linux-kernel - [PATCH 3.12 138/142] Input: joydev - do not report stale values on first open

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Date:   Mon, 10 Apr 2017 17:33:39 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Raphael Assenat <raph@...hnet.net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Oliver Neukum <ONeukum@...e.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 138/142] Input: joydev - do not report stale values on first open

From: Raphael Assenat <raph@...hnet.net>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 45536d373a21d441bd488f618b6e3e9bfae839f3 upstream.

Postpone axis initialization to the first open instead of doing it
in joydev_connect. This is to make sure the generated startup events
are representative of the current joystick state rather than what
it was when joydev_connect() was called, potentially much earlier.
Once the first user is connected to joydev node we'll be updating
joydev->abs[] values and subsequent clients will be getting correct
initial states as well.

This solves issues with joystick driven menus that start scrolling
up each time they are started, until the user moves the joystick to
generate events. In emulator menu setups where the menu program is
restarted every time the game exits, the repeated need to move the
joystick to stop the unintended scrolling gets old rather quickly...

Signed-off-by: Raphael Assenat <raph@...hnet.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Oliver Neukum <ONeukum@...e.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/input/joydev.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c
index f362883c94e3..3736c1759524 100644
--- a/drivers/input/joydev.c
+++ b/drivers/input/joydev.c
@@ -188,6 +188,17 @@ static void joydev_detach_client(struct joydev *joydev,
 	synchronize_rcu();
 }
 
+static void joydev_refresh_state(struct joydev *joydev)
+{
+	struct input_dev *dev = joydev->handle.dev;
+	int i, val;
+
+	for (i = 0; i < joydev->nabs; i++) {
+		val = input_abs_get_val(dev, joydev->abspam[i]);
+		joydev->abs[i] = joydev_correct(val, &joydev->corr[i]);
+	}
+}
+
 static int joydev_open_device(struct joydev *joydev)
 {
 	int retval;
@@ -202,6 +213,8 @@ static int joydev_open_device(struct joydev *joydev)
 		retval = input_open_device(&joydev->handle);
 		if (retval)
 			joydev->open--;
+		else
+			joydev_refresh_state(joydev);
 	}
 
 	mutex_unlock(&joydev->mutex);
@@ -823,7 +836,6 @@ static int joydev_connect(struct input_handler *handler, struct input_dev *dev,
 		j = joydev->abspam[i];
 		if (input_abs_get_max(dev, j) == input_abs_get_min(dev, j)) {
 			joydev->corr[i].type = JS_CORR_NONE;
-			joydev->abs[i] = input_abs_get_val(dev, j);
 			continue;
 		}
 		joydev->corr[i].type = JS_CORR_BROKEN;
@@ -838,10 +850,6 @@ static int joydev_connect(struct input_handler *handler, struct input_dev *dev,
 		if (t) {
 			joydev->corr[i].coef[2] = (1 << 29) / t;
 			joydev->corr[i].coef[3] = (1 << 29) / t;
-
-			joydev->abs[i] =
-				joydev_correct(input_abs_get_val(dev, j),
-					       joydev->corr + i);
 		}
 	}
 
-- 
2.12.2