evdev: support for touchscreens not providing BTN_TOUCH
jacmet at sunsite.dk
Mon May 23 00:11:52 PDT 2011
>>>>> "Peter" == Peter Hutterer <peter.hutterer at who-t.net> writes:
>> Notice that this touchscreen works out of the box on Windows without
>> any custom driver (just the standard HID).
Peter> We've had a discussion about this in September at a MT workshop
Peter> and it's a bit of a weak argument. AIUI, companies don't get the
Peter> Win7 stamp of approval if it doesn't work with the standard HID
Peter> driver. And my guess is that the standard HID driver is all but
Peter> standard but merely the HID driver forward-ported from Win(n-1),
Peter> including several quirks that have been there in the past -
Peter> because removing those would break support for older devices.
Peter> So we don't know what the windows standard HID driver does but
Peter> we do know that companies are unlikely to sell devices that
Peter> don't work against that driver. so standard HID is defined as
Peter> "whatever Win7 accepts".
Indeed. The fact that it works on Windows doesn't mean that it follows
the HID standard completely/correctly. Nevertheless, reality trumps
theory, and we have lots of cases where we tweak the Linux kernel
behaviour to better match Windows to get devices to work (E.G. all the
Peter> Really, hearing a sentence along the line of "we don't know what
Peter> this HID field is for either but we use it this way and Win7
Peter> accepts it" from a HW person was quite interesting.
>> Peter, would you accept a patch doing that?
Peter> yes, I think the best solution here would be to compare rel and
Peter> abs axes and prioritise the axes that have x/y over the ones
Peter> that don't. which is a general issue with evdev, the rel vs abs
Peter> check is a bit too coarse. there are axes that are more
Peter> important than others.
Great, I'll try to cook up a patch.
Bye, Peter Korsgaard
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