[PATCH] USB: re-factor enumeration logic

This is an update to some patches from the December/January
timeframe, which will help sort out some of the mess for
drivers that need to use the reset logic.  It's one of the
last significant patches in my gadget-2.6 tree that haven't
yet been merged into the main kernel tree.


More refactoring of the enumeration code paths:

 * The first half of usb_new_device() becomes the second half of a new
   hub_port_init() routine (resets, sets address, gets descriptor)

 * The middle chunk of hub_port_connect_change() becomes the first half
   of that new hub_port_init() routine.

 * Khubd uses that new routine in hub_port_connect_change().

 * Now usb_new_device() cleans up better after faults, and has
   a more useful locking policy (caller owns dev->serialize).

 * Has related minor cleanups including commenting some of
   the curious request sequences coming from khubd.

Refactoring means a lot of the current usb_reset_device() logic won't
need to stay an imperfect clone of the enumeration code ... soon, it
can just call hub_port_init().

Even without touching usb_reset_device(), this eliminates a deadlock.
Previously, address0_sem was used both during probe and during reset,
so probe routines can't implement DFU firmware download (involves a
reset; DFU also uncovers other problems) or safely recover from probe
faults by resetting (usb-storage can try that).  Now that lock is no
longer held during probe(); so those deadlocks are gone.  (And some
drivers, like at76c503, can start to remove ugly workarounds.)

drivers/usb/core/hcd.c

@@ -779,10 +779,22 @@ int usb_register_root_hub (struct usb_device *usb_dev, struct device *parent_dev
 	set_bit (devnum, usb_dev->bus->devmap.devicemap);
 	usb_dev->state = USB_STATE_ADDRESS;
 
+	usb_dev->epmaxpacketin[0] = usb_dev->epmaxpacketout[0] = 64;
+	retval = usb_get_device_descriptor(usb_dev, USB_DT_DEVICE_SIZE);
+	if (retval != sizeof usb_dev->descriptor) {
+		dev_dbg (parent_dev, "can't read %s device descriptor %d\n",
+				usb_dev->dev.bus_id, retval);
+		return (retval < 0) ? retval : -EMSGSIZE;
+	}
+
+	(void) usb_get_dev (usb_dev);
+	down (&usb_dev->serialize);
 	retval = usb_new_device (usb_dev);
 	if (retval)
 		dev_err (parent_dev, "can't register root hub for %s, %d\n",
 				usb_dev->dev.bus_id, retval);
+	up (&usb_dev->serialize);
+	usb_put_dev (usb_dev);
 	return retval;
 }
 EXPORT_SYMBOL (usb_register_root_hub);

drivers/usb/core/hub.c

@@ -841,8 +841,11 @@ static int hub_port_status(struct usb_device *dev, int port,
 	return ret;
 }
 
-#define HUB_RESET_TRIES		5
-#define HUB_PROBE_TRIES		2
+#define PORT_RESET_TRIES	5
+#define SET_ADDRESS_TRIES	2
+#define GET_DESCRIPTOR_TRIES	2
+#define SET_CONFIG_TRIES	2
+
 #define HUB_ROOT_RESET_TIME	50	/* times are in msec */
 #define HUB_SHORT_RESET_TIME	10
 #define HUB_LONG_RESET_TIME	200
@@ -907,7 +910,7 @@ static int hub_port_reset(struct usb_device *hub, int port,
 	int i, status;
 
 	/* Reset the port */
-	for (i = 0; i < HUB_RESET_TRIES; i++) {
+	for (i = 0; i < PORT_RESET_TRIES; i++) {
 		set_port_feature(hub, port + 1, USB_PORT_FEAT_RESET);
 
 		/* return on disconnect or reset */
@@ -1003,40 +1006,20 @@ static int hub_port_debounce(struct usb_device *hub, int port)
 	return ((portstatus&USB_PORT_STAT_CONNECTION)) ? 0 : 1;
 }
 
