Multiple-Configuration Devices

USB devices make only a single configuration available to the host at any particular time. Most devices support only a single configuration. However, a few USB devices support multiple configurations.

Any device that has multiple configurations is placed into the first configuration for which a driver is available. When seeking a match, device configurations are considered in numeric order. If no matching driver is found, the device is set to the first configuration. In this case, the usb_mid driver takes over the device and splits the device into interface nodes. Use the usb_get_cfg(9F) function to return the current configuration of a device.

You can use either of the following two methods to request a different configuration. Using either of these two methods to modify the device configuration ensures that the USBA module remains in sync with the device.

• Use the cfgadm_usb(1M) command.

• Call the usb_set_cfg(9F) function from the driver.

  Because changing device configuration affects an entire device, the client driver must meet all of the following criteria to call the usb_set_cfg(9F) function successfully:

  • The client driver must own the entire device.

  • The device must have no child nodes, because other drivers could drive the device through them.

  • All pipes except the default pipe must be closed.

  • The device must have multiple configurations.

Do not change the device configuration by doing a SET_CONFIGURATION USB request manually. Using a SET_CONFIGURATION request to change the configuration is not supported.