libpayload: usb: Add interval attribute to endpoints

Read bInterval from endpoint descriptors and store it in our endpoint_t
struct. The interval is encoded dependently on the device' speed and the
endpoint's type. Therefore, it will be normalized to the binary logarithm
of the number of microframes, i.e.
  t = 125us * 2^interval

The interval attribute will be used in the xHCI driver.

Original-Change-Id: I65a8eda6145faf34666800789f0292e640a8141b
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: http://review.coreboot.org/3449
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
(cherry picked from commit aee44fa37d780cfec95c444f43defd89ded021f0)

BUG=chrome-os-partner:21969
TEST=None

Change-Id: Ic42ad3c193390d5838b563346604b1ef9f385b52
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/168094
2 files changed