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79abb1ab13
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> |
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