[PATCH v3] serdev: Add serdev_device_write subroutine

[Andrey Smirnov <andrew.smirnov@gmail.com>]

Add serdev_device_write() a blocking call allowing to transfer
arbitraty amount of data (potentially exceeding amount that
serdev_device_write_buf can process in a single call)

To support that, also add serdev_device_write_wakeup().

Drivers wanting to use full extent of serdev_device_write
functionality are expected to provide serdev_device_write_wakeup() as
a sole handler of .write_wakeup event or call it as a part of driver's
custom .write_wakeup code.

Because serdev_device_write() subroutine is a superset of
serdev_device_write_buf() the patch re-impelements latter is terms of
the former. For drivers watning to just use serdev_device_write_buf()
.write_wakeup handler is optional.

Cc: cphealy@gmail.com
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
---

Changes since v2 (see [v2]):

	- Changed subject and commit message wording to better reflect
          nature of the patch

	- Various spelling, formatting, documentation and wording
          fixes as caught/suggested by Andy

Changes since v1 (see [v1]):

	- Make timeout to be a total(as opposed to per-iteration)
          timeout

	- Keep serdev_device_write_buf() as a wrapper arount
          serdev_device_write() for compatibility

[v2] https://lkml.org/lkml/2017/3/28/942
[v1] https://lkml.org/lkml/2017/3/20/650

 drivers/tty/serdev/core.c | 36 +++++++++++++++++++++++++++++++-----
 include/linux/serdev.h    | 17 +++++++++++++++--
 2 files changed, 46 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index f4c6c90..6701d10 100644
--- a/drivers/tty/serdev/core.c
+++ b/drivers/tty/serdev/core.c
@@ -116,17 +116,41 @@ void serdev_device_close(struct serdev_device *serdev)
 }
 EXPORT_SYMBOL_GPL(serdev_device_close);
 
-int serdev_device_write_buf(struct serdev_device *serdev,
-			    const unsigned char *buf, size_t count)
+void serdev_device_write_wakeup(struct serdev_device *serdev)
+{
+	complete(&serdev->write_comp);
+}
+EXPORT_SYMBOL_GPL(serdev_device_write_wakeup);
+
+int serdev_device_write(struct serdev_device *serdev,
+			const unsigned char *buf, size_t count,
+			unsigned long timeout)
 {
 	struct serdev_controller *ctrl = serdev->ctrl;
+	int ret;
 
-	if (!ctrl || !ctrl->ops->write_buf)
+	if (!ctrl || !ctrl->ops->write_buf ||
+	    (timeout && !serdev->ops->write_wakeup))
 		return -EINVAL;
 
-	return ctrl->ops->write_buf(ctrl, buf, count);
+	mutex_lock(&serdev->write_lock);
+	do {
+		reinit_completion(&serdev->write_comp);
+
+		ret = ctrl->ops->write_buf(ctrl, buf, count);
+		if (ret < 0)
+			break;
+
+		buf += ret;
+		count -= ret;
+
+	} while (count &&
+		 (timeout = wait_for_completion_timeout(&serdev->write_comp,
+							timeout)));
+	mutex_unlock(&serdev->write_lock);
+	return ret < 0 ? ret : (count ? -ETIMEDOUT : 0);
 }
-EXPORT_SYMBOL_GPL(serdev_device_write_buf);
+EXPORT_SYMBOL_GPL(serdev_device_write);
 
 void serdev_device_write_flush(struct serdev_device *serdev)
 {
@@ -232,6 +256,8 @@ struct serdev_device *serdev_device_alloc(struct serdev_controller *ctrl)
 	serdev->dev.parent = &ctrl->dev;
 	serdev->dev.bus = &serdev_bus_type;
 	serdev->dev.type = &serdev_device_type;
+	init_completion(&serdev->write_comp);
+	mutex_init(&serdev->write_lock);
 	return serdev;
 }
 EXPORT_SYMBOL_GPL(serdev_device_alloc);
diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index 5176cdc..0beaff8 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -39,12 +39,16 @@ struct serdev_device_ops {
  * @nr:		Device number on serdev bus.
  * @ctrl:	serdev controller managing this device.
  * @ops:	Device operations.
+ * @write_comp	Completion used by serdev_device_write() internally
+ * @write_lock	Lock to serialize access when writing data
  */
 struct serdev_device {
 	struct device dev;
 	int nr;
 	struct serdev_controller *ctrl;
 	const struct serdev_device_ops *ops;
+	struct completion write_comp;
+	struct mutex write_lock;
 };
 
 static inline struct serdev_device *to_serdev_device(struct device *d)
@@ -186,7 +190,8 @@ int serdev_device_open(struct serdev_device *);
 void serdev_device_close(struct serdev_device *);
 unsigned int serdev_device_set_baudrate(struct serdev_device *, unsigned int);
 void serdev_device_set_flow_control(struct serdev_device *, bool);
-int serdev_device_write_buf(struct serdev_device *, const unsigned char *, size_t);
+void serdev_device_write_wakeup(struct serdev_device *);
+int serdev_device_write(struct serdev_device *, const unsigned char *, size_t, unsigned long);
 void serdev_device_write_flush(struct serdev_device *);
 int serdev_device_write_room(struct serdev_device *);
 
@@ -223,7 +228,8 @@ static inline unsigned int serdev_device_set_baudrate(struct serdev_device *sdev
 	return 0;
 }
 static inline void serdev_device_set_flow_control(struct serdev_device *sdev, bool enable) {}
-static inline int serdev_device_write_buf(struct serdev_device *sdev, const unsigned char *buf, size_t count)
+static inline int serdev_device_write(struct serdev_device *sdev, const unsigned char *buf,
+				      size_t count, unsigned long timeout)
 {
 	return -ENODEV;
 }
@@ -259,4 +265,11 @@ static inline struct device *serdev_tty_port_register(struct tty_port *port,
 static inline void serdev_tty_port_unregister(struct tty_port *port) {}
 #endif /* CONFIG_SERIAL_DEV_CTRL_TTYPORT */
 
+static inline int serdev_device_write_buf(struct serdev_device *serdev,
+					  const unsigned char *data,
+					  size_t count)
+{
+	return serdev_device_write(serdev, data, count, 0);
+}
+
 #endif /*_LINUX_SERDEV_H */
-- 
2.9.3