[PATCH] input: Add support for Wacom protocol 4 serial tablets

[Hans de Goede <hdegoede@redhat.com>]

Hi All,

Recent version of xf86-input-wacom no longer support directly accessing
serial tablets. Instead xf86-input-wacom now expects all wacom tablets to
be driven by the kernel and to show up as evdev devices.

This has caused old serial Wacom tablets to stop working for people who still
have such tablets. Julian Squires has written a serio input driver to fix this:
https://github.com/tokenrove/wacom-serial-iv

About a year ago Julian submitted this upstream, back then the response by
Dmitry was:

> The driver looks quite reasonable, however that would be the 4th Wacom
> driver in the tree... I wonder if it is time to split out transport
> parts from core wacom functionality so that it can be shared by USB, I2C
> and serio devices.

I've taken a quick look at this, the i2c driver is for touchscreens and in
the protocol has nothing in common with the other wacom drivers. The w8001
driver is for serial touchscreens and again a completely different protocol.

The wacom usb driver already deals with what appears to be a lot of different
protocol nuances, see for example wacom_wac.c, and non of all the different
package formats parsed in wacom_wac.c seem to have anything in common with
the wacom protocol 4 spoken over serial. So it seems that there is nothing
to be shared since these are really significant different devices which happen
to be from the same vendor. Moreover the usb wacom bits are being reworked
to use hid instead of to more or less parse usb hid reports themselves, and
I certainly don't want this driver to get in the way of that.

So all in all I believe it is best to keep this as a standalone driver.

Hence I'm hereby re-submitting this driver for upstream inclusion.

This is a significantly cleaned up version of the driver initially submitted
by Julian, with improved Graphire support (I own an old Graphire myself).

Regards,

Hans