With the previous implementation, rebooting without registering a recognized
reboot mode would end up with U-Boot checking for a valid power-on reason, which
might result in the device turning off (e.g. with no USB cable attached and no
buttons pressed).

Since this approach is not viable (breaks reboot in most cases), the validity of
the reboot reason is checked (in turn, by checking that a warm reset happened,
as there is no magic) to detect a reboot and the 'o' char is recognized to
indicate that power-off is required. Still, that might be overridden by the
detection of usual power-on reasons, on purpose.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

Reboot mode garbage is found on cold reset and might be seen as valid on the
next warm reset, thus it has to be cleared on cold reset.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

Some power on reasons are not desirable (e.g. too short press on the power
button), battery plug. Thus, power off the device when one of those occurs.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

USB ID pin pull-up indicates factory (fastboot) cable detection.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

This adds support for the omap4 reboot mode mechanism and exports the reboot
mode via an environment variable, that is used in the boot command to make it
possible to boot from the recovery partition or fastboot.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

This adds support for the MUSB USB dual-role controller in peripheral mode,
with configuration options for the fastboot USB gadget.

At this point, flashing the internal eMMC is support.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

The Amazon Kindle Fire (first generation) codename kc1 is a tablet that was
released by Amazon back in 2011.

It is using an OMAP4430 SoC GP version, which allows running U-Boot and the
U-Boot SPL from the ground up.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>