On Sun, 24 Aug 2014, vichy wrote: > hi all: > below patch introduce unbind and rebind interfaces during usb reset > https://lists.ubuntu.com/archives/kernel-team/2014-April/042177.html > "If a driver claims additional interfaces, the > claim may fail because the old binding instance may still own the > additional interface when the new instance tries to claim it. " > > After usb_reset_device, the whole enumeration will run again, No, only part of the enumeration. The kernel does read the device and config descriptors again. But if the reset succeeded, the kernel doesn't carry out any of the other parts of enumeration. > why this > patch say the previous solution will be fail to claim additional > interface? Suppose a driver claims interfaces 0 and 1, and then they have to be unbound and rebound. The old code would unbind interface 0, then rebind it, then unbind interface 1, and then rebind it. Suppose the driver's probe routine for interface 0 tries to claim interface 1? The probe routine runs when interface 0 is rebound. At that time interface 1 hasn't been unbound yet. Since interface 1 is still owned, the driver will not be able to claim it. On the other hand, the new code will unbind interface 0, then unbind interface 1, then rebind interface 0, and then rebind interface 1. Now if the driver's probe routine for interface 0 tries to claim interface 1, the claim will succeed because interface has already been unbound. 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
