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    SubjectRe: [PATCH 1/1]: input: add support for VirtualBox touchscreen emulation to the Lifebook driver
    On Tue, Feb 23, 2010 at 09:55:33PM +0100, Michael Thayer wrote:
    > Hello Dmitry,
    > Thanks for your comments!
    > Le mardi 23 février 2010 à 09:58 -0800, Dmitry Torokhov a écrit :
    > > On Tue, Feb 23, 2010 at 12:13:35PM +0100, Michael Thayer wrote:
    > > > This patch adds support for VirtualBox touchscreen emulation to the Lifebook
    > > > input driver.
    > [snip]
    > > I am wondering if it is a good idea to piggy-back on Lifebook. The
    > > devices are sufficiently different with Lifebook really having 2
    > > separate devices (touchscreen and either regular external mouse or a
    > > touchpad) and VirtualBox having asingle device that looks like a pointer
    > > (not a touchscreen since pointer moves constantly, not while "touching")
    > > with absolute coordinates reporting.
    > I'm not sure, if we ended up doing a completely new device, how different it
    > would end up being. Emulating a touchscreen or a tablet makes sense for us as
    > these are both something known, which will work with existing systems without
    > too much tweaking (I could imagine us adding Solaris support at a later point,
    > and it would be nice to see "little" OSes picking up support independently).

    But the virtual mouse is not a touchscreen or a tablet, it behaves

    > The two devices also make sense for us on the one hand because xf86-input-evdev
    > currently only understands absolute devices without mouse buttons

    Hmm, I scanned through it and I did not see anything specifically
    removing mouse buttons from absolute devices there... Is it still valid
    for the recent version of evdev driver?

    > (yes I know,
    > we could send them patches too if we had too, but we would rather not patch the
    > whole world :) ) and on the other because it makes it easy for us to switch
    > between absolute and relative event reporting, which is a big plus.

    Why is this a big plus? Also, can't evdev handle devices reporting both
    relative and absolute events?

    > Of course,
    > as you point out, we have the unused touch bit, but the device works nicely
    > sending co-ordinates without "touching", and having at least nominal touch
    > functionality is rather a prerequisite for emulating a touch screen.

    You are relying on the fact that currently userspace components rely on
    drivers not sending coordinates data without touch; as soon as userspace
    (evdev) starts validating it and ignoring coordinate events without
    ABS_PRESSURE or BTN_TOUCH you'll be toast.

    > > I think it would be better if we had separate protocol module for that.
    > > [snip]
    > Separate module as in separate driver, or changes to the actual (PS/2 extension)
    > protocol? If the second, then what did you have in mind?

    First, create a separate protocol handler (module similar to
    lifebook.c), allocate protocol number, something like PSMOUSE_VBPS, and
    plumb it into psmouse-base.c in the same fashion othe protocol handlers
    do it.

    > One protocol change
    > I could think of, other than the thing with the buttons, would be a magic knock
    > rather than DMI matching, as that would let others piggy-back on us. Not a big
    > advantage for us of course, but it might be one for you.

    I'd rather you stick with DMI, piggybackers can simply add their DMI
    strings. The reason I do not want to have magic knock is that it may
    disturb real hardware probing which is already quite fragile.

    > > This issue should be fixed in the recent kernels.
    > Ah, I failed to see that (I was working against the Ubuntu Lucid kernel
    > after checking that there were no more recent changes to lifebook.c).
    > Is the fix in psmouse-base.c?

    Among others.

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