usb: common: introduce of_usb_get_maximum_speed()

this helper will be used for controllers which
want to work at a lower speed even though they
support higher USB transfer rates.

One such case is Texas Instruments' AM437x
SoC where it uses a USB3 controller without
a USB3 PHY, rendering the controller USB2-only.

Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 38 insertions, 11 deletions

diff --git a/drivers/usb/usb-common.c b/drivers/usb/usb-common.c
index 675384dabfe9..d771870a819e 100644
--- a/drivers/usb/usb-common.c
+++ b/drivers/usb/usb-common.c
@@ -43,20 +43,20 @@ const char *usb_otg_state_string(enum usb_otg_state state)
 }
 EXPORT_SYMBOL_GPL(usb_otg_state_string);
 
+static const char *const speed_names[] = {
+	[USB_SPEED_UNKNOWN] = "UNKNOWN",
+	[USB_SPEED_LOW] = "low-speed",
+	[USB_SPEED_FULL] = "full-speed",
+	[USB_SPEED_HIGH] = "high-speed",
+	[USB_SPEED_WIRELESS] = "wireless",
+	[USB_SPEED_SUPER] = "super-speed",
+};
+
 const char *usb_speed_string(enum usb_device_speed speed)
 {
-	static const char *const names[] = {
-		[USB_SPEED_UNKNOWN] = "UNKNOWN",
-		[USB_SPEED_LOW] = "low-speed",
-		[USB_SPEED_FULL] = "full-speed",
-		[USB_SPEED_HIGH] = "high-speed",
-		[USB_SPEED_WIRELESS] = "wireless",
-		[USB_SPEED_SUPER] = "super-speed",
-	};
-
-	if (speed < 0 || speed >= ARRAY_SIZE(names))
+	if (speed < 0 || speed >= ARRAY_SIZE(speed_names))
 		speed = USB_SPEED_UNKNOWN;
-	return names[speed];
+	return speed_names[speed];
 }
 EXPORT_SYMBOL_GPL(usb_speed_string);
 
@@ -112,6 +112,33 @@ enum usb_dr_mode of_usb_get_dr_mode(struct device_node *np)
 	return USB_DR_MODE_UNKNOWN;
 }
 EXPORT_SYMBOL_GPL(of_usb_get_dr_mode);
+
+/**
+ * of_usb_get_maximum_speed - Get maximum requested speed for a given USB
+ * controller.
+ * @np: Pointer to the given device_node
+ *
+ * The function gets the maximum speed string from property "maximum-speed",
+ * and returns the corresponding enum usb_device_speed.
+ */
+enum usb_device_speed of_usb_get_maximum_speed(struct device_node *np)
+{
+	const char *maximum_speed;
+	int err;
+	int i;
+
+	err = of_property_read_string(np, "maximum-speed", &maximum_speed);
+	if (err < 0)
+		return USB_SPEED_UNKNOWN;
+
+	for (i = 0; i < ARRAY_SIZE(speed_names); i++)
+		if (strcmp(maximum_speed, speed_names[i]) == 0)
+			return i;
+
+	return USB_SPEED_UNKNOWN;
+}
+EXPORT_SYMBOL_GPL(of_usb_get_maximum_speed);
+
 #endif
 
 MODULE_LICENSE("GPL");