[PATCH] USB: Consider power budget when choosing configuration

This patch (as609) changes the way we keep track of power budgeting for
USB hubs and devices, and it updates the choose_configuration routine to
take this information into account.  (This is something we should have
been doing all along.)  A new field in struct usb_device holds the amount
of bus current available from the upstream port, and the usb_hub structure
keeps track of the current available for each downstream port.

Two new rules for configuration selection are added:

	Don't select a self-powered configuration when only bus power
	is available.

	Don't select a configuration requiring more bus power than is
	available.

However the first rule is #if-ed out, because I found that the internal
hub in my HP USB keyboard claims that its only configuration is
self-powered.  The rule would prevent the configuration from being chosen,
leaving the hub & keyboard unconfigured.  Since similar descriptor errors
may turn out to be fairly common, it seemed wise not to include a rule
that would break automatic configuration unnecessarily for such devices.

The second rule may also trigger unnecessarily, although this should be
less common.  More likely it will annoy people by sometimes failing to
accept configurations that should never have been chosen in the first
place.

The patch also changes usbcore's reaction when no configuration is
suitable.  Instead of raising an error and rejecting the device, now
the core will simply leave the device unconfigured.  People can always
work around such problems by installing configurations manually through
sysfs.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/hcd.c

@@ -1825,8 +1825,6 @@ int usb_add_hcd(struct usb_hcd *hcd,
 		retval = -ENOMEM;
 		goto err_allocate_root_hub;
 	}
-	rhdev->speed = (hcd->driver->flags & HCD_USB2) ? USB_SPEED_HIGH :
-			USB_SPEED_FULL;
 
 	/* Although in principle hcd->driver->start() might need to use rhdev,
 	 * none of the current drivers do.
@@ -1844,6 +1842,9 @@ int usb_add_hcd(struct usb_hcd *hcd,
 		dev_dbg(hcd->self.controller, "supports USB remote wakeup\n");
 	hcd->remote_wakeup = hcd->can_wakeup;
 
+	rhdev->speed = (hcd->driver->flags & HCD_USB2) ? USB_SPEED_HIGH :
+			USB_SPEED_FULL;
+	rhdev->bus_mA = min(500u, hcd->power_budget);
 	if ((retval = register_root_hub(rhdev, hcd)) != 0)
 		goto err_register_root_hub;
 

drivers/usb/core/hub.c

@@ -702,26 +702,40 @@ static int hub_configure(struct usb_hub *hub,
 	 * and battery-powered root hubs (may provide just 8 mA).
 	 */
 	ret = usb_get_status(hdev, USB_RECIP_DEVICE, 0, &hubstatus);
-	if (ret < 0) {
+	if (ret < 2) {
 		message = "can't get hub status";
 		goto fail;
 	}
 	le16_to_cpus(&hubstatus);
 	if (hdev == hdev->bus->root_hub) {
-		struct usb_hcd *hcd =
-				container_of(hdev->bus, struct usb_hcd, self);
-
-		hub->power_budget = min(500u, hcd->power_budget) / 2;
+		if (hdev->bus_mA == 0 || hdev->bus_mA >= 500)
+			hub->mA_per_port = 500;
+		else {
+			hub->mA_per_port = hdev->bus_mA;
+			hub->limited_power = 1;
+		}
 	} else if ((hubstatus & (1 << USB_DEVICE_SELF_POWERED)) == 0) {
 		dev_dbg(hub_dev, "hub controller current requirement: %dmA\n",
 			hub->descriptor->bHubContrCurrent);
-		hub->power_budget = (501 - hub->descriptor->bHubContrCurrent)
-					/ 2;
+		hub->limited_power = 1;
+		if (hdev->maxchild > 0) {
+			int remaining = hdev->bus_mA -
+					hub->descriptor->bHubContrCurrent;
+
+			if (remaining < hdev->maxchild * 100)
+				dev_warn(hub_dev,
+					"insufficient power available "
+					"to use all downstream ports\n");
+			hub->mA_per_port = 100;		/* 7.2.1.1 */
+		}
+	} else {	/* Self-powered external hub */
+		/* FIXME: What about battery-powered external hubs that
+		 * provide less current per port? */
+		hub->mA_per_port = 500;
 	}
-	if (hub->power_budget)
-		dev_dbg(hub_dev, "%dmA bus power budget for children\n",
-			hub->power_budget * 2);
-
+	if (hub->mA_per_port < 500)
+		dev_dbg(hub_dev, "%umA bus power budget for each child\n",
+				hub->mA_per_port);
 
 	ret = hub_hub_status(hub, &hubstatus, &hubchange);
 	if (ret < 0) {
@@ -1136,45 +1150,107 @@ void usb_disconnect(struct usb_device **pdev)
 	device_unregister(&udev->dev);
 }
 
