Whiskers: Increase size threshold for palms

The touch size reported by the whiskers touchpad increases as more
fingers are added. As a result, when there are four fingers they are
often incorrectly classified as palms. This CL drastically increases the
palm detection threshold for touch size when there are multiple fingers,
relying only on pressure for palm detection in those cases.

TEST=Replay feedback reports complaining about missed gestures with new
config: Gestures are detected correctly.
Perform manual testing to check for correct detection of 1-4 fingers
with and without a palm present.

Change-Id: I9b64f0082fedf934b51da2f8e09b7eefe80ec438
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/xorg-conf/+/2068521
Tested-by: Sean O'Brien <seobrien@chromium.org>
Reviewed-by: Harry Cutts <hcutts@chromium.org>
Commit-Queue: Sean O'Brien <seobrien@chromium.org>
diff --git a/40-touchpad-cmt.conf b/40-touchpad-cmt.conf
index 01fd9fd..4df97fd 100644
--- a/40-touchpad-cmt.conf
+++ b/40-touchpad-cmt.conf
@@ -292,6 +292,10 @@
     Option          "Palm Filter Top Edge Enable" "1"
     Option          "Smooth Accel" "1"
     Option          "Tap Minimum Pressure" "20.0"
+    # Touch size increases with finger count, so ignore touch size for
+    # detecting palms if there are multiple touches.
+    Option          "Multiple Palm Width" "200.0"
 Section "InputClass"