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SubjectRe: [PATCH 0/6] twl4030: Various fixes for charing-from-USB
On Thu, 10 May 2012, NeilBrown wrote:

> Maybe we need to not suspend the USB OTG interface when the device as a
> whole enters suspend-to-RAM. Maybe we need to register a dummy gadget to
> the bus active while in suspend?
> Does the gadget have to be responsive while-ever the bus is not suspended?

Yes.

> Maybe we can arrange for any USB activity to trigger a resume?

Probably not, at least, not fast enough. The gadget is required to
respond to USB packets within a few microseconds. At a minimum, the
USB device controller would have to remain fully powered.

> Entering suspend while still charging really should be possible - at least
> with a dump charger and hopefully from a host port as well. I'll like to
> find the best way to achieve that, and any help you can provide would be
> greatly appreciated.

If the gadget is attached to a dumb charger rather than a host then
there's no problem. But otherwise it's not so simple.

Have you read the USB charger class specification? (I haven't...)

Alan Stern



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