Re: [PATCH v3 1/1] USB: core: let USB device know device node

Alan Stern
2016-01-15T15:11:06Z

On Fri, 15 Jan 2016, Arnd Bergmann wrote:

> On Friday 15 January 2016 17:17:27 Peter Chen wrote:
> > Although most of USB devices are hot-plug's, there are still some devices
> > are hard wired on the board, eg, for HSIC and SSIC interface USB devices.
> > If these kinds of USB devices are multiple functions, and they can supply
> > other interfaces like i2c, gpios for other devices, we may need to
> > describe these at device tree.
> >
> > In this commit, it uses "reg" in dts as port number to match the port
> > number decided by USB core, if they are the same, then the device node
> > is for the device we are creating for USB core.
> >
> > Signed-off-by: Peter Chen <peter.chen-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
>
> Acked-by: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
>
>
> Just one last question:
>
> > dev->active_duration = -jiffies;
> > #endif
> > - if (root_hub) /* Root hub always ok [and always wired] */
> > + if (root_hub) { /* Root hub always ok [and always wired] */
> > dev->authorized = 1;
> > - else {
> > + dev->of_node = bus->controller->of_node;
>
>
> You are adding the of_node of the controller to the root hub, which I
> guess means that we now have two 'struct device' instances with the
> same of_node. They have different bus_types, so I think that is ok,
> but I wonder if it would be better to leave out the of_node for the
> root hub to avoid the confusion. Can you think of a case where we
> actually want to add properties for the root hub that we can't do
> more easily in the host controller?

There may not be any such cases, but there's still a good reason for
setting the root hub's of_node pointer: to initialize the recursion
along the USB device tree.

This leaves the question of whether OF will always use the same node to
represent the host controller and the root hub. In other words, if a
motherboard has a fixed device plugged into a fixed root-hub port, will
the DT description make that device a child of the host controller?
Or will there be a node in between (to represent the root hub)?

Alan Stern