Re: PXA27x UDC Power

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Thu, 29 Nov 2007, Justin Clacherty wrote:

> I've implemented this and it seems to work nicely (turning on the 
> charger anyway).  Now how do I go about reducing the draw back to 100 mA 
> when I'm disconnected so that I'm not still in 500 mA mode when USB is 
> plugged in again?

Do it in your gadget driver's disconect() method.  Just call
vbus_draw(100).  You need to know when disconnects occur anyway,
because your driver has to reinitialize itself.

> I was initially expecting that vbus_draw would be called with a mA value 
> of 100 or less when disconnecting but this doesn't seem to be the case.  
> I can't use vbus_session as we don't monitor vbus on our product.  Is 
> there some other function that's likely to be called on disconnect that 
> can be used to trigger a reduction in current draw?

IMO it's a bug if the controller driver doesn't reduce the current draw
back to 100 mA after a disconnect/reconnect cycle.  (It also is up to
the controller driver to reduce the draw during a USB suspend.)

This bug may be present in many of the drivers.  A little auditing 
would be in order.

Alan Stern


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