clk: bcm: rpi: Allow the driver to be probed by DT

The current firmware clock driver for the RaspberryPi can only be probed by
manually registering an associated platform_device.

While this works fine for cpufreq where the device gets attached a clkdev
lookup, it would be tedious to maintain a table of all the devices using
one of the clocks exposed by the firmware.

Since the DT on the other hand is the perfect place to store those
associations, make the firmware clocks driver probe-able through the device
tree so that we can represent it as a node.

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: linux-clk@vger.kernel.org
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/cb8203b862e386ac6c3df3eff0bb5a238b6ec97a.1592210452.git-series.maxime@cerno.techSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/bcm/clk-raspberrypi.c

@@ -255,8 +255,16 @@ static int raspberrypi_clk_probe(struct platform_device *pdev)
 	struct raspberrypi_clk *rpi;
 	int ret;
 
-	firmware_node = of_find_compatible_node(NULL, NULL,
-					"raspberrypi,bcm2835-firmware");
+	/*
+	 * We can be probed either through the an old-fashioned
+	 * platform device registration or through a DT node that is a
+	 * child of the firmware node. Handle both cases.
+	 */
+	if (dev->of_node)
+		firmware_node = of_get_parent(dev->of_node);
+	else
+		firmware_node = of_find_compatible_node(NULL, NULL,
+							"raspberrypi,bcm2835-firmware");
 	if (!firmware_node) {
 		dev_err(dev, "Missing firmware node\n");
 		return -ENOENT;
@@ -300,9 +308,16 @@ static int raspberrypi_clk_remove(struct platform_device *pdev)
 	return 0;
 }
 
+static const struct of_device_id raspberrypi_clk_match[] = {
+	{ .compatible = "raspberrypi,firmware-clocks" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, raspberrypi_clk_match);
+
 static struct platform_driver raspberrypi_clk_driver = {
 	.driver = {
 		.name = "raspberrypi-clk",
+		.of_match_table = raspberrypi_clk_match,
 	},
 	.probe          = raspberrypi_clk_probe,
 	.remove		= raspberrypi_clk_remove,