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 <dsd@laptop.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/mouse/synaptics.c

@@ -743,6 +743,11 @@ int synaptics_init(struct psmouse *psmouse)
 	return -1;
 }
 
+bool synaptics_supported(void)
+{
+	return true;
+}
+
 #else /* CONFIG_MOUSE_PS2_SYNAPTICS */
 
 void __init synaptics_module_init(void)
@@ -754,5 +759,10 @@ int synaptics_init(struct psmouse *psmouse)
 	return -ENOSYS;
 }
 
+bool synaptics_supported(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_MOUSE_PS2_SYNAPTICS */