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usb_ep_set_halt(9) [centos man page]

USB_EP_SET_HALT(9)					      Kernel Mode Gadget API						USB_EP_SET_HALT(9)

NAME
usb_ep_set_halt - sets the endpoint halt feature. SYNOPSIS
int usb_ep_set_halt(struct usb_ep * ep); ARGUMENTS
ep the non-isochronous endpoint being stalled DESCRIPTION
Use this to stall an endpoint, perhaps as an error report. Except for control endpoints, the endpoint stays halted (will not stream any data) until the host clears this feature; drivers may need to empty the endpoint's request queue first, to make sure no inappropriate transfers happen. Note that while an endpoint CLEAR_FEATURE will be invisible to the gadget driver, a SET_INTERFACE will not be. To reset endpoints for the current altsetting, see usb_ep_clear_halt. When switching altsettings, it's simplest to use usb_ep_enable or usb_ep_disable for the endpoints. Returns zero, or a negative error code. On success, this call sets underlying hardware state that blocks data transfers. Attempts to halt IN endpoints will fail (returning -EAGAIN) if any transfer requests are still queued, or if the controller hardware (usually a FIFO) still holds bytes that the host hasn't collected. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 USB_EP_SET_HALT(9)

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USB_EP_QUEUE(9) 					      Kernel Mode Gadget API						   USB_EP_QUEUE(9)

NAME
usb_ep_queue - queues (submits) an I/O request to an endpoint. SYNOPSIS
int usb_ep_queue(struct usb_ep * ep, struct usb_request * req, gfp_t gfp_flags); ARGUMENTS
ep the endpoint associated with the request req the request being submitted gfp_flags GFP_* flags to use in case the lower level driver couldn't pre-allocate all necessary memory with the request. DESCRIPTION
This tells the device controller to perform the specified request through that endpoint (reading or writing a buffer). When the request completes, including being canceled by usb_ep_dequeue, the request's completion routine is called to return the request to the driver. Any endpoint (except control endpoints like ep0) may have more than one transfer request queued; they complete in FIFO order. Once a gadget driver submits a request, that request may not be examined or modified until it is given back to that driver through the completion callback. Each request is turned into one or more packets. The controller driver never merges adjacent requests into the same packet. OUT transfers will sometimes use data that's already buffered in the hardware. Drivers can rely on the fact that the first byte of the request's buffer always corresponds to the first byte of some USB packet, for both IN and OUT transfers. Bulk endpoints can queue any amount of data; the transfer is packetized automatically. The last packet will be short if the request doesn't fill it out completely. Zero length packets (ZLPs) should be avoided in portable protocols since not all usb hardware can successfully handle zero length packets. (ZLPs may be explicitly written, and may be implicitly written if the request 'zero' flag is set.) Bulk endpoints may also be used for interrupt transfers; but the reverse is not true, and some endpoints won't support every interrupt transfer. (Such as 768 byte packets.) Interrupt-only endpoints are less functional than bulk endpoints, for example by not supporting queueing or not handling buffers that are larger than the endpoint's maxpacket size. They may also treat data toggle differently. Control endpoints ... after getting a setup callback, the driver queues one response (even if it would be zero length). That enables the status ack, after transferring data as specified in the response. Setup functions may return negative error codes to generate protocol stalls. (Note that some USB device controllers disallow protocol stall responses in some cases.) When control responses are deferred (the response is written after the setup callback returns), then usb_ep_set_halt may be used on ep0 to trigger protocol stalls. Depending on the controller, it may not be possible to trigger a status-stage protocol stall when the data stage is over, that is, from within the response's completion routine. For periodic endpoints, like interrupt or isochronous ones, the usb host arranges to poll once per interval, and the gadget driver usually will have queued some data to transfer at that time. Returns zero, or a negative error code. Endpoints that are not enabled report errors; errors will also be reported when the usb peripheral is disconnected. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 USB_EP_QUEUE(9)
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