usb: misc: onboard_usb_hub: Add support for clock input

Most onboard USB hubs have a dedicated crystal oscillator but on some
boards the clock signal for the hub is provided by the SoC.

In order to support this, we add the possibility of specifying a
clock in the devicetree that gets enabled/disabled when the hub
is powered up/down.
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Link: https://lore.kernel.org/r/20231127112234.109073-2-frieder@fris.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/onboard_usb_hub.c

@@ -5,6 +5,7 @@
  * Copyright (c) 2022, Google LLC
  */
 
+#include <linux/clk.h>
 #include <linux/device.h>
 #include <linux/export.h>
 #include <linux/err.h>
@@ -61,12 +62,19 @@ struct onboard_hub {
 	bool going_away;
 	struct list_head udev_list;
 	struct mutex lock;
+	struct clk *clk;
 };
 
 static int onboard_hub_power_on(struct onboard_hub *hub)
 {
 	int err;
 
+	err = clk_prepare_enable(hub->clk);
+	if (err) {
+		dev_err(hub->dev, "failed to enable clock: %pe\n", ERR_PTR(err));
+		return err;
+	}
+
 	err = regulator_bulk_enable(hub->pdata->num_supplies, hub->supplies);
 	if (err) {
 		dev_err(hub->dev, "failed to enable supplies: %pe\n", ERR_PTR(err));
@@ -93,6 +101,8 @@ static int onboard_hub_power_off(struct onboard_hub *hub)
 		return err;
 	}
 
+	clk_disable_unprepare(hub->clk);
+
 	hub->is_powered_on = false;
 
 	return 0;
@@ -267,6 +277,10 @@ static int onboard_hub_probe(struct platform_device *pdev)
 		return err;
 	}
 
+	hub->clk = devm_clk_get_optional(dev, NULL);
+	if (IS_ERR(hub->clk))
+		return dev_err_probe(dev, PTR_ERR(hub->clk), "failed to get clock\n");
+
 	hub->reset_gpio = devm_gpiod_get_optional(dev, "reset",
 						  GPIOD_OUT_HIGH);
 	if (IS_ERR(hub->reset_gpio))