Documentation/usb/dwc3.txt

   1
   2  TODO
   3 ~~~~~~
   4 Please pick something while reading :)
   5
   6 - Implement streaming support for BULK endpoints
   7   Tatyana's patch "usb: Add streams support to the gadget framework"
   8   introduces streaming support for the gadget driver.
   9   Every usb_request has new field called stream_id which holds its id.
  10   Every usb_ep has a field num_supported_strms which describes the max
  11   number of streams supported (for this ep).
  12   UAS is AFAIK the only gadget with streaming support.
  13
  14 - Convert interrupt handler to per-ep-thread-irq
  15
  16   As it turns out some DWC3-commands ~1ms to complete. Currently we spin
  17   until the command completes which is bad.
  18
  19   Implementation idea:
  20   - dwc core implements a demultiplexing irq chip for interrupts per
  21     endpoint. The interrupt numbers are allocated during probe and belong
  22     to the device. If MSI provides per-endpoint interrupt this dummy
  23     interrupt chip can be replaced with "real" interrupts.
  24   - interrupts are requested / allocated on usb_ep_enable() and removed on
  25     usb_ep_disable(). Worst case are 32 interrupts, the lower limit is two
  26     for ep0/1.
  27   - dwc3_send_gadget_ep_cmd() will sleep in wait_for_completion_timeout()
  28     until the command completes.
  29   - the interrupt handler is split into the following pieces:
  30     - primary handler of the device
  31       goes through every event and calls generic_handle_irq() for event
  32       it. On return from generic_handle_irq() in acknowledges the event
  33       counter so interrupt goes away (eventually).
  34
  35     - threaded handler of the device
  36       none
  37
  38     - primary handler of the EP-interrupt
  39       reads the event and tries to process it. Everything that requries
  40       sleeping is handed over to the Thread. The event is saved in an
  41       per-endpoint data-structure.
  42       We probably have to pay attention not to process events once we
  43       handed something to thread so we don't process event X prio Y
  44       where X > Y.
  45
  46     - threaded handler of the EP-interrupt
  47       handles the remaining EP work which might sleep such as waiting
  48       for command completion.
  49
  50   Latency:
  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).