On Wed, 11 Jan 2012, Sebastian Andrzej Siewior wrote: > The UAS driver requires SG support by the HCD operating the device. This > patch stops UAS from operating on a HCD without sg support and prints a > message to let him know. > > The spec says: > |For [USB2] backward compatibility, the device shall present [BOT] as > |alternate interface zero (primary) and [UAS] as alternate interface one > |(secondary). A device which does not need backward compatibility with > |[BOT] shall present [UAS] as alternate interface zero. In [USB2] > |systems, the [BOT] driver or an associated filter driver may need to > |issue a SET INTERFACE request for alternate interface one and then allow > |the [UAS] driver to load. > > If the user used usb_modeswitch to switch to UAS then he can go back to > BOT or use a different HCD. In case UAS is the only interface then there > is currently no way out. > In future usb_sg_wait() should be extended to provide a non-blocking > interface so it can work with the UAS driver. This approach looks okay to me. Hmmm, apparently nobody has yet modified usb-storage to skip devices with a UAS altsetting. When that gets added, we'll have to remember not to skip such devices if the HCD doesn't support SG (or if CONFIG_UAS isn't set, obviously). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
