• Dan Williams's avatar
    usb: xhci: change enumeration scheme to 'new scheme' by default · 48fc7dbd
    Dan Williams authored
    Change the default enumeration scheme for xhci attached non-SuperSpeed
    devices from:
    
       Reset
       SetAddress [xhci address-device BSR = 0]
       GetDescriptor(8)
       GetDescriptor(18)
    
    ...to:
    
       Reset
       [xhci address-device BSR = 1]
       GetDescriptor(64)
       Reset
       SetAddress [xhci address-device BSR = 0]
       GetDescriptor(18)
    
    ...as some devices misbehave when encountering a SetAddress command
    prior to GetDescriptor.  There are known legacy devices that require
    this scheme, but testing has found at least one USB3 device that fails
    enumeration when presented with this ordering.  For now, follow the ehci
    case and enable 'new scheme' by default for non-SuperSpeed devices.
    
    To support this enumeration scheme on xhci the AddressDevice operation
    needs to be performed twice.  The first instance of the command enables
    the HC's device and slot context info for the device, but omits sending
    the device a SetAddress command (BSR == block set address request).
    Then, after GetDescriptor completes, follow up with the full
    AddressDevice+SetAddress operation.
    
    As mentioned before, this ordering of events with USB3 devices causes an
    extra state transition to be exposed to xhci.  Previously USB3 devices
    would transition directly from 'enabled' to 'addressed' and never need
    to underrun responses to 'get descriptor'. We do see the 64-byte
    descriptor fetch the correct data, but the following 18-byte descriptor
    read after the reset gets:
    
    bLength            = 0
    bDescriptorType    = 0
    bcdUSB             = 0
    bDeviceClass       = 0
    bDeviceSubClass    = 0
    bDeviceProtocol    = 0
    bMaxPacketSize0    = 9
    
    instead of:
    
    bLength            = 12
    bDescriptorType    = 1
    bcdUSB             = 300
    bDeviceClass       = 0
    bDeviceSubClass    = 0
    bDeviceProtocol    = 0
    bMaxPacketSize0    = 9
    
    which results in the discovery process looping until falling back to
    'old scheme' enumeration.
    Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
    Reported-by: default avatarDavid Moore <david.moore@gmail.com>
    Suggested-by: default avatarSarah Sharp <sarah.a.sharp@linux.intel.com>
    Reported-by: default avatarDan Carpenter <dan.carpenter@oracle.com>
    Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
    Signed-off-by: default avatarSarah Sharp <sarah.a.sharp@linux.intel.com>
    48fc7dbd
xhci-pci.c 11.6 KB