-static void hub_port_connect_change(struct usb_hub *hubstate, int port,
-					u16 portstatus, u16 portchange)
+/* reset device, (re)assign address, get device descriptor.
+ * device connection is stable, no more debouncing needed.
+ * returns device in USB_STATE_ADDRESS, except on error.
+ * on error return, device is no longer usable (ref dropped).
+ *
+ * caller owns dev->serialize for the device, guarding against
+ * config changes and disconnect processing.
+ */
+static int
+hub_port_init (struct usb_device *hub, struct usb_device *dev, int port)
 {
-	struct usb_device *hub = interface_to_usbdev(hubstate->intf);
-	struct usb_device *dev;
-	unsigned int delay = HUB_SHORT_RESET_TIME;
-	int i;
-
-	dev_dbg (&hubstate->intf->dev,
-		"port %d, status %x, change %x, %s\n",
-		port + 1, portstatus, portchange, portspeed (portstatus));
-
-	/* Clear the connection change status */
-	clear_port_feature(hub, port + 1, USB_PORT_FEAT_C_CONNECTION);
-
-	/* Disconnect any existing devices under this port */
-	if (hub->children[port])
-		usb_disconnect(&hub->children[port]);
-
-	/* Return now if nothing is connected */
-	if (!(portstatus & USB_PORT_STAT_CONNECTION)) {
-		if (portstatus & USB_PORT_STAT_ENABLE)
-			hub_port_disable(hub, port);
-
-		return;
-	}
-
-	if (hub_port_debounce(hub, port)) {
-		dev_err (&hubstate->intf->dev,
-			"connect-debounce failed, port %d disabled\n",
-			port+1);
-		hub_port_disable(hub, port);
-		return;
-	}
+	int			i, j, retval = -ENODEV;
+	unsigned		delay = HUB_SHORT_RESET_TIME;
+	enum usb_device_speed	oldspeed = dev->speed;
 
 	/* root hub ports have a slightly longer reset period
 	 * (from USB 2.0 spec, section 7.1.7.5)
@@ -1046,31 +1029,53 @@ static void hub_port_connect_change(struct usb_hub *hubstate, int port,
 
 	/* Some low speed devices have problems with the quick delay, so */
 	/*  be a bit pessimistic with those devices. RHbug #23670 */
-	if (portstatus & USB_PORT_STAT_LOW_SPEED)
+	if (oldspeed == USB_SPEED_LOW)
 		delay = HUB_LONG_RESET_TIME;
 
 	down(&usb_address0_sem);
 
-	for (i = 0; i < HUB_PROBE_TRIES; i++) {
-
-		/* Allocate a new device struct */
-		dev = usb_alloc_dev(hub, hub->bus, port);
-		if (!dev) {
-			dev_err (&hubstate->intf->dev,
-				"couldn't allocate usb_device\n");
+	/* Reset the device; full speed may morph to high speed */
+	switch (hub_port_reset(hub, port, dev, delay)) {
+	case 0:			/* success, speed is known */
 		break;
+	case 1:			/* disconnect, give to companion */
+		retval = -EBUSY;
+		/* FALL THROUGH */
+	default:		/* error */
+		goto fail;
+	}
+	if (oldspeed != USB_SPEED_UNKNOWN && oldspeed != dev->speed) {
+		dev_dbg(&dev->dev, "device reset changed speed!\n");
+		goto fail;
 	}
   
-		dev->state = USB_STATE_POWERED;
-
-		/* Reset the device, and detect its speed */
-		if (hub_port_reset(hub, port, dev, delay)) {
-			usb_put_dev(dev);
+	/* USB 2.0 section 5.5.3 talks about ep0 maxpacket ...
+	 * it's fixed size except for full speed devices.
+	 */
+	switch (dev->speed) {
+	case USB_SPEED_HIGH:		/* fixed at 64 */
+		i = 64;
+		break;
+	case USB_SPEED_FULL:		/* 8, 16, 32, or 64 */
+		/* to determine the ep0 maxpacket size, read the first 8
+		 * bytes from the device descriptor to get bMaxPacketSize0;
+		 * then correct our initial (small) guess.
+		 */
+		// FALLTHROUGH
+	case USB_SPEED_LOW:		/* fixed at 8 */
+		i = 8;
 		break;
+	default:
+		goto fail;
 	}
+	dev->epmaxpacketin [0] = i;
+	dev->epmaxpacketout[0] = i;
  
-		/* Find a new address for it */
+	/* set the address */
+	if (dev->devnum <= 0) {
 		usb_choose_address(dev);
+		if (dev->devnum <= 0)
+			goto fail;
 
