usb: gadget: allocate & giveback serial ports instead hard code them

This patch removes gserial_setup() and gserial_cleanup() and adds
gserial_alloc_line() and gserial_free_line() to replace them.

The initial setup of u_serial happens now on module load time. A
maximum of four TTY ports can be requested which is the current limit.
In theory we could extend this limit, the hard limit is the number of
available endpoints.
alloc_tty_driver() is now called at module init time with the max
available ports. The per-line footprint here is on 32bit is 3 * size of
pointer + 60 bytes (for cdevs).
The remaining memory (struct gs_port) is allocated once a port is
requested.

With this change it is possible to load g_multi and g_serial at the same
time. GS0 receives the module that is loaded first, GS1 is received by
the next module and so on. With the configfs interface the port number
can be exported and the device node is more predictable. Nothing changes
for g_serial and friends as long as one module is used.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/serial.c

@@ -127,6 +127,7 @@ module_param(n_ports, uint, 0);
 MODULE_PARM_DESC(n_ports, "number of ports to create, default=1");
 
 /*-------------------------------------------------------------------------*/
+static unsigned char tty_lines[MAX_U_SERIAL_PORTS];
 
 static int __init serial_bind_acm_config(struct usb_configuration *c)
 {
@@ -134,7 +135,7 @@ static int __init serial_bind_acm_config(struct usb_configuration *c)
 	int status = 0;
 
 	for (i = 0; i < n_ports && status == 0; i++)
-		status = acm_bind_config(c, i);
+		status = acm_bind_config(c, tty_lines[i]);
 	return status;
 }
 
@@ -144,7 +145,7 @@ static int __init serial_bind_obex_config(struct usb_configuration *c)
 	int status = 0;
 
 	for (i = 0; i < n_ports && status == 0; i++)
-		status = obex_bind_config(c, i);
+		status = obex_bind_config(c, tty_lines[i]);
 	return status;
 }
 
@@ -154,7 +155,7 @@ static int __init serial_bind_gser_config(struct usb_configuration *c)
 	int status = 0;
 
 	for (i = 0; i < n_ports && status == 0; i++)
-		status = gser_bind_config(c, i);
+		status = gser_bind_config(c, tty_lines[i]);
 	return status;
 }
 
@@ -165,13 +166,25 @@ static struct usb_configuration serial_config_driver = {
 	.bmAttributes	= USB_CONFIG_ATT_SELFPOWER,
 };
 
+static int gs_unbind(struct usb_composite_dev *cdev)
+{
+	int i;
+
+	for (i = 0; i < n_ports; i++)
+		gserial_free_line(tty_lines[i]);
+	return 0;
+}
+
 static int __init gs_bind(struct usb_composite_dev *cdev)
 {
 	int			status;
+	int			cur_line;
 
-	status = gserial_setup(cdev->gadget, n_ports);
-	if (status < 0)
-		return status;
+	for (cur_line = 0; cur_line < n_ports; cur_line++) {
+		status = gserial_alloc_line(&tty_lines[cur_line]);
+		if (status)
+			goto fail;
+	}
 
 	/* Allocate string descriptor numbers ... note that string
 	 * contents can be overridden by the composite_dev glue.
@@ -209,7 +222,9 @@ static int __init gs_bind(struct usb_composite_dev *cdev)
 	return 0;
 
 fail:
-	gserial_cleanup();
+	cur_line--;
+	while (cur_line >= 0)
+		gserial_free_line(tty_lines[cur_line--]);
 	return status;
 }
 
@@ -219,6 +234,7 @@ static __refdata struct usb_composite_driver gserial_driver = {
 	.strings	= dev_strings,
 	.max_speed	= USB_SPEED_SUPER,
 	.bind		= gs_bind,
+	.unbind		= gs_unbind,
 };
 
 static int __init init(void)
@@ -254,6 +270,5 @@ module_init(init);
 static void __exit cleanup(void)
 {
 	usb_composite_unregister(&gserial_driver);
-	gserial_cleanup();
 }
 module_exit(cleanup);