usb: add helper to extract bits 12:11 of wMaxPacketSize
commit 541b6fe63023f3059cf85d47ff2767a3e42a8e44 upstream.
According to USB Specification 2.0 table 9-4,
wMaxPacketSize is a bitfield. Endpoint's maxpacket
is laid out in bits 10:0. For high-speed,
high-bandwidth isochronous endpoints, bits 12:11
contain a multiplier to tell us how many
transactions we want to try per uframe.
This means that if we want an isochronous endpoint
to issue 3 transfers of 1024 bytes per uframe,
wMaxPacketSize should contain the value:
1024 | (2 << 11)
or 5120 (0x1400). In order to make Host and
Peripheral controller drivers' life easier, we're
adding a helper which returns bits 12:11. Note that
no care is made WRT to checking endpoint type and
gadget's speed. That's left for drivers to handle.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed