-OTG/5V detection circuitry (in this case a SY6280 plus use of some
GPIO) onto the I/O boards, and to effectively treat the EOMA68 5V
power "as if" it was a USB-OTG two-way power system.

so rather than have in the spec "you must provide 5V power", change
that to "you must imagine that the power circuits are identical to
what you'd normally have to do for USB-OTG".  which, because wits-tech
directly connected the bloody USB-OTG power to the ACIN by fusing the
pins together at the AXP209 is actually exactly how it is.

the advantage of this change (i say change, it's more like being
frog-marched unwillingly towards a solution...) is that if people
happen to accidentally plug in the CPU Card into a USB-OTG socket and
keep it powered up, then

a) the CPU Card will survive unplugging and can transition happily
from one chassis to another

b) as long as it doesn't draw too much current it would be possible to
power a portable device *from* the USB-OTG... or at least charge its
battery (if it has one)

c) i'm sure there's something else...

anyway i *think* it's a blessing - it would just have been nice to
have been consulted by the ODM, eh?

if anyone's got any other suggestions on how to manage USB-OTG power
switching it would be very helpful to hear them: i will put them into
the EOMA68 spec as implementation guidelines.

l.