Re: tablet udev rules (was Re: Getting up/down events working on Bamboo touchpad)

Ron,

You are right.  We discussed this issue before.  Wacom doesn't have a
serial number to distinguish tablets of the same model in the
firmware.  I like your by-path rule.  But I need to test it a bit more
to see how reliable it is.  I'll get back to you later.

Ping

On 7/10/07, Ron <ron@xxxxxxxxxx> wrote:
> On Mon, Jul 09, 2007 at 03:09:34PM -0700, Ping@LinuxWacom wrote:
> > Both of your suggestions in the OS level help linuxwacom users, that
> > is for sure.  My concern is how do we deal with a system with 2
> > identical tablets.  I know users running 2 Cintiq 21 UX to gain full
> > accuracy and flexibility. Right now, the system has trouble to tell
> > which Cintiq is the first monitor when the system wakes up from a
> > sleep or even a nap :).  Do you guys have any suggestion?
>
> I thought we'd got stuck without a good answer to this previously.
> The full thread is at:
> http://sourceforge.net/mailarchive/message.php?msg_name=20060418020303.GA16999%40hank.shelbyville.oz
>
> But the main bits of note to this question were me wondering:
>
>  if there is a serial number or other unique id in the tablet that
>  we can access, then we can always make a <TabletType>-<SerialNum>
>  link or similar that people could use.
>
> To which you confirmed:
>
>  As a short reply to the following discussion, there is no tablet
>  specific id to distinguish tablets of the same model and size.
>
>
> So at this stage, the only method I'm aware of that we could use
> to distinguish two identical devices reliably would be to use the
> /dev/input/by-path links to differentiate them by the usb port
> they are plugged into (since that's really the only thing the
> machine can know about them that is different but potentially
> stable).
>
> They aren't the most user friendly invention in the world, and
> will need to be configured for each individual user, but for a
> static workstation where the tablets are plugged in once and
> left that way, they should always give the same unique device
> name for each tablet.  Its just a bit brittle if you start
> moving things about and has a small initial hand-hack burden.
>
>
> But I guess if we can't convince the hardware crew to add a unique
> identifier of some sort to new tablets (and even if we could, that
> doesn't help anyone today), then we'll just need to make the by-path
> configuration more friendly to users somehow...
>
> hmm.
>
> We should be able to concoct a reasonable by-path rule specific
> to wacom devices that auto-configuration tools can fairly easily
> pattern match, but which will remain the same until the device
> is moved to a different port...
>
> It will probably depend on a relatively recent udev, but starting
> from the set of rules I posted earlier, try something like:
>
> ----- psuedo patch ----
>  # Convenience link for the common case of a single tablet.
>  KERNEL=="event[0-9]*", SYSFS{idVendor}=="056a", SYMLINK="input/wacom"
>
> + # You probably won't need this IMPORT rule, since an earlier file is
> + # likely to have already done it, but the rule that follows it does
> + # depend on that having happened to set ID_PATH.
> + # IMPORT{program}="path_id %p"
> +
> + # Port specific link for users of multiple tablets of the same type.
> + KERNEL=="event[0-9]*", SYSFS{idVendor}=="056a", ENV{ID_PATH}=="?*", 
> SYMLINK+="input/by-path/$env{ID_PATH}-wacom"
>
>  # Type-named links for multiple tablets.  If you want to use multiple
> -----------------------
>
> Here this gives me (for one tablet):
> /dev/input/by-path/pci-0000:00:02.0-usb-0:4:1.0-wacom -> ../event4
> /dev/input/by-path/pci-0000:00:02.1-usb-0:4:1.0-wacom -> ../event4
>
> ... when I plug it into two different usb ports.  Should work much
> the same if you try it with two tablets.  If nobody here can get it
> to wreck their system then I can include something like it for the
> next upload.
>
> It's not a great answer, but it adds a constant factor to the device
> name that should survive a simple suspend or reboot reliably enough,
> and lets people search for *-wacom instead of having to figure out
> which *-event devices they want from that lot -- which is a bit more
> friendly than having the entire name be like black magic to them...
>
> If anyone can think of a better way to do this I'd love to hear it.
>
> Cheers,
> Ron

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