misc: atmel_pwm: add deferred-probing support

Two drivers (atmel-pwm-bl and leds-atmel-pwm) currently depend on the
atmel_pwm driver to have bound to any pwm-device before their devices
are probed.

Support deferred probing of such devices by making sure to return
-EPROBE_DEFER from pwm_channel_alloc when no pwm-device has yet been
bound.
Signed-off-by: NJohan Hovold <jhovold@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/atmel_pwm.c

@@ -90,8 +90,10 @@ int pwm_channel_alloc(int index, struct pwm_channel *ch)
 	unsigned long	flags;
 	int		status = 0;
 
-	/* insist on PWM init, with this signal pinned out */
-	if (!pwm || !(pwm->mask & 1 << index))
+	if (!pwm)
+		return -EPROBE_DEFER;
+
+	if (!(pwm->mask & 1 << index))
 		return -ENODEV;
 
 	if (index < 0 || index >= PWM_NCHAN || !ch)