linux-kernel - Re: [PATCH] usb: udc: add gadget state kobject uevent

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Message-ID: <Pine.LNX.4.44L0.1307180946380.1245-100000@iolanthe.rowland.org>
Date:	Thu, 18 Jul 2013 09:50:37 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <balbi@...com>
cc:	Rong Wang <wr011235813@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <Rong.Wang@....com>
Subject: Re: [PATCH] usb: udc: add gadget state kobject uevent

On Thu, 18 Jul 2013, Felipe Balbi wrote:

> > > yes. Only the UDC driver knows when the controller is moving among those
> > > states.
> > 
> > Not quite.  Only the gadget driver knows when the transition between 
> > ADDRESS and CONFIGURED occurs.  This should be added to composite.c.
> 
> that's not entirely true :-) See how we handle that in dwc3:
> 
> | static int dwc3_ep0_set_config(struct dwc3 *dwc, struct usb_ctrlrequest *ctrl)
> | {
> | 	enum usb_device_state state = dwc->gadget.state;
> | 	u32 cfg;
> | 	int ret;
> | 	u32 reg;
> | 
> | 	dwc->start_config_issued = false;
> | 	cfg = le16_to_cpu(ctrl->wValue);
> | 
> | 	switch (state) {
> | 	case USB_STATE_DEFAULT:
> | 		return -EINVAL;
> | 		break;
> | 
> | 	case USB_STATE_ADDRESS:
> | 		ret = dwc3_ep0_delegate_req(dwc, ctrl);
> | 		/* if the cfg matches and the cfg is non zero */
> | 		if (cfg && (!ret || (ret == USB_GADGET_DELAYED_STATUS))) {
> | 			usb_gadget_set_state(&dwc->gadget,
> | 					USB_STATE_CONFIGURED);

In theory, this should not occur until the gadget driver has finished 
the transition to the CONFIGURED state, which doesn't occur until later 
in the case of USB_GADGET_DELAYED_STATUS.

> | 
> | 			/*
> | 			 * Enable transition to U1/U2 state when
> | 			 * nothing is pending from application.
> | 			 */
> | 			reg = dwc3_readl(dwc->regs, DWC3_DCTL);
> | 			reg |= (DWC3_DCTL_ACCEPTU1ENA | DWC3_DCTL_ACCEPTU2ENA);
> | 			dwc3_writel(dwc->regs, DWC3_DCTL, reg);
> | 
> | 			dwc->resize_fifos = true;
> | 			dev_dbg(dwc->dev, "resize fifos flag SET\n");
> | 		}
> | 		break;
> | 
> | 	case USB_STATE_CONFIGURED:
> | 		ret = dwc3_ep0_delegate_req(dwc, ctrl);
> | 		if (!cfg)
> | 			usb_gadget_set_state(&dwc->gadget,
> | 					USB_STATE_ADDRESS);

No check on the value of ret?  What if the request was rejected?

> | 		break;
> | 	default:
> | 		ret = -EINVAL;
> | 	}
> | 	return ret;
> | }

This illustrates the folly of exposing your code to public review.  :-)
Nevertheless, I take your point.

> Also, until other gadget drivers add notifications to the other cases, I
> don't think it's wise to add a transition from NOTATTACHED to
> CONFIGURED.

Another good point.

Alan Stern

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