On Mon, Jan 19, 2015 at 07:52:17PM +0200, Roger Quadros wrote:

Hi,

On DRA7 EVMs the USB ID pin is connected to a GPIO line. The USB drivers
(dwc3 + dwc3-omap) depend on extcon framework to get the USB cable state
(USB or USB-Host) to put the controller in the right mode.

There were earlier attempts [1] to get this working by trying to patch up
the existing GPIO extcon driver.

This series attemts to take a different approach by introducing a new
USB specific extcon driver to handle the USB ID GPIO pin and
interpret a right USB cable state.

The reasoning to introduce this new driver is:
1) The existing GPIO extcon driver doesn't understand USB cable states
and it can't handle more than one cable per instance.
   
For the USB case we need to handle at least 2 cable states.
    a) USB (attach/detach)
    b) USB-Host (attach/detach)
and could possible include more states like
    c) Fast-charger (attach/detach)
    d) Slow-charger (attach/detach)
    
2) This USB specific driver can be easily updated in the future to
handle VBUS events, or charger detect events, in case it happens
to be available on GPIO for any platform.

3) The DT implementation is very easy. You just need one extcon node per USB
instead of one extcon node per cable state as in case of [1].

4) The cable state string doesn't need to be encoded in the device tree
as in case of [1].

5) With only ID event available, you can simulate a USB-peripheral attach
when USB-Host is detacted instead of hacking the USB driver to do the same.

Tested on DRA7-evm and DRA72-evm.

while at that, you might want to patch X15 too.

-- 
balbi