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

[Peter Chen <hzpeterchen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Fri, Jan 15, 2016 at 10:11:06AM -0500, Alan Stern wrote:
> 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)?
> 

I don't think we need to have such node, even root hub needs something
from device tree, it can get them from controller's node.

-- 

Best Regards,
Peter Chen
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