522989a27c
When an isochronous transfer is enqueued, xhci_queue_isoc_tx_prepare() will ensure that there is enough room on the transfer rings for all of the isochronous TDs for that URB. However, when xhci_queue_isoc_tx() is enqueueing individual isoc TDs, the prepare_transfer() function can fail if the endpoint state has changed to disabled, error, or some other unknown state. With the current code, if Nth TD (not the first TD) fails, the ring is left in a sorry state. The partially enqueued TDs are left on the ring, and the first TRB of the TD is not given back to the hardware. The enqueue pointer is left on the TRB after the last successfully enqueued TD. This means the ring is basically useless. Any new transfers will be enqueued after the failed TDs, which the hardware will never read because the cycle bit indicates it does not own them. The ring will fill up with untransferred TDs, and the endpoint will be basically unusable. The untransferred TDs will also remain on the TD list. Since the td_list is a FIFO, this basically means the ring handler will be waiting on TDs that will never be completed (or worse, dereference memory that doesn't exist any more). Change the code to clean up the isochronous ring after a failed transfer. If the first TD failed, simply return and allow the xhci_urb_enqueue function to free the urb_priv. If the Nth TD failed, first remove the TDs from the td_list. Then convert the TRBs that were enqueued into No-op TRBs. Make sure to flip the cycle bit on all enqueued TRBs (including any link TRBs in the middle or between TDs), but leave the cycle bit of the first TRB (which will show software-owned) intact. Then move the ring enqueue pointer back to the first TRB and make sure to change the xhci_ring's cycle state to what is appropriate for that ring segment. This ensures that the No-op TRBs will be overwritten by subsequent TDs, and the hardware will not start executing random TRBs because the cycle bit was left as hardware-owned. This bug is unlikely to be hit, but it was something I noticed while tracking down the watchdog timer issue. I verified that the fix works by injecting some errors on the 250th isochronous URB queued, although I could not verify that the ring is in the correct state because uvcvideo refused to talk to the device after the first usb_submit_urb() failed. Ring debugging shows that the ring looks correct, however. 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: Andiry Xu <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 | ||
README
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.