+static inline const char *plural(int n)
+{
+	return (n == 1 ? "" : "s");
+}
+
 static int choose_configuration(struct usb_device *udev)
 {
-	int c, i;
+	int i;
+	u16 devstatus;
+	int bus_powered;
+	int num_configs;
+	struct usb_host_config *c, *best;
+
+	/* If this fails, assume the device is bus-powered */
+	devstatus = 0;
+	usb_get_status(udev, USB_RECIP_DEVICE, 0, &devstatus);
+	le16_to_cpus(&devstatus);
+	bus_powered = ((devstatus & (1 << USB_DEVICE_SELF_POWERED)) == 0);
+	dev_dbg(&udev->dev, "device is %s-powered\n",
+			bus_powered ? "bus" : "self");
+
+	best = NULL;
+	c = udev->config;
+	num_configs = udev->descriptor.bNumConfigurations;
+	for (i = 0; i < num_configs; (i++, c++)) {
+		struct usb_interface_descriptor	*desc =
+				&c->intf_cache[0]->altsetting->desc;
+
+		/*
+		 * HP's USB bus-powered keyboard has only one configuration
+		 * and it claims to be self-powered; other devices may have
+		 * similar errors in their descriptors.  If the next test
+		 * were allowed to execute, such configurations would always
+		 * be rejected and the devices would not work as expected.
+		 */
+#if 0
+		/* Rule out self-powered configs for a bus-powered device */
+		if (bus_powered && (c->desc.bmAttributes &
+					USB_CONFIG_ATT_SELFPOWER))
+			continue;
+#endif
 
-	/* NOTE: this should interact with hub power budgeting */
+		/*
+		 * The next test may not be as effective as it should be.
+		 * Some hubs have errors in their descriptor, claiming
+		 * to be self-powered when they are really bus-powered.
+		 * We will overestimate the amount of current such hubs
+		 * make available for each port.
+		 *
+		 * This is a fairly benign sort of failure.  It won't
+		 * cause us to reject configurations that we should have
+		 * accepted.
+		 */
 
-	c = udev->config[0].desc.bConfigurationValue;
-	if (udev->descriptor.bNumConfigurations != 1) {
-		for (i = 0; i < udev->descriptor.bNumConfigurations; i++) {
-			struct usb_interface_descriptor	*desc;
+		/* Rule out configs that draw too much bus current */
+		if (c->desc.bMaxPower * 2 > udev->bus_mA)
+			continue;
 
-			/* heuristic:  Linux is more likely to have class
-			 * drivers, so avoid vendor-specific interfaces.
-			 */
-			desc = &udev->config[i].intf_cache[0]
-					->altsetting->desc;
-			if (desc->bInterfaceClass == USB_CLASS_VENDOR_SPEC)
-				continue;
-			/* COMM/2/all is CDC ACM, except 0xff is MSFT RNDIS.
-			 * MSFT needs this to be the first config; never use
-			 * it as the default unless Linux has host-side RNDIS.
-			 * A second config would ideally be CDC-Ethernet, but
-			 * may instead be the "vendor specific" CDC subset
-			 * long used by ARM Linux for sa1100 or pxa255.
-			 */
-			if (desc->bInterfaceClass == USB_CLASS_COMM
-					&& desc->bInterfaceSubClass == 2
-					&& desc->bInterfaceProtocol == 0xff) {
-				c = udev->config[1].desc.bConfigurationValue;
-				continue;
-			}
-			c = udev->config[i].desc.bConfigurationValue;
+		/* If the first config's first interface is COMM/2/0xff
+		 * (MSFT RNDIS), rule it out unless Linux has host-side
+		 * RNDIS support. */
+		if (i == 0 && desc->bInterfaceClass == USB_CLASS_COMM
+				&& desc->bInterfaceSubClass == 2
+				&& desc->bInterfaceProtocol == 0xff) {
+#ifndef CONFIG_USB_NET_RNDIS
+			continue;
+#else
+			best = c;
+#endif
+		}
+
+		/* From the remaining configs, choose the first one whose
+		 * first interface is for a non-vendor-specific class.
+		 * Reason: Linux is more likely to have a class driver
+		 * than a vendor-specific driver. */
+		else if (udev->descriptor.bDeviceClass !=
+						USB_CLASS_VENDOR_SPEC &&
+				desc->bInterfaceClass !=
+						USB_CLASS_VENDOR_SPEC) {
+			best = c;
 			break;
 		}
+
+		/* If all the remaining configs are vendor-specific,
+		 * choose the first one. */
+		else if (!best)
+			best = c;
+	}
+
+	if (best) {
+		i = best->desc.bConfigurationValue;
 		dev_info(&udev->dev,
-			"configuration #%d chosen from %d choices\n",
-			c, udev->descriptor.bNumConfigurations);
+			"configuration #%d chosen from %d choice%s\n",
+			i, num_configs, plural(num_configs));
+	} else {
+		i = -1;
+		dev_warn(&udev->dev,
+			"no configuration chosen from %d choice%s\n",
+			num_configs, plural(num_configs));
 	}
-	return c;
+	return i;
 }
 
