rtc: rv8803: add wakeup-source support

The RV8803 can be wired directly to a PMIC that can wake up an SoC without
the CPU getting interrupts.

Link: https://lore.kernel.org/r/20240108004357.602918-1-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/epson,rx8900.yaml

@@ -29,6 +29,8 @@ properties:
 
   trickle-diode-disable: true
 
+  wakeup-source: true
+
 required:
   - compatible
   - reg

drivers/rtc/rtc-rv8803.c

@@ -712,9 +712,12 @@ static int rv8803_probe(struct i2c_client *client)
 			if (err)
 				dev_err(&client->dev, "failed to set wake IRQ\n");
 		}
+	} else {
+		if (device_property_read_bool(&client->dev, "wakeup-source"))
+			device_init_wakeup(&client->dev, true);
+		else
+			clear_bit(RTC_FEATURE_ALARM, rv8803->rtc->features);
 	}
-	if (!client->irq)
-		clear_bit(RTC_FEATURE_ALARM, rv8803->rtc->features);
 
 	if (of_property_read_bool(client->dev.of_node, "epson,vdet-disable"))
 		rv8803->backup |= RX8900_FLAG_VDETOFF;