clk: sunxi: Add a dummy clock driver for the RTC

The 32kHz clock ("LOSC") on sunxi SoCs is provided by the RTC. It is
used, among other things, by the XHCI controller in the H6. To be able
to call clk_get_bulk() on the XHCI controller, some device needs to
provide all referenced clocks.

Since LOSC is a fixed-rate always-on clock, implementation is trivial.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/drivers/clk/sunxi/clk_sun6i_rtc.c b/drivers/clk/sunxi/clk_sun6i_rtc.c
new file mode 100644
index 0000000..0c280d2
--- /dev/null
+++ b/drivers/clk/sunxi/clk_sun6i_rtc.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright (C) 2018 Amarula Solutions.
+ * Copyright (C) 2020 Samuel Holland <samuel@sholland.org>
+ */
+
+#include <clk-uclass.h>
+#include <dm.h>
+
+static int clk_sun6i_rtc_enable(struct clk *clk)
+{
+	return 0;
+}
+
+static const struct clk_ops clk_sun6i_rtc_ops = {
+	.enable = clk_sun6i_rtc_enable,
+};
+
+static const struct udevice_id sun6i_rtc_ids[] = {
+	{ .compatible = "allwinner,sun6i-a31-rtc" },
+	{ .compatible = "allwinner,sun8i-a23-rtc" },
+	{ .compatible = "allwinner,sun8i-h3-rtc" },
+	{ .compatible = "allwinner,sun8i-r40-rtc" },
+	{ .compatible = "allwinner,sun8i-v3-rtc" },
+	{ .compatible = "allwinner,sun50i-h5-rtc" },
+	{ .compatible = "allwinner,sun50i-h6-rtc" },
+	{ }
+};
+
+U_BOOT_DRIVER(clk_sun6i_rtc) = {
+	.name		= "clk_sun6i_rtc",
+	.id		= UCLASS_CLK,
+	.of_match	= sun6i_rtc_ids,
+	.ops		= &clk_sun6i_rtc_ops,
+};