Monday, June 10, 2013

Amulet with the Linux Wacom driver under sub v3.8 kernel

Amulet are a great company - I believe their KVM-over-IP extender to be MUCH better than Avocent, AdderLink and ThinkLogical's offerings, but like everyone else, once you packetise up DVI and USB and send it over a network you are going to have to deal with funny effects of devices and drivers that play fast & lose with the specifications. This is from their engineering team;

Wacom tablet and Red Hat Linux has been traced to a bug in the Red Hat Linux Wacom driver. The driver has a very obvious bug in it whereby outward data is declared as inward. The Wacom tablet simply ignores this when it is connected directly, although this works it is actually because the tablet USB stack is sloppy. The rack card however cannot ignore anything else we wouldn’t be able to operate at all so it believes what the Red Hat driver is saying and waits for an event which then never happens.

As detailed below in our analysis of the Red Hat and main Linux code drivers this issue has been resolved in the latest Linux build, with the fix implementing exactly what we would expect to see. This however has not yet found its way in to Red Hat, although may do so later this year, again as per the details below.

To enable use of the Wacom tablet on the current version of Red Hat (5.3) you are using we have added a work around to the rack card firmware. It appears to work but will require testing in the lab  over the next couple of next week before we can release. The workaround has to circumvent many checks in the code that are designed to catch driver bugs just like this. As a result the workaround is very specific to Wacom devices and this exact bug so we can’t guarantee it will work if anything changes.

Red Hat 6.3 (Amulet Hotkey test version)
  • Red Hat version - Red Hat 6.3 (Santiago)
  • Kernel version - 2.6.32-279.el6.x86_64
  • RPM package - 2.6.32-279.el6.x86_64
  • Wacom driver source - wacom_sys.c
  • Driver bug - Incorrect bitmask causing incorrect data direction expectation in USB driver.
Code copied below shows the addition of the correct bit mask command (in red) in the latest Linux driver

Red Hat 5.3 (Client version)

Although versions numbers differ to Amulet Hotkey test version the Wacom driver is the same and has the same bug present
  • Latest Red Hat release (6.4)
  • RPM package - kernel-2.6.32-358.el6
  • Wacom driver source - wacom_sys.c
  • Driver bug - Still present as per RPM package 2.6.32-279.el6.x86_64

Main Linux code base
  • Version - v3.2.45
  • Driver bug - Present
  • Version - v3.3
  • Driver bug - Resolved
Future Red Hat 

  • Wikipedia gives the time frame for the next major RHL release (7.x) as Q3/4 2013
  • We can't be sure whether this would incorporate the fix to the Wacom driver however Wikipedia states "Red Hat Enterprise Linux 7 (?), 2013-6+ Will be based on Fedora 18,[17] which as of March 2013 uses Linux kernel 3.8.[18]". This would indicate that the upcoming release of Red Hat 7 will fix the issue, as it will use a newer kernel, v3.8

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