[PATCH 2/3] doc: dt-binding: generic onboard USB HUB
arnd at arndb.de
Wed Dec 9 00:55:43 PST 2015
On Wednesday 09 December 2015 16:12:24 Peter Chen wrote:
> On Tue, Dec 08, 2015 at 09:24:03PM -0600, Rob Herring wrote:
> > On Tue, Dec 08, 2015 at 10:58:48AM +0100, Arnd Bergmann wrote:
> > > On Tuesday 08 December 2015 10:50:49 Philipp Zabel wrote:
> > > > This something we don't have to define ad-hoc. The hub hangs off an USB
> > > > controller, right? The "Open Firmware recommended practice: USB"
> > > > document already describes how to represent USB devices in a generic
> > > > manner:
> > > > http://www.firmware.org/1275/bindings/usb/usb-1_0.ps
> > > >
> > > > Is there a reason not to reuse this?
> > > >
> > > > The usb hub node would be a child of the usb controller node, and it
> > > > could use
> > > > compatible = "usb,class9"; /* bDeviceClass 9 (Hub) */
> > >
> > > Good point, I had not thought of that when I looked at the patches.
> > >
> > > Yes, let's do this way. I don't know if we ever implemented the simple
> > > patch to associate a USB device with a device_node, but if not, then
> > > let's do it now for this driver. A lot of people have asked for it in
> > > the past.
> > Agreed. Also, some hubs have I2C buses as well, but I still think under
> > the USB bus is the right place.
> > However, one complication here is often (probably this case) these
> > addtional signals need to be controlled before the device enumerates.
> Yes, I did not find a way to let the USB bus code handle it, so I had to
> write a platform driver to do it
Looping in Ulf, he solved the same problem for SDIO devices recently,
and probably remembers the details best.
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