 		/* Set up TT records, if needed  */
 		if (hub->tt) {
@@ -1078,12 +1083,21 @@ static void hub_port_connect_change(struct usb_hub *hubstate, int port,
 			dev->ttport = hub->ttport;
 		} else if (dev->speed != USB_SPEED_HIGH
 				&& hub->speed == USB_SPEED_HIGH) {
+			struct usb_hub	*hubstate;
+ 
+			hubstate = usb_get_intfdata (hub->actconfig
+							->interface[0]);
 			dev->tt = &hubstate->tt;
 			dev->ttport = port + 1;
 		}
 
+		/* force the right log message (below) at low speed */
+		oldspeed = USB_SPEED_UNKNOWN;
+	}
+ 
 	dev_info (&dev->dev,
-			"new %s speed USB device using address %d\n",
+			"%s %s speed USB device using address %d\n",
+			(oldspeed == USB_SPEED_UNKNOWN) ? "new" : "reset",
 			({ char *speed; switch (dev->speed) {
 			case USB_SPEED_LOW:	speed = "low";	break;
 			case USB_SPEED_FULL:	speed = "full";	break;
@@ -1092,22 +1106,154 @@ static void hub_port_connect_change(struct usb_hub *hubstate, int port,
 			}; speed;}),
 			dev->devnum);
  
-		/* Run it through the hoops (find a driver, etc) */
-		if (usb_new_device(dev) == 0) {
+	/* Why interleave GET_DESCRIPTOR and SET_ADDRESS this way?
+	 * Because device hardware and firmware is sometimes buggy in
+	 * this area, and this is how Linux has done it for ages.
+	 * Change it cautiously.
+	 *
+	 * NOTE:  Windows gets the descriptor first, seemingly to help
+	 * work around device bugs like "can't use addresses with bit 3
+	 * set in certain configurations".  Yes, really.
+	 */
+	for (i = 0; i < GET_DESCRIPTOR_TRIES; ++i) {
+		for (j = 0; j < SET_ADDRESS_TRIES; ++j) {
+			retval = usb_set_address(dev);
+			if (retval >= 0)
+				break;
+			wait_ms(200);
+		}
+		if (retval < 0) {
+			dev_err(&dev->dev,
+				"device not accepting address %d, error %d\n",
+				dev->devnum, retval);
+ fail:
+			hub_port_disable(hub, port);
+			clear_bit(dev->devnum, dev->bus->devmap.devicemap);
+			dev->devnum = -1;
+			usb_put_dev(dev);
+			up(&usb_address0_sem);
+			return retval;
+		}
+ 
+		/* cope with hardware quirkiness:
+		 *  - let SET_ADDRESS settle, some device hardware wants it
+		 *  - read ep0 maxpacket even for high and low speed,
+  		 */
+		wait_ms(10);
+		retval = usb_get_device_descriptor(dev, 8);
+		if (retval >= 8)
+			break;
+		wait_ms(100);
+	}
+	if (retval != 8) {
+		dev_err(&dev->dev, "device descriptor read/%s, error %d\n",
+				"8", retval);
+		if (retval >= 0)
+			retval = -EMSGSIZE;
+		goto fail;
+	}
+	if (dev->speed == USB_SPEED_FULL
+			&& (dev->epmaxpacketin [0]
+				!= dev->descriptor.bMaxPacketSize0)) {
+		usb_disable_endpoint(dev, 0);
+		usb_endpoint_running(dev, 0, 1);
+		usb_endpoint_running(dev, 0, 0);
+		dev->epmaxpacketin [0] = dev->descriptor.bMaxPacketSize0;
+		dev->epmaxpacketout[0] = dev->descriptor.bMaxPacketSize0;
+	}
+  
+	retval = usb_get_device_descriptor(dev, USB_DT_DEVICE_SIZE);
+	if (retval < (signed)sizeof(dev->descriptor)) {
+		dev_err(&dev->dev, "device descriptor read/%s, error %d\n",
+			"all", retval);
+		if (retval >= 0)
+			retval = -ENOMSG;
+		goto fail;
+	}
+
+	/* now dev is visible to other tasks */
 	hub->children[port] = dev;
+
+	up(&usb_address0_sem);
+	return 0;
+}
+
+static void hub_port_connect_change(struct usb_hub *hubstate, int port,
+					u16 portstatus, u16 portchange)
+{
+	struct usb_device *hub = interface_to_usbdev(hubstate->intf);
+	int status, i;
+ 
+	dev_dbg (&hubstate->intf->dev,
+		"port %d, status %04x, change %04x, %s\n",
+		port + 1, portstatus, portchange, portspeed (portstatus));
+ 
+	/* Clear the connection change status */
+	clear_port_feature(hub, port + 1, USB_PORT_FEAT_C_CONNECTION);
+
+	if (hubstate->has_indicators) {
+		set_port_led(hub, hubstate, port + 1, HUB_LED_AUTO);
+		hubstate->indicator[port] = INDICATOR_AUTO;
+	}
+ 
+	/* Disconnect any existing devices under this port */
+	if (hub->children[port])
+		usb_disconnect(&hub->children[port]);
+ 
+	/* Return now if nothing is connected */
+	if (!(portstatus & USB_PORT_STAT_CONNECTION)) {
+		if (portstatus & USB_PORT_STAT_ENABLE)
   			goto done;
+		return;
 	}
   
