t5r2: explain what "T5R2" is
Thanks to seobrien@ for doing the research here. The Kernel patch that
adds T5R2 support [0] is also related, but didn't seem to have enough
relevant information to warrant including in a comment.
[0]: https://lore.kernel.org/lkml/1309324042-22943-8-git-send-email-djkurtz@chromium.org/t/
BUG=none
TEST=none
Change-Id: I8390d053f0c61f26fbde6f730193f92f174a1108
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/gestures/+/4013428
Commit-Queue: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Torsha Banerjee <torsha@google.com>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
Reviewed-by: Denis Brockus <dbrockus@chromium.org>
Auto-Submit: Harry Cutts <hcutts@chromium.org>
Tested-by: Harry Cutts <hcutts@chromium.org>
diff --git a/include/gestures.h b/include/gestures.h
index 720517b..3f747dd 100644
--- a/include/gestures.h
+++ b/include/gestures.h
@@ -55,6 +55,10 @@
float orientation_maximum;
unsigned short max_finger_cnt; // Max finger slots in one report
unsigned short max_touch_cnt; // Max fingers that can be detected at once
+
+ // Whether this is a "Track 5, Report 2" touchpad, which can track up to five
+ // fingers but only report the locations of two. (For more details, see
+ // https://crrev.com/37cccb42e652b50f9e788d90e82252f78c78f1ed)
unsigned supports_t5r2:1;
unsigned support_semi_mt:1;
unsigned is_button_pad:1;
diff --git a/include/t5r2_correcting_filter_interpreter.h b/include/t5r2_correcting_filter_interpreter.h
index 06daf55..5c010a5 100644
--- a/include/t5r2_correcting_filter_interpreter.h
+++ b/include/t5r2_correcting_filter_interpreter.h
@@ -12,6 +12,11 @@
namespace gestures {
+// T5R2 ("Track 5, Report 2") is an approach used by some old touchpads which
+// can track up to five fingers but only report the locations of two of them.
+// (See https://crrev.com/37cccb42e652b50f9e788d90e82252f78c78f1ed for more
+// details.)
+//
// This interpreter corrects some T5R2 HardwareState structures. It
// has been noticed that in some cases, fingers are removed from the
// touchpad but, a HardwareState with touch_cnt set to 0 is never
