[PATCH 1/1] [RFC] uartclk from serial_core exposed to sysfs

[Tomas Hlavacek <tmshlvck@gmail.com>]

Support for read/modify of uartclk via sysfs added.
It may prove useful with some no-name cards that
has different oscillator speeds and no distinguishing
PCI IDs to allow autodetection. It allows better integration
with udev and/or init scripts.

Signed-off-by: Tomas Hlavacek <tmshlvck@gmail.com>
---
 drivers/tty/serial/serial_core.c |   54 ++++++++++++++++++++++++++++++++++++++
 drivers/tty/tty_io.c             |   17 ++++++++++++
 include/linux/tty.h              |    2 ++
 3 files changed, 73 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a21dc8e..059b438 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2293,6 +2293,46 @@ struct tty_driver *uart_console_device(struct console *co, int *index)
 	return p->tty_driver;
 }
 
+static ssize_t get_attr_uartclk(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	int ret;
+
+	struct uart_state *state = (struct uart_state *)(dev_get_drvdata(dev));
+	mutex_lock(&state->port.mutex);
+	ret = snprintf(buf, PAGE_SIZE, "%d\n", state->uart_port->uartclk);
+	mutex_unlock(&state->port.mutex);
+	return ret;
+}
+
+static ssize_t set_attr_uartclk(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct uart_state *state = (struct uart_state *)(dev_get_drvdata(dev));
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	mutex_lock(&state->port.mutex);
+
+	/*
+	 * Check value: baud_base has to be more than 9600
+	 * and uartclock = baud_base * 16 .
+	 */
+	if (val >= 153600)
+		state->uart_port->uartclk = val;
+
+	mutex_unlock(&state->port.mutex);
+
+	return count;
+}
+
+static DEVICE_ATTR(uartclk, S_IRUGO | S_IWUSR, get_attr_uartclk,
+		set_attr_uartclk);
+
 /**
  *	uart_add_one_port - attach a driver-defined port structure
  *	@drv: pointer to the uart low level driver structure for this port
@@ -2355,6 +2395,14 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 	}
 
 	/*
+	 * Expose uartclk in sysfs. Use driverdata of the tty device for
+	 * referencing the UART port.
+	 */
+	dev_set_drvdata(tty_dev, state);
+	if (device_create_file(tty_dev, &dev_attr_uartclk) < 0)
+		dev_err(tty_dev, "Failed to add uartclk attr\n");
+
+	/*
 	 * Ensure UPF_DEAD is not set.
 	 */
 	uport->flags &= ~UPF_DEAD;
@@ -2397,6 +2445,12 @@ int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 	mutex_unlock(&port->mutex);
 
 	/*
+	 * Remove uartclk file from sysfs.
+	 */
+	device_remove_file(tty_lookup_device(drv->tty_driver, uport->line),
+			&dev_attr_uartclk);
+
+	/*
 	 * Remove the devices from the tty layer
 	 */
 	tty_unregister_device(drv->tty_driver, uport->line);
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index b425c79..8ea8622 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3049,6 +3049,23 @@ void tty_unregister_device(struct tty_driver *driver, unsigned index)
 }
 EXPORT_SYMBOL(tty_unregister_device);
 
+/*
+ *	tty_lookup_device - lookup a tty device
+ *	@driver: the tty driver that describes the tty device
+ *	@index: the index in the tty driver for this tty device
+ *
+ *	This function returns a struct device pointer when device has
+ *	been found and NULL otherwise.
+ *
+ *	Locking: ??
+ */
+struct device *tty_lookup_device(struct tty_driver *driver, unsigned index)
+{
+	dev_t devt = MKDEV(driver->major, driver->minor_start) + index;
+	return class_find_device(tty_class, NULL, &devt, dev_match_devt);
+}
+EXPORT_SYMBOL(tty_lookup_device);
+
 struct tty_driver *__alloc_tty_driver(int lines, struct module *owner)
 {
 	struct tty_driver *driver;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 9f47ab5..5d408a1 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -410,6 +410,8 @@ 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_lookup_device(struct tty_driver *driver,
+					unsigned index);
 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);
-- 
1.7.10.4