rtc: sun6i: Enable the bus clock when provided

H6 and newer variants of the RTC hardware have a bus clock gate in the
PRCM CCU. This was not known at the time H6 support was added, so it was
not included in the H6 RTC binding, nor in the H6 PRCM CCU driver. Now
that this clock gate is documented, it is included in the A100 and D1
PRCM CCU drivers. Therefore, the RTC driver needs to have a consumer for
the clock gate to prevent Linux from disabling it.

Patch-changes: 3
 - New patch for compatibility with new CCU drivers
Signed-off-by: NSamuel Holland <samuel@sholland.org>
Reviewed-by: NMaxime Ripard <maxime@cerno.tech>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220203021736.13434-4-samuel@sholland.org

drivers/rtc/rtc-sun6i.c

@@ -668,11 +668,35 @@ static int sun6i_rtc_resume(struct device *dev)
 static SIMPLE_DEV_PM_OPS(sun6i_rtc_pm_ops,
 	sun6i_rtc_suspend, sun6i_rtc_resume);
 
+static void sun6i_rtc_bus_clk_cleanup(void *data)
+{
+	struct clk *bus_clk = data;
+
+	clk_disable_unprepare(bus_clk);
+}
+
 static int sun6i_rtc_probe(struct platform_device *pdev)
 {
 	struct sun6i_rtc_dev *chip = sun6i_rtc;
+	struct device *dev = &pdev->dev;
+	struct clk *bus_clk;
 	int ret;
 
+	bus_clk = devm_clk_get_optional(dev, "bus");
+	if (IS_ERR(bus_clk))
+		return PTR_ERR(bus_clk);
+
+	if (bus_clk) {
+		ret = clk_prepare_enable(bus_clk);
+		if (ret)
+			return ret;
+
+		ret = devm_add_action_or_reset(dev, sun6i_rtc_bus_clk_cleanup,
+					       bus_clk);
+		if (ret)
+			return ret;
+	}
+
 	if (!chip) {
 		chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL);
 		if (!chip)