linux-kernel - [PATCH] driver/input/ff-memless.c

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Date:	Mon, 7 Dec 2009 14:37:30 -0500
From:	Gary Stein <lordcnidarian@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] driver/input/ff-memless.c

I was experiencing force feedback joystick issues in my Force 3D Pro and
when developing a new driver for the new Logitech G940 after I
recompiled my kernel.

I was able to track it down to a signed vs unsigned problem in
ff-memless.c and gcc 4.4.2.
The code in question did not seem to give a problem with gcc 4.2.4.

According to gitweb, a signed vs unsigned was changed on May 8th by
Jussi Kivilinna <jussi.kivilinna@...et.fi>
Input: ff-memless - fix signed to unsigned bit overflow

to change the gain from a signed to an unsigned int to fix a rumble
issue, but it appears to broke a the
constant force section of the code.

It is a simple, cast to fix and should not have any ill effects.

gary


--- linux-2.6.31.orig/drivers/input/ff-memless.c	2009-09-09
17:13:59.000000000 -0500
+++ linux-2.6.31.int/drivers/input/ff-memless.c	2009-12-07
15:09:22.000000000 -0500
@@ -239,8 +239,8 @@
 		level = fixp_new16(apply_envelope(state,
 					new->u.constant.level,
 					&new->u.constant.envelope));
-		x = fixp_mult(fixp_sin(i), level) * gain / 0xffff;
-		y = fixp_mult(-fixp_cos(i), level) * gain / 0xffff;
+		x = (int)(fixp_mult(fixp_sin(i), level) * gain) / 0xffff;
+		y = (int)(fixp_mult(-fixp_cos(i), level) * gain) / 0xffff;
 		/*
 		 * here we abuse ff_ramp to hold x and y of constant force
 		 * If in future any driver wants something else than x and y
--
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