Documentation/usb/dwc3.rst

   1 ===========
   2 DWC3 driver
   3 ===========
   4
   5
   6 TODO
   7 ~~~~
   8
   9 Please pick something while reading :)
  10
  11 - Convert interrupt handler to per-ep-thread-irq
  12
  13   As it turns out some DWC3-commands ~1ms to complete. Currently we spin
  14   until the command completes which is bad.
  15
  16   Implementation idea:
  17
  18   - dwc core implements a demultiplexing irq chip for interrupts per
  19     endpoint. The interrupt numbers are allocated during probe and belong
  20     to the device. If MSI provides per-endpoint interrupt this dummy
  21     interrupt chip can be replaced with "real" interrupts.
  22   - interrupts are requested / allocated on usb_ep_enable() and removed on
  23     usb_ep_disable(). Worst case are 32 interrupts, the lower limit is two
  24     for ep0/1.
  25   - dwc3_send_gadget_ep_cmd() will sleep in wait_for_completion_timeout()
  26     until the command completes.
  27   - the interrupt handler is split into the following pieces:
  28
  29     - primary handler of the device
  30       goes through every event and calls generic_handle_irq() for event
  31       it. On return from generic_handle_irq() in acknowledges the event
  32       counter so interrupt goes away (eventually).
  33
  34     - threaded handler of the device
  35       none
  36
  37     - primary handler of the EP-interrupt
  38       reads the event and tries to process it. Everything that requires
  39       sleeping is handed over to the Thread. The event is saved in an
  40       per-endpoint data-structure.
  41       We probably have to pay attention not to process events once we
  42       handed something to thread so we don't process event X prio Y
  43       where X > Y.
  44
  45     - threaded handler of the EP-interrupt
  46       handles the remaining EP work which might sleep such as waiting
  47       for command completion.
  48
  49   Latency:
  50
  51    There should be no increase in latency since the interrupt-thread has a
  52    high priority and will be run before an average task in user land
  53    (except the user changed priorities).