On Tue, Jan 17, 2012 at 10:24:25AM -0800, Jason Gerecke wrote:
> On Tue, Jan 17, 2012 at 10:06 AM, Dmitry Torokhov
> <dmitry.torokhov@xxxxxxxxx> wrote:
> > On Thu, Jan 12, 2012 at 11:19:40AM +0100, Chase Douglas wrote:
> >> On 01/12/2012 01:22 AM, Henrik Rydberg wrote:
> >> >> Here's what I believe the meanings should be:
> >> >>
> >> >> Touchpad: pointer, !direct
> >> >> Touchscreen: !pointer, direct
> >> >> Drawing tablet: pointer, direct
> >> >> Magic mouse-like devices: !pointer, !direct
> >> >
> >> > Yes, this is what everyone is saying, except !pointer && !direct means
> >> > "default" or "figure it out some other way".
> >> >
> >> >> However, there is a further problem in that we can't easily support
> >> >> multiple tools with different behavior on the same evdev device. What
> >> >> would you say a bamboo touch+pen is, which I believe is used as an
> >> >> indirect device for touch but a direct device for tools. Thus, in the
> >> >> thread I linked from back in September, Henrik and I agreed that direct
> >> >> should only apply when the tool is touch, and pointer should apply for
> >> >> all other tools. This would result in the following:
> >> >
> >> > To try to move back to a sane track, try this, where the word "apply"
> >> > in the previous paragraph has been changed to "care" instead:
> >>
> >> I am still having trouble understanding what you are saying. If I
> >> literally try to insert "care" into the paragraph, I am confused because
> >> it's not quite correct grammar. I'm really trying to understand though.
> >> Also, maybe a better term than "don't care" is "not applicable"?
> >>
> >> It would help me most if you could explicitly provide your own
> >> definition of the properties.
> >>
> >> >> Touchpad: !pointer, !direct
> >> >
> >> > pointer && !direct, since pointer is "dont care".
> >>
> >> Here you say !direct if "don't care".
> >>
> >> >> Touchscreen: !pointer, direct
> >> >
> >> > Yes, !pointer && direct.
> >> >
> >> >> Drawing tablet (no touch): pointer, !direct
> >> >
> >> > pointer && direct, but the tool is not touch, so direct is "dont care".
> >>
> >> Here you say direct if "don't care".
> >>
> >> Why the difference?
> >>
> >> >> Pen+touch tablet: pointer, direct
> >> >
> >> > Yes, pointer && direct
> >> >
> >> >> Magic mouse-like devices: !pointer, !direct
> >> >
> >> > Both pointer and direct are "dont care", and the device needs to be
> >> > detected some other way. If there ever will be a special driver for
> >> > magic-mouse-like devices, using both relative pointer and touch data,
> >> > it will make sense to add a special property for such devices.
> >>
> >> Right now we are missing a property for a magic-mouse like device. It's
> >> valid to have neither direct nor pointer set from kernels 2.6.38 through
> >> 3.2 (at least).
> >>
> >> > Hopefully the above is showing clearly that what was "documented" in
> >> > the threads enclosing the protocol patches still holds, and that there
> >> > is no use to dwell on it further.
> >> >
> >> >> The properties weren't documented when they were merged, and they
> >> >> obviously aren't clear. However, if either table above is correct, then
> >> >> we can't assume that !pointer && !direct means "unknown".
> >> >
> >> > If all devices fell in the pointer or direct or both categories, we
> >> > could. If not all devices do, the problem is rather that some property
> >> > bits are missing (or excluded) from the description.
> >>
> >> Given my last statement above, we have a problem because previously
> >> released kernels are reporting the magic mouse correctly, and yet we
> >> still can't distinguish it from another device that merely does not have
> >> the property bits set. This is the crux of the issue as I see it. We
> >> cannot differentiate between "unknown" and a specific type of device
> >> given the interfaces from 2.6.38 through 3.2.
> >>
> >> >> There is a way to fix this in a backwards compatible way: add a new
> >> >> property bit called something like "PROPERTIES_AVAILABLE". If any bits
> >> >> are set, then it implies that the properties are available (which covers
> >> >> older kernels). If no bits are set, then the properties are unknown.
> >> >> What do you think?
> >> >
> >> > It is rather the special properties of the magic mouse that are
> >> > missing. All types of devices do not _have_ to use properties; most
> >> > types can be figured out by other means.
> >> >
> >> > Saying "prop == 0" is equivalent to "figure out some other way" makes
> >> > sense, but it is also sensible to say "(prop & some_subclass_of_bits)
> >> > == 0", since some properties are bound to describe totally different
> >> > things. This is what we did with "!direct && !pointer".
> >>
> >> This may work, but we need to document the classes. The next time any
> >> properties are added the documentation must be included :).
> >>
> >> >>> The same is applicable to other properties as well. If device is telling
> >> >>> you that it is a "buttonpad" you can trust it, but if it does not you
> >> >>> need to decide for yourself how to treat it.
> >> >
> >> > Yes, and this will always be true. Old devices or systems that become
> >> > used in new ways cannot always adapt to a "if property not present
> >> > then dont use that way" policy.
> >> >
> >> >> No, in kernels previous to 2.6.38 it's clearly unknown. My problem is
> >> >> that I believe there was no way to determine unknown properties. If
> >> >> unknown properties is equivalent to magic-mouse like devices, then we're
> >> >> going to treat a lot of devices wrong. Or, we have to use heuristics to
> >> >> determine what a device is, like no properties and MT and REL_{X,Y} ==
> >> >> magic-mouse like. Properties was supposed to resolve this once and for
> >> >> all, so we didn't need heuristics.
> >> >
> >> > Properties were added to be able to distinguish usecases that could
> >> > not be distinguished at all before. It was never meant to replace
> >> > everything else.
> >>
> >> Why shouldn't we use it for that? The code in evdev for determining the
> >> type of device is just a big hack. We'll obviously need it for a while
> >> since we don't have all drivers with all necessary properties set, but
> >> it seems a waste to have the interface and not fully use it.
> >>
> >> >>>> Henrik, can you comment on the documentation patches? You wrote the
> >> >>>> patch, so you hopefully know what's going on :).
> >> >
> >> > I wasn't copied in on the conversation, but they seem fairly well
> >> > commented on already.
> >>
> >> It's still not clear to me what the definitions are. It seems it won't
> >> be clear until either you or Dmitry give your own definitions in an
> >> explicit manner (something that could be copied into the formal
> >> documentation). Please help me out :).
> >>
> >
> > OK, so how about this:
> >
> > INPUT_PROP_DIRECT:
> >
> > This property idicates that device coordinates can be directly mapped to
> "Can", or "should"? A number of touchpads "can" be directly mapped,
> but aren't because it goes against the user's expectation.
"Can". The property bits are advisory; IIRC there were discussed a few
potential uses of input devices that would go against their "normal"
properties. However we are aiming at providing hints to userspace to
support auto-configuration for standard uses.
>
> > screen coordinates (not taking into account trivial transformations,
> > such as scaling, flipping and rotating). Non-direct input devices
> > require non-trivial transformation, such as absolute to relative
> > transformation for touchpads. Typical direct input devices:
> > touchscreens, drawing tablets; non-direct devices: touchpads, mice.
> This doesn't match what the wacom driver already exposes. Display
> tablets set the DIRECT bit, but non-display tablets do not.
Then wacom driver should be adjusted so we are consistent.
--
Dmitry
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