path: root/Documentation/usb/dwc3.txt
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-Please pick something while reading :)
-- Convert interrupt handler to per-ep-thread-irq
- As it turns out some DWC3-commands ~1ms to complete. Currently we spin
- until the command completes which is bad.
- Implementation idea:
- - dwc core implements a demultiplexing irq chip for interrupts per
- endpoint. The interrupt numbers are allocated during probe and belong
- to the device. If MSI provides per-endpoint interrupt this dummy
- interrupt chip can be replaced with "real" interrupts.
- - interrupts are requested / allocated on usb_ep_enable() and removed on
- usb_ep_disable(). Worst case are 32 interrupts, the lower limit is two
- for ep0/1.
- - dwc3_send_gadget_ep_cmd() will sleep in wait_for_completion_timeout()
- until the command completes.
- - the interrupt handler is split into the following pieces:
- - primary handler of the device
- goes through every event and calls generic_handle_irq() for event
- it. On return from generic_handle_irq() in acknowledges the event
- counter so interrupt goes away (eventually).
- - threaded handler of the device
- none
- - primary handler of the EP-interrupt
- reads the event and tries to process it. Everything that requires
- sleeping is handed over to the Thread. The event is saved in an
- per-endpoint data-structure.
- We probably have to pay attention not to process events once we
- handed something to thread so we don't process event X prio Y
- where X > Y.
- - threaded handler of the EP-interrupt
- handles the remaining EP work which might sleep such as waiting
- for command completion.
- Latency:
- There should be no increase in latency since the interrupt-thread has a
- high priority and will be run before an average task in user land
- (except the user changed priorities).