usb: chipidea: udc: workaround for endpoint conflict issue

BugLink: https://bugs.launchpad.net/bugs/1836668

commit c19dffc0 upstream.

An endpoint conflict occurs when the USB is working in device mode
during an isochronous communication. When the endpointA IN direction
is an isochronous IN endpoint, and the host sends an IN token to
endpointA on another device, then the OUT transaction may be missed
regardless the OUT endpoint number. Generally, this occurs when the
device is connected to the host through a hub and other devices are
connected to the same hub.

The affected OUT endpoint can be either control, bulk, isochronous, or
an interrupt endpoint. After the OUT endpoint is primed, if an IN token
to the same endpoint number on another device is received, then the OUT
endpoint may be unprimed (cannot be detected by software), which causes
this endpoint to no longer respond to the host OUT token, and thus, no
corresponding interrupt occurs.

There is no good workaround for this issue, the only thing the software
could do is numbering isochronous IN from the highest endpoint since we
have observed most of device number endpoint from the lowest.

Cc: <stable@vger.kernel.org> #v3.14+
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Jun Li <jun.li@nxp.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/usb/chipidea/udc.c

@@ -1614,6 +1614,25 @@ static int ci_udc_pullup(struct usb_gadget *_gadget, int is_on)
 static int ci_udc_start(struct usb_gadget *gadget,
 			 struct usb_gadget_driver *driver);
 static int ci_udc_stop(struct usb_gadget *gadget);
+
+/* Match ISOC IN from the highest endpoint */
+static struct usb_ep *ci_udc_match_ep(struct usb_gadget *gadget,
+			      struct usb_endpoint_descriptor *desc,
+			      struct usb_ss_ep_comp_descriptor *comp_desc)
+{
+	struct ci_hdrc *ci = container_of(gadget, struct ci_hdrc, gadget);
+	struct usb_ep *ep;
+
+	if (usb_endpoint_xfer_isoc(desc) && usb_endpoint_dir_in(desc)) {
+		list_for_each_entry_reverse(ep, &ci->gadget.ep_list, ep_list) {
+			if (ep->caps.dir_in && !ep->claimed)
+				return ep;
+		}
+	}
+
+	return NULL;
+}
+
 /**
  * Device operations part of the API to the USB controller hardware,
  * which don't involve endpoints (or i/o)
@@ -1627,6 +1646,7 @@ static const struct usb_gadget_ops usb_gadget_ops = {
 	.vbus_draw	= ci_udc_vbus_draw,
 	.udc_start	= ci_udc_start,
 	.udc_stop	= ci_udc_stop,
+	.match_ep 	= ci_udc_match_ep,
 };
 
 static int init_eps(struct ci_hdrc *ci)