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When the xHCI driver encounters a Missed Service Interval event for an
isochronous endpoint ring, it means the host controller skipped over
one or more isochronous TDs. For TD that is skipped, skip_isoc_td() is
called. This sets the frame descriptor status to -EXDEV, and also sets
the value stored in the int pointed to by status to -EXDEV.
If the isochronous TD happens to be the last TD in an URB,
handle_tx_event() will use the status variable to give back the URB to
the USB core. That means drivers will see urb->status as -EXDEV.
It turns out that EHCI, UHCI, and OHCI always set urb->status to zero for
an isochronous urb, regardless of what the frame status is. See
itd_complete() in ehci-sched.c:
} else {
/* URB was too late */
desc->status = -EXDEV;
}
}
/* handle completion now? */
if (likely ((urb_index + 1) != urb->number_of_packets))
goto done;
/* ASSERT: it's really the last itd for this urb
list_for_each_entry (itd, &stream->td_list, itd_list)
BUG_ON (itd->urb == urb);
*/
/* give urb back to the driver; completion often (re)submits */
dev = urb->dev;
ehci_urb_done(ehci, urb, 0);
ehci_urb_done() completes the URB with the status of the third argument, which
is always zero in this case.
It turns out that many USB webcam drivers, such as uvcvideo, cannot
handle urb->status set to a non-zero value. They will not resubmit
their isochronous URBs in that case, and userspace will see a frozen
video.
Change the xHCI driver to be consistent with the EHCI and UHCI driver,
and always set urb->status to 0 for isochronous URBs.
This patch should be backported to kernels as old as 2.6.36
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: "Xu, Andiry" <Andiry.Xu@amd.com>
Cc: stable@kernel.org
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| .. | ||
| atm | ||
| c67x00 | ||
| class | ||
| core | ||
| early | ||
| gadget | ||
| host | ||
| image | ||
| misc | ||
| mon | ||
| musb | ||
| otg | ||
| renesas_usbhs | ||
| serial | ||
| storage | ||
| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| usb-skeleton.c | ||
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("khubd").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.