usb: usb5303: add support for reference clock specified in device tree

USB3503 chip supports 8 values of reference clock. The value is
specified by REF_SEL[1:0] pins and INT_N line. This patch add support
for getting 'refclk' clock, enabling it and setting INT_N line according
to the value of the gathered clock. If no clock has been specified,
driver defaults to the old behaviour (assuming that clock has been
specified by REF_SEL pins from primary reference clock frequencies
table).

Signed-off-by: Marek Szyprowski <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/usb/usb3503.txt

···
 - reset-gpios: Should specify GPIO for reset.
 - initial-mode: Should specify initial mode.
                 (1 for HUB mode, 2 for STANDBY mode)
+- refclk: Clock used for driving REFCLK signal (optional, if not provided
+	the driver assumes that clock signal is always available, its
+	rate is specified by REF_SEL pins and a value from the primary
+	reference clock frequencies table is used)
+- refclk-frequency: Frequency of the REFCLK signal as defined by REF_SEL
+	pins (optional, if not provided, driver will not set rate of the
+	REFCLK signal and assume that a value from the primary reference
+	clock frequencies table is used)
 
 Examples:
 	usb3503@08 {

drivers/usb/misc/usb3503.c

···
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
+#include <linux/clk.h>
 #include <linux/i2c.h>
 #include <linux/gpio.h>
 #include <linux/delay.h>
···
 	enum usb3503_mode	mode;
 	struct regmap		*regmap;
 	struct device		*dev;
+	struct clk		*clk;
 	u8	port_off_mask;
 	int	gpio_intn;
 	int	gpio_reset;
 	int	gpio_connect;
+	bool	secondary_ref_clk;
 };
 
 static int usb3503_reset(struct usb3503 *hub, int state)
···
 		hub->gpio_reset		= pdata->gpio_reset;
 		hub->mode		= pdata->initial_mode;
 	} else if (np) {
+		struct clk *clk;
 		hub->port_off_mask = 0;
+
+		clk = devm_clk_get(dev, "refclk");
+		if (IS_ERR(clk) && PTR_ERR(clk) != -ENOENT) {
+			dev_err(dev, "unable to request refclk (%d)\n", err);
+			return PTR_ERR(clk);
+		}
+
+		if (!IS_ERR(clk)) {
+			u32 rate = 0;
+			hub->clk = clk;
+
+			if (!of_property_read_u32(np, "refclk-frequency",
+						 &rate)) {
+
+				switch (rate) {
+				case 38400000:
+				case 26000000:
+				case 19200000:
+				case 12000000:
+					hub->secondary_ref_clk = 0;
+					break;
+				case 24000000:
+				case 27000000:
+				case 25000000:
+				case 50000000:
+					hub->secondary_ref_clk = 1;
+					break;
+				default:
+					dev_err(dev,
+						"unsupported reference clock rate (%d)\n",
+						(int) rate);
+					return -EINVAL;
+				}
+				err = clk_set_rate(hub->clk, rate);
+				if (err) {
+					dev_err(dev,
+						"unable to set reference clock rate to %d\n",
+						(int) rate);
+					return err;
+				}
+			}
+
+			err = clk_prepare_enable(hub->clk);
+			if (err) {
+				dev_err(dev,
+					"unable to enable reference clock\n");
+				return err;
+			}
+		}
 
 		property = of_get_property(np, "disabled-ports", &len);
 		if (property && (len / sizeof(u32)) > 0) {
···
 		dev_err(dev, "Ports disabled with no control interface\n");
 
 	if (gpio_is_valid(hub->gpio_intn)) {
-		err = devm_gpio_request_one(dev, hub->gpio_intn,
-				GPIOF_OUT_INIT_HIGH, "usb3503 intn");
+		int val = hub->secondary_ref_clk ? GPIOF_OUT_INIT_LOW :
+						   GPIOF_OUT_INIT_HIGH;
+		err = devm_gpio_request_one(dev, hub->gpio_intn, val,
+					    "usb3503 intn");
 		if (err) {
 			dev_err(dev,
 				"unable to request GPIO %d as connect pin (%d)\n",