usb: gadget: configfs: Add max_speed setting

Some functions support speeds other than SuperSpeed. Add max_speed
attribute to configfs gadget allowing user to specify the maximum speed
the composite driver supports. The valid input speed names are
super-speed-plus, super-speed, high-speed, full-speed, and low-speed.
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/configfs-usb-gadget

@@ -16,6 +16,10 @@ Description:
 				write UDC's name found in /sys/class/udc/*
 				to bind a gadget, empty string "" to unbind.
 
+		max_speed	- maximum speed the driver supports. Valid
+				names are super-speed-plus, super-speed,
+				high-speed, full-speed, and low-speed.
+
 		bDeviceClass	- USB device class code
 		bDeviceSubClass	- USB device subclass code
 		bDeviceProtocol	- USB device protocol code

drivers/usb/gadget/configfs.c

@@ -293,6 +293,47 @@ static ssize_t gadget_dev_desc_UDC_store(struct config_item *item,
 	return ret;
 }
 
+static ssize_t gadget_dev_desc_max_speed_show(struct config_item *item,
+					      char *page)
+{
+	enum usb_device_speed speed = to_gadget_info(item)->composite.max_speed;
+
+	return sprintf(page, "%s\n", usb_speed_string(speed));
+}
+
+static ssize_t gadget_dev_desc_max_speed_store(struct config_item *item,
+					       const char *page, size_t len)
+{
+	struct gadget_info *gi = to_gadget_info(item);
+
+	mutex_lock(&gi->lock);
+
+	/* Prevent changing of max_speed after the driver is binded */
+	if (gi->composite.gadget_driver.udc_name)
+		goto err;
+
+	if (strncmp(page, "super-speed-plus", 16) == 0)
+		gi->composite.max_speed = USB_SPEED_SUPER_PLUS;
+	else if (strncmp(page, "super-speed", 11) == 0)
+		gi->composite.max_speed = USB_SPEED_SUPER;
+	else if (strncmp(page, "high-speed", 10) == 0)
+		gi->composite.max_speed = USB_SPEED_HIGH;
+	else if (strncmp(page, "full-speed", 10) == 0)
+		gi->composite.max_speed = USB_SPEED_FULL;
+	else if (strncmp(page, "low-speed", 9) == 0)
+		gi->composite.max_speed = USB_SPEED_LOW;
+	else
+		goto err;
+
+	gi->composite.gadget_driver.max_speed = gi->composite.max_speed;
+
+	mutex_unlock(&gi->lock);
+	return len;
+err:
+	mutex_unlock(&gi->lock);
+	return -EINVAL;
+}
+
 CONFIGFS_ATTR(gadget_dev_desc_, bDeviceClass);
 CONFIGFS_ATTR(gadget_dev_desc_, bDeviceSubClass);
 CONFIGFS_ATTR(gadget_dev_desc_, bDeviceProtocol);
@@ -302,6 +343,7 @@ CONFIGFS_ATTR(gadget_dev_desc_, idProduct);
 CONFIGFS_ATTR(gadget_dev_desc_, bcdDevice);
 CONFIGFS_ATTR(gadget_dev_desc_, bcdUSB);
 CONFIGFS_ATTR(gadget_dev_desc_, UDC);
+CONFIGFS_ATTR(gadget_dev_desc_, max_speed);
 
 static struct configfs_attribute *gadget_root_attrs[] = {
 	&gadget_dev_desc_attr_bDeviceClass,
@@ -313,6 +355,7 @@ static struct configfs_attribute *gadget_root_attrs[] = {
 	&gadget_dev_desc_attr_bcdDevice,
 	&gadget_dev_desc_attr_bcdUSB,
 	&gadget_dev_desc_attr_UDC,
+	&gadget_dev_desc_attr_max_speed,
 	NULL,
 };