-		/* Free the configuration if there was an error */
-		usb_put_dev(dev);
+	if (hub_port_debounce(hub, port)) {
+		dev_err (&hubstate->intf->dev,
+			"connect-debounce failed, port %d disabled\n",
+			port+1);
+		goto done;
+	}
 
-		/* Switch to a long reset time */
-		delay = HUB_LONG_RESET_TIME;
+	for (i = 0; i < SET_CONFIG_TRIES; i++) {
+		struct usb_device *dev;
+
+		/* reallocate for each attempt, since references
+		 * to the previous one can escape in various ways
+		 */
+		dev = usb_alloc_dev(hub, hub->bus, port);
+		if (!dev) {
+			dev_err (&hubstate->intf->dev,
+				"couldn't allocate port %d usb_device\n", port+1);
+			goto done;
 		}
+		dev->state = USB_STATE_POWERED;
 	  
-	hub_port_disable(hub, port);
+		/* hub can tell if it's lowspeed already:  D- pullup (not D+) */
+		if (portstatus & USB_PORT_STAT_LOW_SPEED)
+			dev->speed = USB_SPEED_LOW;
+		else
+			dev->speed = USB_SPEED_UNKNOWN;
+
+		/* reset, set address, get descriptor, add to hub's children */
+		down (&dev->serialize);
+		status = hub_port_init(hub, dev, port);
+		if (status == -EBUSY)
+			break;
+		if (status < 0)
+			continue;
+ 
+		/* Run it through the hoops (find a driver, etc) */
+		status = usb_new_device(dev);
+		if (status != 0) {
+			hub->children[port] = NULL;
+			continue;
+		}
+
+		up (&dev->serialize);
+		return;
+	}
 done:
-	up(&usb_address0_sem);
+	hub_port_disable(hub, port);
 }
 
 static void hub_events(void)
@@ -1285,9 +1431,6 @@ static struct usb_driver hub_driver = {
 	.id_table =	hub_id_table,
 };
 
-/*
- * This should be a separate module.
- */
 int usb_hub_init(void)
 {
 	pid_t pid;

drivers/usb/core/usb.c

@@ -1064,92 +1064,29 @@ static inline void usb_show_string(struct usb_device *dev, char *id, int index)
 }
 
 /*
- * By the time we get here, we chose a new device address
- * and is in the default state. We need to identify the thing and
- * get the ball rolling..
+ * usb_new_device - perform initial device setup (usbcore-internal)
+ * @dev: newly addressed device (in ADDRESS state)
  *
- * Returns 0 for success, != 0 for error.
+ * This is called with devices which have been enumerated, but not yet
+ * configured.  The device descriptor is available, but not descriptors
+ * for any device configuration.  The caller owns dev->serialize, and
+ * the device is not visible through sysfs or other filesystem code.
+ *
+ * Returns 0 for success (device is configured and listed, with its
+ * interfaces, in sysfs); else a negative errno value.  On error, one
+ * reference count to the device has been dropped.
  *
  * This call is synchronous, and may not be used in an interrupt context.
  *
  * Only the hub driver should ever call this; root hub registration
  * uses it only indirectly.
  */
-#define NEW_DEVICE_RETRYS	2
-#define SET_ADDRESS_RETRYS	2
 int usb_new_device(struct usb_device *dev)
 {
-	int err = -EINVAL;
+	int err;
 	int i;
-	int j;
 	int config;
 
