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