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To calculate the TD size for a particular TRB in an isoc TD, we need know the endpoint's max packet size. Isochronous endpoints also encode the number of additional service opportunities in their wMaxPacketSize field. The TD size calculation did not mask off those bits before using the field. This resulted in incorrect TD size information for isochronous TRBs when an URB frame buffer crossed a 64KB boundary. For example: - an isoc endpoint has 2 additional service opportunites and a max packet size of 1020 bytes - a frame transfer buffer contains 3060 bytes - one frame buffer crosses a 64KB boundary, and must be split into one 1276 byte TRB, and one 1784 byte TRB. The TD size is is the number of packets that remain to be transferred for a TD after processing all the max packet sized packets in the current TRB and all previous TRBs. For this TD, the number of packets to be transferred is (3060 / 1020), or 3. The first TRB contains 1276 bytes, which means it contains one full packet, and a 256 byte remainder. After processing all the max packet-sized packets in the first TRB, the host will have 2 packets left to transfer. The old code would calculate the TD size for the first TRB as: total packet count = DIV_ROUND_UP (TD length / endpoint wMaxPacketSize) total packet count - (first TRB length / endpoint wMaxPacketSize) The math should have been: total packet count = DIV_ROUND_UP (3060 / 1020) = 3 3 - (1276 / 1020) = 2 Since the old code didn't mask off the additional service interval bits from the wMaxPacketSize field, the math ended up as total packet count = DIV_ROUND_UP (3060 / 5116) = 1 1 - (1276 / 5116) = 1 Fix this by masking off the number of additional service opportunities in the wMaxPacketSize field. This patch should be backported to stable kernels as old as 3.0, that contain the commit 4da6e6f247a2601ab9f1e63424e4d944ed4124f3 "xhci 1.0: Update TD size field format." It may not apply well to kernels older than 3.2 because of commit 29cc88979a8818cd8c5019426e945aed118b400e "USB: use usb_endpoint_maxp() instead of le16_to_cpu()". Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: stable@vger.kernel.org
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.