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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
- 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.
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).
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