-	/* USB 2.0 section 5.5.3 talks about ep0 maxpacket ...
-	 * it's fixed size except for full speed devices.
-	 */
-	switch (dev->speed) {
-	case USB_SPEED_HIGH:		/* fixed at 64 */
-		i = 64;
-		break;
-	case USB_SPEED_FULL:		/* 8, 16, 32, or 64 */
-		/* to determine the ep0 maxpacket size, read the first 8
-		 * bytes from the device descriptor to get bMaxPacketSize0;
-		 * then correct our initial (small) guess.
-		 */
-		// FALLTHROUGH
-	case USB_SPEED_LOW:		/* fixed at 8 */
-		i = 8;
-		break;
-	default:
-		goto fail;
-	}
-	dev->epmaxpacketin [0] = i;
-	dev->epmaxpacketout[0] = i;
-
-	for (i = 0; i < NEW_DEVICE_RETRYS; ++i) {
-
-		for (j = 0; j < SET_ADDRESS_RETRYS; ++j) {
-			err = usb_set_address(dev);
-			if (err >= 0)
-				break;
-			wait_ms(200);
-		}
-		if (err < 0) {
-			dev_err(&dev->dev,
-				"device not accepting address %d, error %d\n",
-				dev->devnum, err);
-			goto fail;
-		}
-
-		wait_ms(10);	/* Let the SET_ADDRESS settle */
-
-		/* high and low speed devices don't need this... */
-		err = usb_get_device_descriptor(dev, 8);
-		if (err >= 8)
-			break;
-		wait_ms(100);
-	}
-
-	if (err < 8) {
-		dev_err(&dev->dev, "device descriptor read/8, error %d\n", err);
-		goto fail;
-	}
-	if (dev->speed == USB_SPEED_FULL) {
-		usb_disable_endpoint(dev, 0);
-		usb_endpoint_running(dev, 0, 1);
-		usb_endpoint_running(dev, 0, 0);
-		dev->epmaxpacketin [0] = dev->descriptor.bMaxPacketSize0;
-		dev->epmaxpacketout[0] = dev->descriptor.bMaxPacketSize0;
-	}
-
-	/* USB device state == addressed ... still not usable */
-
-	err = usb_get_device_descriptor(dev, sizeof(dev->descriptor));
-	if (err != (signed)sizeof(dev->descriptor)) {
-		dev_err(&dev->dev, "device descriptor read/all, error %d\n", err);
-		goto fail;
-	}
-
 	err = usb_get_configuration(dev);
 	if (err < 0) {
 		dev_err(&dev->dev, "can't read configurations, error %d\n",
@@ -1170,13 +1107,10 @@ int usb_new_device(struct usb_device *dev)
 		usb_show_string(dev, "SerialNumber", dev->descriptor.iSerialNumber);
 #endif
 
-	down(&dev->serialize);
-
 	/* put device-specific files into sysfs */
 	err = device_add (&dev->dev);
 	if (err) {
 		dev_err(&dev->dev, "can't device_add, error %d\n", err);
-		up(&dev->serialize);
 		goto fail;
 	}
 	usb_create_driverfs_dev_files (dev);
@@ -1211,7 +1145,6 @@ int usb_new_device(struct usb_device *dev)
 			dev->descriptor.bNumConfigurations);
 	}
 	err = usb_set_configuration(dev, config);
-	up(&dev->serialize);
 	if (err) {
 		dev_err(&dev->dev, "can't set config #%d, error %d\n",
 			config, err);
@@ -1226,9 +1159,10 @@ int usb_new_device(struct usb_device *dev)
 
 	return 0;
 fail:
-	dev->state = USB_STATE_DEFAULT;
+	dev->state = USB_STATE_NOTATTACHED;
 	clear_bit(dev->devnum, dev->bus->devmap.devicemap);
 	dev->devnum = -1;
+	usb_put_dev(dev);
 	return err;
 }