From ecefae6db042283bf88ef3777f2381b18df8ed46 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Tue, 18 Jun 2019 18:05:38 -0300 Subject: 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 Acked-by: Johan Hovold Acked-by: Felipe Balbi Signed-off-by: Greg Kroah-Hartman --- Documentation/usb/dwc3.rst | 53 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 Documentation/usb/dwc3.rst (limited to 'Documentation/usb/dwc3.rst') diff --git a/Documentation/usb/dwc3.rst b/Documentation/usb/dwc3.rst new file mode 100644 index 000000000000..f94a7ba16573 --- /dev/null +++ b/Documentation/usb/dwc3.rst @@ -0,0 +1,53 @@ +=========== +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). -- cgit v1.2.3