[PATCH 1/5] tty: serdev: Export functions to pause receive_buf callback calls

[Markus Probst <markus.probst@posteo.de>]

These functions will be used to simply the serdev rust abstraction. It
also contributes to the fixing of 2 race conditions in the serdev rust
abstraction.

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 drivers/tty/serdev/core.c           | 50 ++++++++++++++++++++++++++++++++++++-
 drivers/tty/serdev/serdev-ttyport.c | 32 ++++++++++++++++++++++++
 include/linux/serdev.h              |  6 +++++
 3 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index 7500efcdfc21..7d24f16710cb 100644
--- a/drivers/tty/serdev/core.c
+++ b/drivers/tty/serdev/core.c
@@ -187,6 +187,51 @@ void serdev_device_close(struct serdev_device *serdev)
 }
 EXPORT_SYMBOL_GPL(serdev_device_close);
 
+/**
+ * serdev_device_pause_rx() - pause data receive
+ * @serdev:	serdev device
+ *
+ * Pause calls to receive_buf.
+ *
+ * The caller must guarantee that this does not run concurrently with
+ * `serdev_device_open` or `serdev_device_close`.
+ *
+ * Note that if a call to receive_buf is currently executed, the function will
+ * sleep until it has finished.
+ */
+void serdev_device_pause_rx(struct serdev_device *serdev)
+{
+	struct serdev_controller *ctrl = serdev->ctrl;
+
+	if (!ctrl || !ctrl->ops->pause_rx)
+		return;
+
+	ctrl->ops->pause_rx(ctrl);
+}
+EXPORT_SYMBOL_GPL(serdev_device_pause_rx);
+
+/**
+ * serdev_device_resume_rx() - resume data receive
+ * @serdev:	serdev device
+ *
+ * Resume calls to receive_buf.
+ *
+ * The caller must guarantee that this does not run concurrently with
+ * `serdev_device_open` or `serdev_device_close`.
+ *
+ * This can be called even if not paused to ensure data receive is active.
+ */
+void serdev_device_resume_rx(struct serdev_device *serdev)
+{
+	struct serdev_controller *ctrl = serdev->ctrl;
+
+	if (!ctrl || !ctrl->ops->resume_rx)
+		return;
+
+	ctrl->ops->resume_rx(ctrl);
+}
+EXPORT_SYMBOL_GPL(serdev_device_resume_rx);
+
 static void devm_serdev_device_close(void *serdev)
 {
 	serdev_device_close(serdev);
@@ -398,6 +443,7 @@ EXPORT_SYMBOL_GPL(serdev_device_break_ctl);
 static int serdev_drv_probe(struct device *dev)
 {
 	const struct serdev_device_driver *sdrv = to_serdev_device_driver(dev->driver);
+	struct serdev_device *sdev = to_serdev_device(dev);
 	int ret;
 
 	ret = dev_pm_domain_attach(dev, PD_FLAG_ATTACH_POWER_ON |
@@ -405,7 +451,9 @@ static int serdev_drv_probe(struct device *dev)
 	if (ret)
 		return ret;
 
-	return sdrv->probe(to_serdev_device(dev));
+	serdev_device_resume_rx(sdev);
+
+	return sdrv->probe(sdev);
 }
 
 static void serdev_drv_remove(struct device *dev)
diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c
index bab1b143b8a6..85ab454c2f13 100644
--- a/drivers/tty/serdev/serdev-ttyport.c
+++ b/drivers/tty/serdev/serdev-ttyport.c
@@ -6,9 +6,11 @@
 #include <linux/serdev.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
+#include <linux/tty_flip.h>
 #include <linux/poll.h>
 
 #define SERPORT_ACTIVE		1
+#define SERPORT_PAUSE_RX	2
 
 struct serport {
 	struct tty_port *port;
@@ -32,6 +34,9 @@ static size_t ttyport_receive_buf(struct tty_port *port, const u8 *cp,
 	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
 		return 0;
 
+	if (test_bit(SERPORT_PAUSE_RX, &serport->flags))
+		return 0;
+
 	ret = serdev_controller_receive_buf(ctrl, cp, count);
 
 	dev_WARN_ONCE(&ctrl->dev, ret > count,
@@ -156,6 +161,31 @@ static void ttyport_close(struct serdev_controller *ctrl)
 	tty_release_struct(tty, serport->tty_idx);
 }
 
+static void ttyport_pause_rx(struct serdev_controller *ctrl)
+{
+	struct serport *serport = serdev_controller_get_drvdata(ctrl);
+	struct tty_struct *tty = serport->tty;
+
+	if (test_bit(SERPORT_ACTIVE, &serport->flags))
+		tty_buffer_lock_exclusive(tty->port);
+
+	set_bit(SERPORT_PAUSE_RX, &serport->flags);
+
+	if (test_bit(SERPORT_ACTIVE, &serport->flags))
+		tty_buffer_unlock_exclusive(tty->port);
+}
+
+static void ttyport_resume_rx(struct serdev_controller *ctrl)
+{
+	struct serport *serport = serdev_controller_get_drvdata(ctrl);
+	struct tty_struct *tty = serport->tty;
+
+	clear_bit(SERPORT_PAUSE_RX, &serport->flags);
+
+	if (test_bit(SERPORT_ACTIVE, &serport->flags))
+		tty_flip_buffer_push(tty->port);
+}
+
 static unsigned int ttyport_set_baudrate(struct serdev_controller *ctrl, unsigned int speed)
 {
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
@@ -260,6 +290,8 @@ static const struct serdev_controller_ops ctrl_ops = {
 	.get_tiocm = ttyport_get_tiocm,
 	.set_tiocm = ttyport_set_tiocm,
 	.break_ctl = ttyport_break_ctl,
+	.pause_rx = ttyport_pause_rx,
+	.resume_rx = ttyport_resume_rx,
 };
 
 struct device *serdev_tty_port_register(struct tty_port *port,
diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index b6c3d957ec15..5cf05df17ddf 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -89,6 +89,8 @@ struct serdev_controller_ops {
 	int (*get_tiocm)(struct serdev_controller *);
 	int (*set_tiocm)(struct serdev_controller *, unsigned int, unsigned int);
 	int (*break_ctl)(struct serdev_controller *ctrl, unsigned int break_state);
+	void (*pause_rx)(struct serdev_controller *ctrl);
+	void (*resume_rx)(struct serdev_controller *ctrl);
 };
 
 /**
@@ -194,6 +196,8 @@ static inline size_t serdev_controller_receive_buf(struct serdev_controller *ctr
 int serdev_device_open(struct serdev_device *);
 void serdev_device_close(struct serdev_device *);
 int devm_serdev_device_open(struct device *, struct serdev_device *);
+void serdev_device_pause_rx(struct serdev_device *serdev);
+void serdev_device_resume_rx(struct serdev_device *serdev);
 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 u8 *, size_t);
@@ -233,6 +237,8 @@ static inline int serdev_device_open(struct serdev_device *sdev)
 	return -ENODEV;
 }
 static inline void serdev_device_close(struct serdev_device *sdev) {}
+static inline void serdev_device_pause_rx(struct serdev_device *serdev) {}
+static inline void serdev_device_resume_rx(struct serdev_device *serdev) {}
 static inline unsigned int serdev_device_set_baudrate(struct serdev_device *sdev, unsigned int baudrate)
 {
 	return 0;

-- 
2.55.0