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path: root/drivers/usb/core/urb.c
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Diffstat (limited to 'drivers/usb/core/urb.c')
-rw-r--r--drivers/usb/core/urb.c29
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;