On Mon, Jun 04, 2018 at 10:42:31PM +0200, Benjamin Tissoires wrote: > On Mon, Jun 4, 2018 at 7:33 PM, Dmitry Torokhov > <dmitry.torokhov@xxxxxxxxx> wrote: > > On Mon, Jun 04, 2018 at 03:18:12PM +0200, Benjamin Tissoires wrote: > >> On Fri, Jun 1, 2018 at 8:43 PM, Dmitry Torokhov > >> <dmitry.torokhov@xxxxxxxxx> wrote: > >> > On Fri, Jun 01, 2018 at 04:16:09PM +0200, Benjamin Tissoires wrote: > >> >> On Fri, Aug 11, 2017 at 2:44 AM, Dmitry Torokhov > >> >> <dmitry.torokhov@xxxxxxxxx> wrote: > >> >> > According to Microsoft specification [1] for Precision Touchpads (and > >> >> > Touchscreens) the devices use "confidence" reports to signal accidental > >> >> > touches, or contacts that are "too large to be a finger". Instead of > >> >> > simply marking contact inactive in this case (which causes issues if > >> >> > contact was originally proper and we lost confidence in it later, as > >> >> > this results in accidental clicks, drags, etc), let's report such > >> >> > contacts as MT_TOOL_PALM and let userspace decide what to do. > >> >> > Additionally, let's report contact size for such touches as maximum > >> >> > allowed for major/minor, which should help userspace that is not yet > >> >> > aware of MT_TOOL_PALM to still perform palm rejection. > >> >> > > >> >> > An additional complication, is that some firmwares do not report > >> >> > non-confident touches as active. To cope with this we delay release of > >> >> > such contact (i.e. if contact was active we first report it as still > >> >> > active MT+TOOL_PALM and then synthesize the release event in a separate > >> >> > frame). > >> >> > >> >> I am not sure I agree with this part. The spec says that "Once a > >> >> device has determined that a contact is unintentional, it should clear > >> >> the confidence bit for that contact report and all subsequent > >> >> reports." > >> >> So in theory the spec says that if a touch has been detected as a > >> >> palm, the flow of events should not stop (tested on the PTP of the > >> >> Dell XPS 9360). > >> >> > >> >> However, I interpret a firmware that send (confidence 1, tip switch 1) > >> >> and then (confidence 0, tip switch 0) a simple release, and the > >> >> confidence bit should not be relayed. > >> > > >> > This unfortunately leads to false clicks: you start with finger, so > >> > confidence is 1, then you transition the same touch to palm (use your > >> > thumb and "roll" your hand until heel of it comes into contact with the > >> > screen). The firmware reports "no-confidence" and "release" in the same > >> > report and userspace seeing release does not pay attention to confidence > >> > (i.e. it does exactly "simple release" logic) and this results in UI > >> > interpreting this as a click. With splitting no-confidence > >> > (MT_TOOL_PALM) and release event into separate frames we help userspace > >> > to recognize that the contact should be discarded. > >> > >> After further thoughts, I would consider this to be a firmware bug, > >> and not how the firmware is supposed to be reporting palm. > >> For the precision touchpads, the spec says that the device "should > >> clear the confidence bit for that contact report and all subsequent > >> reports.". And it is how the Dell device I have here reports palms. > >> The firmware is not supposed to cut the event stream. > >> > >> There is a test for that: > >> https://docs.microsoft.com/en-us/previous-versions/windows/hardware/hck/dn456905%28v%3dvs.85%29 > >> which tells me that I am right here for PTP. > >> > >> The touchscreen spec is blurrier however. > > > > OK, that is great to know. > > > >> > >> > > >> >> > >> >> Do you have any precise example of reports where you need that feature? > >> > > >> > It was observed on Pixelbooks which use Wacom digitizers IIRC. > >> > >> Pixelbooks + Wacom means that it was likely a touchscreen. I am right > >> guessing the device did not went through Microsoft certification > >> process? > > > > That would be correct ;) At least the firmware that is shipping with > > Pixlebooks hasn't, I do now if anyone else sourced these Wacom parts for > > their MSWin devices. > > > >> > >> I am in favor of splitting the patch in 2. One for the generic > >> processing of confidence bit, and one for this spurious release. For > >> the spurious release, I'm more in favor of explicitly quirking the > >> devices in need of such quirk. > > > > Hmm, I am not sure about having specific quirk. It will be hard for > > users to accurately diagnose the issue if firmware is broken in this way > > so we could add a new quirk for a new device. > > One thing we can do is keep the quirked mechanism as default in > hid-multitouch, but remove it in hid-core. If people need the quirk, > they can just use hid-multitouch instead (talking about the long run > here). Hmm, I am confused. My patch did not touch hid-core or hid-input, only hid-multitouch... So we are already doing what you are proposing?.. > > However, I really believe this might only be required for a handful of > devices, and probably only touchscreens. So I would be tempted to not > make it default and see how many bug reports we have. Up to you but it is hard to detect for users. If just sometimes there are stray clicks... Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
