On 08/18/2011 04:28 AM, Daniel Kurtz wrote: > Synaptics image sensor touchpads track 5 fingers, but only report 2. > This patch attempts to deal with some idiosyncrasies of these touchpads: > > * When there are 3 or more fingers, only two are reported. > * The touchpad tracks the 5 fingers in slot[0] through slot[4]. > * It always reports the lowest and highest valid slots in SGM and AGM > packets, respectively. > * The number of fingers is only reported in the SGM packet. However, > the number of fingers can change either before or after an AGM > packet. > * Thus, if an SGM reports a different number of fingers than the last > SGM, it is impossible to tell whether the intervening AGM corresponds > to the old number of fingers or the new number of fingers. > * For example, when going from 2->3 fingers, it is not possible to tell > whether tell AGM contains slot[1] (old 2nd finger) or slot[2] (new > 3rd finger). > * When fingers are added one at at time, from 1->2->3, it is possible to > track which slots are contained in the SGM and AGM packets: > 1 finger: SGM = slot[0], no AGM > 2 fingers: SGM = slot[0], AGM = slot[1] > 3 fingers: SGM = slot[0], AGM = slot[2] > * It is also possible to track which slot is contained in the SGM when 1 > of 2 fingers is removed. This is because the touchpad sends a special > (0,0,0) AGM packet whenever all fingers are removed except slot[0]: > Last AGM == (0,0,0): SGM contains slot[1] > Else: SGM contains slot[0] > * However, once there are 3 fingers, if exactly 1 finger is removed, it > is impossible to tell which 2 slots are contained in SGM and AGM. > The (SGM,AGM) could be (0,1), (0,2), or (1,2). There is no way to know. > * Similarly, if two fingers are simultaneously removed (3->1), then it > is only possible to know if SGM still contains slot[0]. > * Since it is not possible to reliably track which slot is being > reported, we invalidate the tracking_id every time the number of > fingers changes until this ambiguity is resolved when: > a) All fingers are removed. > b) 4 or 5 fingers are touched, generates an AGM-CONTACT packet. > c) All fingers are removed except slot[0]. In this special case, the > ambiguity is resolved since by the (0,0,0) AGM packet. > > Behavior of the driver: > > When 2 or more fingers are present on the touchpad, the kernel reports > up to two MT-B slots containing the position data for two of the fingers > reported by the touchpad. If the identity of a finger cannot be tracked > when the number-of-fingers changes, the corresponding MT-B slot will be > invalidated (track_id set to -1), and a new track_id will be assigned in > a subsequent input event report. > > The driver always reports the total number of fingers using one of the > EV_KEY/BTN_TOOL_*TAP events. This could differ from the number of valid > MT-B slots for two reasons: > a) There are more than 2 fingers on the pad. > b) During ambiguous number-of-fingers transitions, the correct track_id > for one or both of the slots cannot be determined, so the slots are > invalidated. > > Thus, this is a hybrid singletouch/MT-B scheme. Userspace can detect > this behavior by noting that the driver supports more EV_KEY/BTN_TOOL_*TAP > events than its maximum EV_ABS/ABS_MT_SLOT. > > Signed-off-by: Daniel Kurtz <djkurtz@xxxxxxxxxxxx> Acked-by: Chase Douglas <chase.douglas@xxxxxxxxxxxxx> -- 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
