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