 #ifdef DEBUG
@@ -1327,17 +1403,13 @@ int usb_new_device(struct usb_device *udev)
 	 * with the driver core, and lets usb device drivers bind to them.
 	 */
 	c = choose_configuration(udev);
-	if (c < 0)
-		dev_warn(&udev->dev,
-				"can't choose an initial configuration\n");
-	else {
+	if (c >= 0) {
 		err = usb_set_configuration(udev, c);
 		if (err) {
 			dev_err(&udev->dev, "can't set config #%d, error %d\n",
 					c, err);
-			usb_remove_sysfs_dev_files(udev);
-			device_del(&udev->dev);
-			goto fail;
+			/* This need not be fatal.  The user can try to
+			 * set other configurations. */
 		}
 	}
 
@@ -1702,7 +1774,7 @@ static int finish_device_resume(struct usb_device *udev)
 	 * and device drivers will know about any resume quirks.
 	 */
 	status = usb_get_status(udev, USB_RECIP_DEVICE, 0, &devstatus);
-	if (status < 0)
+	if (status < 2)
 		dev_dbg(&udev->dev,
 			"gone after usb resume? status %d\n",
 			status);
@@ -1711,7 +1783,7 @@ static int finish_device_resume(struct usb_device *udev)
 		int		(*resume)(struct device *);
 
 		le16_to_cpus(&devstatus);
-		if (devstatus & (1 << USB_DEVICE_REMOTE_WAKEUP)
+		if ((devstatus & (1 << USB_DEVICE_REMOTE_WAKEUP))
 				&& udev->parent) {
 			status = usb_control_msg(udev,
 					usb_sndctrlpipe(udev, 0),
@@ -2374,39 +2446,36 @@ hub_power_remaining (struct usb_hub *hub)
 {
 	struct usb_device *hdev = hub->hdev;
 	int remaining;
-	unsigned i;
+	int port1;
 
-	remaining = hub->power_budget;
-	if (!remaining)		/* self-powered */
+	if (!hub->limited_power)
 		return 0;
 
-	for (i = 0; i < hdev->maxchild; i++) {
-		struct usb_device	*udev = hdev->children[i];
-		int			delta, ceiling;
+	remaining = hdev->bus_mA - hub->descriptor->bHubContrCurrent;
+	for (port1 = 1; port1 <= hdev->maxchild; ++port1) {
+		struct usb_device	*udev = hdev->children[port1 - 1];
+		int			delta;
 
 		if (!udev)
 			continue;
 
