Re: [PATCH v3] bcm5974: Set BUTTONPAD property

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

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
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.

INPUT_PROP_POINTER:

This property indicates that the device is not transposed on the screen
and thus requires use of an on-screen pointer to trace user's movements.
Typical pointer devices: touchpads, tablets, mice; non-pointer device:
touchscreen.

How does this sound?

Thanks.

-- 
Dmitry