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

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

On Fri, 15 Jan 2016, Arnd Bergmann wrote:

quoted

On Friday 15 January 2016 17:17:27 Peter Chen wrote:

quoted

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 <redacted>

Acked-by: Arnd Bergmann <redacted>


Just one last question:

quoted

 	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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