linux/Documentation/usb/dwc3.rst
Mauro Carvalho Chehab ecefae6db0 docs: usb: rename files to .rst and add them to drivers-api
While there are a mix of things here, most of the stuff
were written from Kernel developer's PoV. So, add them to
the driver-api book.

A follow up for this patch would be to move documents from
there that are specific to sysadmins, adding them to the
admin-guide.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Johan Hovold <johan@kernel.org>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-20 14:28:36 +02:00

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===========
DWC3 driver
===========
TODO
~~~~
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).