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Documentation / usb / dwc3.txt

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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

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