-		/* 100mA per-port ceiling, or 8mA for OTG ports */
-		if (i != (udev->bus->otg_port - 1) || hdev->parent)
-			ceiling = 50;
-		else
-			ceiling = 4;
-
+		/* Unconfigured devices may not use more than 100mA,
+		 * or 8mA for OTG ports */
 		if (udev->actconfig)
-			delta = udev->actconfig->desc.bMaxPower;
+			delta = udev->actconfig->desc.bMaxPower * 2;
+		else if (port1 != udev->bus->otg_port || hdev->parent)
+			delta = 100;
 		else
-			delta = ceiling;
-		// dev_dbg(&udev->dev, "budgeted %dmA\n", 2 * delta);
-		if (delta > ceiling)
-			dev_warn(&udev->dev, "%dmA over %dmA budget!\n",
-				2 * (delta - ceiling), 2 * ceiling);
+			delta = 8;
+		if (delta > hub->mA_per_port)
+			dev_warn(&udev->dev, "%dmA is over %umA budget "
+					"for port %d!\n",
+					delta, hub->mA_per_port, port1);
 		remaining -= delta;
 	}
 	if (remaining < 0) {
-		dev_warn(hub->intfdev,
-			"%dmA over power budget!\n",
-			-2 * remaining);
+		dev_warn(hub->intfdev, "%dmA over power budget!\n",
+			- remaining);
 		remaining = 0;
 	}
 	return remaining;
@@ -2501,7 +2570,8 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
 
 		usb_set_device_state(udev, USB_STATE_POWERED);
 		udev->speed = USB_SPEED_UNKNOWN;
-
+ 		udev->bus_mA = hub->mA_per_port;
+
 		/* set the address */
 		choose_address(udev);
 		if (udev->devnum <= 0) {
@@ -2521,16 +2591,16 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
 		 * on the parent.
 		 */
 		if (udev->descriptor.bDeviceClass == USB_CLASS_HUB
-				&& hub->power_budget) {
+				&& udev->bus_mA <= 100) {
 			u16	devstat;
 
 			status = usb_get_status(udev, USB_RECIP_DEVICE, 0,
 					&devstat);
-			if (status < 0) {
+			if (status < 2) {
 				dev_dbg(&udev->dev, "get status %d ?\n", status);
 				goto loop_disable;
 			}
-			cpu_to_le16s(&devstat);
+			le16_to_cpus(&devstat);
 			if ((devstat & (1 << USB_DEVICE_SELF_POWERED)) == 0) {
 				dev_err(&udev->dev,
 					"can't connect bus-powered hub "
@@ -2583,9 +2653,7 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
 
 		status = hub_power_remaining(hub);
 		if (status)
-			dev_dbg(hub_dev,
-				"%dmA power budget left\n",
-				2 * status);
+			dev_dbg(hub_dev, "%dmA power budget left\n", status);
 
 		return;
 
@@ -2797,6 +2865,11 @@ static void hub_events(void)
 			if (hubchange & HUB_CHANGE_LOCAL_POWER) {
 				dev_dbg (hub_dev, "power change\n");
 				clear_hub_feature(hdev, C_HUB_LOCAL_POWER);
+				if (hubstatus & HUB_STATUS_LOCAL_POWER)
+					/* FIXME: Is this always true? */
+					hub->limited_power = 0;
+				else
+					hub->limited_power = 1;
 			}
 			if (hubchange & HUB_CHANGE_OVERCURRENT) {
 				dev_dbg (hub_dev, "overcurrent change\n");

drivers/usb/core/hub.h

@@ -220,8 +220,9 @@ struct usb_hub {
 	struct usb_hub_descriptor *descriptor;	/* class descriptor */
 	struct usb_tt		tt;		/* Transaction Translator */
 
-	u8			power_budget;	/* in 2mA units; or zero */
+	unsigned		mA_per_port;	/* current for each child */
 
+	unsigned		limited_power:1;
 	unsigned		quiescing:1;
 	unsigned		activating:1;
 	unsigned		resume_root_hub:1;

drivers/usb/core/message.c

@@ -1387,6 +1387,12 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
 	if (dev->state != USB_STATE_ADDRESS)
 		usb_disable_device (dev, 1);	// Skip ep0
 
+	n = dev->bus_mA - cp->desc.bMaxPower * 2;
+	if (n < 0)
+		dev_warn(&dev->dev, "new config #%d exceeds power "
+				"limit by %dmA\n",
+				configuration, -n);
+
 	if ((ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
 			USB_REQ_SET_CONFIGURATION, 0, configuration, 0,
 			NULL, 0, USB_CTRL_SET_TIMEOUT)) < 0)

include/linux/usb.h

@@ -347,6 +347,8 @@ struct usb_device {
 
 	char **rawdescriptors;		/* Raw descriptors for each config */
 
+	unsigned short bus_mA;		/* Current available from the bus */
+
 	int have_langid;		/* whether string_langid is valid */
 	int string_langid;		/* language ID for strings */