drm/radeon: only add the mm i2c bus if the hw_i2c module param is set

commit 46783150 upstream.

It seems it can corrupt the monitor EDID in certain cases on certain
boards when running sensors detect.  It's rarely used anyway outside
of AIW boards.

http://lists.lm-sensors.org/pipermail/lm-sensors/2012-April/035847.html
http://lists.freedesktop.org/archives/xorg/2011-January/052239.htmlSigned-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/radeon/radeon_i2c.c

@@ -898,6 +898,10 @@ struct radeon_i2c_chan *radeon_i2c_create(struct drm_device *dev,
 	struct radeon_i2c_chan *i2c;
 	int ret;
 
+	/* don't add the mm_i2c bus unless hw_i2c is enabled */
+	if (rec->mm_i2c && (radeon_hw_i2c == 0))
+		return NULL;
+
 	i2c = kzalloc(sizeof(struct radeon_i2c_chan), GFP_KERNEL);
 	if (i2c == NULL)
 		return NULL;