[U-Boot] Make "usb start" only start / scan usb once ?

[Hans de Goede <hdegoede@redhat.com>]

Hi,

Currently we've this magic in include/config_distro_bootcmd.h to avoid
scanning the usb bus multiple times.

And it does not work when also using an usb keyboard because then the
preboot command has already scanned the bus, so we're still scanning it
twice.

While discussing my latest attempt at fixing this:

http://patchwork.ozlabs.org/patch/413394/
http://patchwork.ozlabs.org/patch/413395/

With Ian, Ian said why not simply make "usb start" keep track of if it
already has started things, and then we can remove all the magic for it
from include/config_distro_bootcmd.h and just call it unconditionally.

This would also cause "usb start" and "usb reset" to actually do something
different, where as currently they are 100% the same.

I must say I like this idea, the only downside is, that it could be seen
as a break of the u-boot cmdline API, one could easily argue it is not,
because usb will be started by "usb start" if necessary, and people can
still force a rescan with "usb reset".

So any input on this, specifically would a patch-set to make "usb start"
start usb only once (per boot) be acceptable ?

Regards,

Hans