mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-01-13 00:29:50 +00:00
831abf7664
Trying to read data from the Pegasus Technologies NoteTaker (0e20:0101) [1] with the Windows App (EasyNote) works natively but fails when Windows is running under KVM (and the USB device handed to KVM). The reason is a USB control message usb 4-2.2: control urb: bRequestType=22 bRequest=09 wValue=0200 wIndex=0001 wLength=0008 This goes to endpoint address 0x01 (wIndex); however, endpoint address 0x01 does not exist. There is an endpoint 0x81 though (same number, but other direction); the app may have meant that endpoint instead. The kernel thus rejects the IO and thus we see the failure. Apparently, Linux is more strict here than Windows ... we can't change the Win app easily, so that's a problem. It seems that the Win app/driver is buggy here and the driver does not behave fully according to the USB HID class spec that it claims to belong to. The device seems to happily deal with that though (and seems to not really care about this value much). So the question is whether the Linux kernel should filter here. Rejecting has the risk that somewhat non-compliant userspace apps/ drivers (most likely in a virtual machine) are prevented from working. Not rejecting has the risk of confusing an overly sensitive device with such a transfer. Given the fact that Windows does not filter it makes this risk rather small though. The patch makes the kernel more tolerant: If the endpoint address in wIndex does not exist, but an endpoint with toggled direction bit does, it will let the transfer through. (It does NOT change the message.) With attached patch, the app in Windows in KVM works. usb 4-2.2: check_ctrlrecip: process 13073 (qemu-kvm) requesting ep 01 but needs 81 I suspect this will mostly affect apps in virtual environments; as on Linux the apps would have been adapted to the stricter handling of the kernel. I have done that for mine[2]. [1] http://www.pegatech.com/ [2] https://sourceforge.net/projects/notetakerpen/ Signed-off-by: Kurt Garloff <kurt@garloff.de> Acked-by: Alan Stern <stern@rowland.harvard.edu> Cc: stable <stable@vger.kernel.org> 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.