linux-kernel - Re: [PATCH v4] HID: hid-multitouch: support fine-grain orientation reporting

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Message-ID: <20171011204324.GA24245@mars.bitmath.org>
Date:   Wed, 11 Oct 2017 22:43:24 +0200
From:   Henrik Rydberg <rydberg@...math.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Dmitry Torokhov <dtor@...omium.org>,
        Wei-Ning Huang <wnhuang@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Input <linux-input@...r.kernel.org>,
        Peter Hutterer <peter.hutterer@...-t.net>
Subject: Re: [PATCH v4] HID: hid-multitouch: support fine-grain orientation
 reporting

> > > , but I'd go for fixing the documentation. And re-reading it, it's not 
> > > clear that the doc tells us to have [0,90]. It mentions negative values 
> > > and out of ranges too, so we might just as well simply clarify that we 
> > > rather have [-90,90], with 0 being "north".
> > 
> > ... I'd like the documentation fix to go in together in one go with this 
> > patch if possible.
> > 
> 
> Sounds like a plan.

How about this patch?

Henrik

---

>From b14f92066dfab3f8a255ec7b5a30cb1a864dc62f Mon Sep 17 00:00:00 2001
From: Henrik Rydberg <rydberg@...math.org>
Date: Wed, 11 Oct 2017 22:41:39 +0200
Subject: [PATCH] Input: docs - clarify the usage of ABS_MT_ORIENTATION

As more drivers start to support touch orientation, clarify how the
value range should be set to match the expected behavior in
userland.

Signed-off-by: Henrik Rydberg <rydberg@...math.org>
---
 Documentation/input/multi-touch-protocol.rst | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/Documentation/input/multi-touch-protocol.rst b/Documentation/input/multi-touch-protocol.rst
index 8035868..a0c5c03 100644
--- a/Documentation/input/multi-touch-protocol.rst
+++ b/Documentation/input/multi-touch-protocol.rst
@@ -269,15 +269,17 @@ ABS_MT_ORIENTATION
     The orientation of the touching ellipse. The value should describe a signed
     quarter of a revolution clockwise around the touch center. The signed value
     range is arbitrary, but zero should be returned for an ellipse aligned with
-    the Y axis of the surface, a negative value when the ellipse is turned to
-    the left, and a positive value when the ellipse is turned to the
-    right. When completely aligned with the X axis, the range max should be
-    returned.
+    the Y axis of the surface (north). A negative value should be returned when
+    the ellipse is turned to the left (west), with the smallest value reported
+    when aligned with the negative X axis. The largest value should be returned
+    when aligned with the positive X axis.
+
+    The value range should be specified as [-range_max, range_max].
 
     Touch ellipsis are symmetrical by default. For devices capable of true 360
-    degree orientation, the reported orientation must exceed the range max to
+    degree orientation, the reported orientation will exceed range_max, in order to
     indicate more than a quarter of a revolution. For an upside-down finger,
-    range max * 2 should be returned.
+    +- 2 * range_max should be returned.
 
     Orientation can be omitted if the touch area is circular, or if the
     information is not available in the kernel driver. Partial orientation
-- 
2.14.1