tty: uartclk value from serial_core exposed to sysfs

Added file /sys/devices/.../tty/ttySX/uartclk to allow reading
uartclk value in struct uart_port in serial_core via sysfs.

tty_register_device() has been generalized and refactored in order
to add support for setting drvdata and attribute_group to the device.
Signed-off-by: Tomas Hlavacek <tmshlvck@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-tty

@@ -17,3 +17,12 @@ Description:
 		 device, like 'tty1'.
 		 The file supports poll() to detect virtual
 		 console switches.
+
+What:		/sys/class/tty/ttyS0/uartclk
+Date:		Sep 2012
+Contact:	Tomas Hlavacek <tmshlvck@gmail.com>
+Description:
+		 Shows the current uartclk value associated with the
+		 UART port in serial_core, that is bound to TTY like ttyS0.
+		 uartclk = 16 * baud_base
+

drivers/tty/serial/serial_core.c

@@ -2309,6 +2309,36 @@ struct tty_driver *uart_console_device(struct console *co, int *index)
 	return p->tty_driver;
 }
 
+static ssize_t uart_get_attr_uartclk(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	int ret;
+
+	struct tty_port *port = dev_get_drvdata(dev);
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	mutex_lock(&state->port.mutex);
+	ret = snprintf(buf, PAGE_SIZE, "%d\n", state->uart_port->uartclk);
+	mutex_unlock(&state->port.mutex);
+
+	return ret;
+}
+
+static DEVICE_ATTR(uartclk, S_IRUSR | S_IRGRP, uart_get_attr_uartclk, NULL);
+
+static struct attribute *tty_dev_attrs[] = {
+	&dev_attr_uartclk.attr,
+	NULL,
+	};
+
+static struct attribute_group tty_dev_attr_group = {
+	.attrs = tty_dev_attrs,
+	};
+
+static const struct attribute_group *tty_dev_attr_groups[] = {
+	&tty_dev_attr_group,
+	NULL
+	};
+
 /**
  *	uart_add_one_port - attach a driver-defined port structure
  *	@drv: pointer to the uart low level driver structure for this port
@@ -2362,8 +2392,8 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this ports parameters.
 	 */
-	tty_dev = tty_port_register_device(port, drv->tty_driver, uport->line,
-			uport->dev);
+	tty_dev = tty_register_device_attr(drv->tty_driver, uport->line,
+			uport->dev, port, tty_dev_attr_groups);
 	if (likely(!IS_ERR(tty_dev))) {
 		device_set_wakeup_capable(tty_dev, 1);
 	} else {

drivers/tty/tty_io.c

@@ -3041,9 +3041,39 @@ static int tty_cdev_add(struct tty_driver *driver, dev_t dev,
 struct device *tty_register_device(struct tty_driver *driver, unsigned index,
 				   struct device *device)
 {
-	struct device *ret;
+	return tty_register_device_attr(driver, index, device, NULL, NULL);
+}
+EXPORT_SYMBOL(tty_register_device);
+
+/**
+ *	tty_register_device_attr - register a tty device
+ *	@driver: the tty driver that describes the tty device
+ *	@index: the index in the tty driver for this tty device
+ *	@device: a struct device that is associated with this tty device.
+ *		This field is optional, if there is no known struct device
+ *		for this tty device it can be set to NULL safely.
+ *	@drvdata: Driver data to be set to device.
+ *	@attr_grp: Attribute group to be set on device.
+ *
+ *	Returns a pointer to the struct device for this tty device
+ *	(or ERR_PTR(-EFOO) on error).
+ *
+ *	This call is required to be made to register an individual tty device
+ *	if the tty driver's flags have the TTY_DRIVER_DYNAMIC_DEV bit set.  If
+ *	that bit is not set, this function should not be called by a tty
+ *	driver.
+ *
+ *	Locking: ??
+ */
+struct device *tty_register_device_attr(struct tty_driver *driver,
+				   unsigned index, struct device *device,
+				   void *drvdata,
+				   const struct attribute_group **attr_grp)
+{
 	char name[64];
-	dev_t dev = MKDEV(driver->major, driver->minor_start) + index;
+	dev_t devt = MKDEV(driver->major, driver->minor_start) + index;
+	struct device *dev = NULL;
+	int retval = -ENODEV;
 	bool cdev = false;
 
 	if (index >= driver->num) {
@@ -3058,19 +3088,38 @@ struct device *tty_register_device(struct tty_driver *driver, unsigned index,
 		tty_line_name(driver, index, name);
 
 	if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
-		int error = tty_cdev_add(driver, dev, index, 1);
-		if (error)
-			return ERR_PTR(error);
+		retval = tty_cdev_add(driver, devt, index, 1);
+		if (retval)
+			goto error;
 		cdev = true;
 	}
 
-	ret = device_create(tty_class, device, dev, NULL, name);
-	if (IS_ERR(ret) && cdev)
-		cdev_del(&driver->cdevs[index]);
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev) {
+		retval = -ENOMEM;
+		goto error;
+	}
 
-	return ret;
+	dev->devt = devt;
+	dev->class = tty_class;
+	dev->parent = device;
+	dev_set_name(dev, "%s", name);
+	dev->groups = attr_grp;
+	dev_set_drvdata(dev, drvdata);
+
+	retval = device_register(dev);
+	if (retval)
+		goto error;
+
+	return dev;
+
+error:
+	put_device(dev);
+	if (cdev)
+		cdev_del(&driver->cdevs[index]);
+	return ERR_PTR(retval);
 }
-EXPORT_SYMBOL(tty_register_device);
+EXPORT_SYMBOL_GPL(tty_register_device_attr);
 
 /**
  * 	tty_unregister_device - unregister a tty device

include/linux/tty.h

@@ -412,6 +412,10 @@ extern int tty_register_driver(struct tty_driver *driver);
 extern int tty_unregister_driver(struct tty_driver *driver);
 extern struct device *tty_register_device(struct tty_driver *driver,
 					  unsigned index, struct device *dev);
+extern struct device *tty_register_device_attr(struct tty_driver *driver,
+				unsigned index, struct device *device,
+				void *drvdata,
+				const struct attribute_group **attr_grp);
 extern void tty_unregister_device(struct tty_driver *driver, unsigned index);
 extern int tty_read_raw_data(struct tty_struct *tty, unsigned char *bufp,
 			     int buflen);