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commit1530bbc627upstream. Sergio reported that when he recorded audio from a USB headset mic plugged into the USB 3.0 port on his ASUS N53SV-DH72, the audio sounded "robotic". When plugged into the USB 2.0 port under EHCI on the same laptop, the audio sounded fine. The device is: Bus 002 Device 004: ID 046d:0a0c Logitech, Inc. Clear Chat Comfort USB Headset The problem was tracked down to the Fresco Logic xHCI host controller not correctly reporting short transfers on isochronous IN endpoints. The driver would submit a 96 byte transfer, the device would only send 88 or 90 bytes, and the xHCI host would report the transfer had a "successful" completion code, with an untransferred buffer length of 8 or 6 bytes. The successful completion code and non-zero untransferred length is a contradiction. The xHCI host is supposed to only mark a transfer as successful if all the bytes are transferred. Otherwise, the transfer should be marked with a short packet completion code. Without the EHCI bus trace, we wouldn't know whether the xHCI driver should trust the completion code or the untransferred length. With it, we know to trust the untransferred length. Add a new xHCI quirk for the Fresco Logic host controller. If a transfer is reported as successful, but the untransferred length is non-zero, print a warning. For the Fresco Logic host, change the completion code to COMP_SHORT_TX and process the transfer like a short transfer. This should be backported to stable kernels that contain the commitf5182b4155"xhci: Disable MSI for some Fresco Logic hosts." That commit was marked for stable kernels as old as 2.6.36. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Reported-by: Sergio Correia <lists@uece.net> Tested-by: Sergio Correia <lists@uece.net> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.