diff options
Diffstat (limited to 'drivers/usb/core/urb.c')
| -rw-r--r-- | drivers/usb/core/urb.c | 29 |
1 files changed, 25 insertions, 4 deletions
diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c index 9d912bfdcffe..e0d9d948218c 100644 --- a/drivers/usb/core/urb.c +++ b/drivers/usb/core/urb.c @@ -214,9 +214,25 @@ EXPORT_SYMBOL_GPL(usb_unanchor_urb); * urb->interval is modified to reflect the actual transfer period used * (normally some power of two units). And for isochronous urbs, * urb->start_frame is modified to reflect when the URB's transfers were - * scheduled to start. Not all isochronous transfer scheduling policies - * will work, but most host controller drivers should easily handle ISO - * queues going from now until 10-200 msec into the future. + * scheduled to start. + * + * Not all isochronous transfer scheduling policies will work, but most + * host controller drivers should easily handle ISO queues going from now + * until 10-200 msec into the future. Drivers should try to keep at + * least one or two msec of data in the queue; many controllers require + * that new transfers start at least 1 msec in the future when they are + * added. If the driver is unable to keep up and the queue empties out, + * the behavior for new submissions is governed by the URB_ISO_ASAP flag. + * If the flag is set, or if the queue is idle, then the URB is always + * assigned to the first available (and not yet expired) slot in the + * endpoint's schedule. If the flag is not set and the queue is active + * then the URB is always assigned to the next slot in the schedule + * following the end of the endpoint's previous URB, even if that slot is + * in the past. When a packet is assigned in this way to a slot that has + * already expired, the packet is not transmitted and the corresponding + * usb_iso_packet_descriptor's status field will return -EXDEV. If this + * would happen to all the packets in the URB, submission fails with a + * -EXDEV error code. * * For control endpoints, the synchronous usb_control_msg() call is * often used (in non-interrupt context) instead of this call. @@ -305,8 +321,13 @@ int usb_submit_urb(struct urb *urb, gfp_t mem_flags) struct usb_host_endpoint *ep; int is_out; - if (!urb || urb->hcpriv || !urb->complete) + if (!urb || !urb->complete) return -EINVAL; + if (urb->hcpriv) { + WARN_ONCE(1, "URB %p submitted while active\n", urb); + return -EBUSY; + } + dev = urb->dev; if ((!dev) || (dev->state < USB_STATE_UNAUTHENTICATED)) return -ENODEV; |