Input: psmouse - fix Synaptics detection when protocol is disabled

For configurations where Synaptics hardware is present but the Synaptics
extensions support is not compiled in, the mouse is reprobed and a new
device is allocated on every suspend/resume.

During probe, psmouse_switch_protocol() calls psmouse_extensions() with
set_properties=1. This calls the dummy synaptics_init() which returns an
error code, instructing us not to use the synaptics extensions.

During resume, psmouse_reconnect() calls psmouse_extensions() with
set_properties=0, in which case call to synaptics_init() is bypassed and
PSMOUSE_SYNAPTICS is returned. Since the result is different from previous
attempt psmouse_reconnect() fails and full re-probe happens.

Fix this by tweaking the set_properties=0 codepath in psmouse_extensions()
to be more careful about offering PSMOUSE_SYNAPTICS extensions.

Signed-off-by: Daniel Drake <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/mouse/psmouse-base.c

···
 		synaptics_hardware = true;
 
 		if (max_proto > PSMOUSE_IMEX) {
-			if (!set_properties || synaptics_init(psmouse) == 0)
+/*
+ * Try activating protocol, but check if support is enabled first, since
+ * we try detecting Synaptics even when protocol is disabled.
+ */
+			if (synaptics_supported() &&
+			    (!set_properties || synaptics_init(psmouse) == 0)) {
 				return PSMOUSE_SYNAPTICS;
+			}
+
 /*
  * Some Synaptics touchpads can emulate extended protocols (like IMPS/2).
  * Unfortunately Logitech/Genius probes confuse some firmware versions so

drivers/input/mouse/synaptics.c

···
 	return -1;
 }
 
+bool synaptics_supported(void)
+{
+	return true;
+}
+
 #else /* CONFIG_MOUSE_PS2_SYNAPTICS */
 
 void __init synaptics_module_init(void)
···
 int synaptics_init(struct psmouse *psmouse)
 {
 	return -ENOSYS;
+}
+
+bool synaptics_supported(void)
+{
+	return false;
 }
 
 #endif /* CONFIG_MOUSE_PS2_SYNAPTICS */

drivers/input/mouse/synaptics.h

···
 int synaptics_detect(struct psmouse *psmouse, bool set_properties);
 int synaptics_init(struct psmouse *psmouse);
 void synaptics_reset(struct psmouse *psmouse);
+bool synaptics_supported(void);
 
 #endif /* _SYNAPTICS_H */