linux/Documentation/usb/dwc3.rst
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   1===========
   2DWC3 driver
   3===========
   4
   5
   6TODO
   7~~~~
   8
   9Please 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).
  54