USB: Support for bandwidth allocation.

Originally, the USB core had no support for allocating bandwidth when a
particular configuration or alternate setting for an interface was
selected.  Instead, the device driver's URB submission would fail if
there was not enough bandwidth for a periodic endpoint.  Drivers could
work around this, by using the scatter-gather list API to guarantee
bandwidth.

This patch adds host controller API to allow the USB core to allocate or
deallocate bandwidth for an endpoint.  Endpoints are added to or dropped
from a copy of the current schedule by calling add_endpoint() or
drop_endpoint(), and then the schedule is atomically evaluated with a
call to check_bandwidth().  This allows all the endpoints for a new
configuration or alternate setting to be added at the same time that the
endpoints from the old configuration or alt setting are dropped.

Endpoints must be added to the schedule before any URBs are submitted to
them.  The HCD must be allowed to reject a new configuration or alt
setting before the control transfer is sent to the device requesting the
change.  It may reject the change because there is not enough bandwidth,
not enough internal resources (such as memory on an embedded host
controller), or perhaps even for security reasons in a virtualized
environment.

If the call to check_bandwidth() fails, the USB core must call
reset_bandwidth().  This causes the schedule to be reverted back to the
state it was in just after the last successful check_bandwidth() call.

If the call succeeds, the host controller driver (and hardware) will have
changed its internal state to match the new configuration or alternate
setting.  The USB core can then issue a control transfer to the device to
change the configuration or alt setting.  This allows the core to test new
configurations or alternate settings before unbinding drivers bound to
interfaces in the old configuration.

WIP:

The USB core must add endpoints from all interfaces in a configuration
to the schedule, because a driver may claim that interface at any time.
A slight optimization might be to add the endpoints to the schedule once
a driver claims that interface.  FIXME

This patch does not cover changing alternate settings, but it does
handle a configuration change or de-configuration.  FIXME

The code for managing the schedule is currently HCD specific.  A generic
scheduling algorithm could be added for host controllers without
built-in scheduling support.  For now, if a host controller does not
define the check_bandwidth() function, the call to
usb_hcd_check_bandwidth() will always succeed.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 32 insertions, 0 deletions

diff --git a/drivers/usb/core/hcd.h b/drivers/usb/core/hcd.h
index ae6d9db41ca9..d397ecfd5b17 100644
--- a/drivers/usb/core/hcd.h
+++ b/drivers/usb/core/hcd.h
@@ -232,6 +232,35 @@ struct hc_driver {
 	int	(*alloc_dev)(struct usb_hcd *, struct usb_device *);
 		/* Called by usb_release_dev to free HC device structures */
 	void	(*free_dev)(struct usb_hcd *, struct usb_device *);
+
+	/* Bandwidth computation functions */
+	/* Note that add_endpoint() can only be called once per endpoint before
+	 * check_bandwidth() or reset_bandwidth() must be called.
+	 * drop_endpoint() can only be called once per endpoint also.
+	 * A call to xhci_drop_endpoint() followed by a call to xhci_add_endpoint() will
+	 * add the endpoint to the schedule with possibly new parameters denoted by a
+	 * different endpoint descriptor in usb_host_endpoint.
+	 * A call to xhci_add_endpoint() followed by a call to xhci_drop_endpoint() is
+	 * not allowed.
+	 */
+		/* Allocate endpoint resources and add them to a new schedule */
+	int 	(*add_endpoint)(struct usb_hcd *, struct usb_device *, struct usb_host_endpoint *);
+		/* Drop an endpoint from a new schedule */
+	int 	(*drop_endpoint)(struct usb_hcd *, struct usb_device *, struct usb_host_endpoint *);
+		/* Check that a new hardware configuration, set using
+		 * endpoint_enable and endpoint_disable, does not exceed bus
+		 * bandwidth.  This must be called before any set configuration
+		 * or set interface requests are sent to the device.
+		 */
+	int	(*check_bandwidth)(struct usb_hcd *, struct usb_device *);
+		/* Reset the device schedule to the last known good schedule,
+		 * which was set from a previous successful call to
+		 * check_bandwidth().  This reverts any add_endpoint() and
+		 * drop_endpoint() calls since that last successful call.
+		 * Used for when a check_bandwidth() call fails due to resource
+		 * or bandwidth constraints.
+		 */
+	void	(*reset_bandwidth)(struct usb_hcd *, struct usb_device *);
 		/* Returns the hardware-chosen device address */
 	int	(*address_device)(struct usb_hcd *, struct usb_device *udev);
 };
@@ -252,6 +281,9 @@ extern void usb_hcd_disable_endpoint(struct usb_device *udev,
 extern void usb_hcd_reset_endpoint(struct usb_device *udev,
 		struct usb_host_endpoint *ep);
 extern void usb_hcd_synchronize_unlinks(struct usb_device *udev);
+extern int usb_hcd_check_bandwidth(struct usb_device *udev,
+		struct usb_host_config *new_config,
+		struct usb_interface *new_intf);
 extern int usb_hcd_get_frame_number(struct usb_device *udev);
 
 extern struct usb_hcd *usb_create_hcd(const struct hc_driver *driver,