The USB 3.0 bus specification added an "Endpoint Companion" descriptor that is
supposed to follow all SuperSpeed Endpoint descriptors. This descriptor is used
to extend the bus protocol to allow more packets to be sent to an endpoint per
"microframe". The word microframe was removed from the USB 3.0 specification
because the host controller does not send Start Of Frame (SOF) symbols down the
USB 3.0 wires.
The descriptor defines a bMaxBurst field, which indicates the number of packets
of wMaxPacketSize that a SuperSpeed device can send or recieve in a service
interval. All non-control endpoints may set this value as high as 16 packets
(bMaxBurst = 15).
The descriptor also allows isochronous endpoints to further specify that they
can send and receive multiple bursts per service interval. The bmAttributes
allows them to specify a "Mult" of up to 3 (bmAttributes = 2).
Bulk endpoints use bmAttributes to report the number of "Streams" they support.
This was an extension of the endpoint pipe concept to allow multiple mass
storage device commands to be outstanding for one bulk endpoint at a time. This
should allow USB 3.0 mass storage devices to support SCSI command queueing.
Bulk endpoints can say they support up to 2^16 (65,536) streams.
The information in the endpoint companion descriptor must be stored with the
other device, config, interface, and endpoint descriptors because the host
controller needs to access them quickly, and we need to install some default
values if a SuperSpeed device doesn't provide an endpoint companion descriptor.
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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