Bug in split transactions on Raspberry Pi

[Alan Stern]

On Mon, 25 Jan 2016, Doug Anderson wrote:

> >> ...another interesting idea would be to try to see if you could just
> >> change the configuration of the Raspberry Pi kernel to switch which
> >> dwc2 driver it used.  Presumably their driver was an addition on top
> >> of the driver in "drivers/usb/dwc2".  In fact, doing a 'git log' on
> >> drivers/usb/dwc2 in the "rpi-4.4.y" kernel on github it looks pure
> >> (and Stefan is even the last commit author!)
> >
> > I'll try it.  In case it works: There have been lots of patches from
> > you and John posted to linux-usb in the last couple of months; which
> > ones should I apply for testing on top of d51c7d840b002?  (That was the
> > top commit on the master branch at the time I shallow-cloned the
> > Raspberry Pi kernel from github -- looks like it's based on 4.1.15.)
> 
> It's possible it makes more sense to switch to the 4.4 RPI kernel
> first to make thing simpler?  Presumably that would have fewer patches
> to try applying atop.

I installed the rpi-4.4.y branch from the 
https://github.com/raspberrypi/linux repository.  As is, it generated a 
working kernel.  Then I tried editing the config; I removed 
CONFIG_USB_DWCOTG and added CONFIG_USB_DWC2 and CONFIG_USB_DWC2_HOST.  
However, when I booted the resulting kernel it didn't seem to detect 
the host controller at all.  No USB devices were probed, which meant no 
working ethernet or keyboard.

Then I tried enabling both drivers in the config.  That worked, but the 
controller was bound to dwc_otg, not to dwc2.

I get the feeling that some magic DT incantation is missing, although I 
have no idea what.  The base bcm2709-rpi-2-b.dtb wasn't affected by the 
config change, nor was the overlays/dwc2-overlay.dtb file.

Any suggestions?

Alan Stern