[PATCH v1 2/3] drivers/tty: convert tty_port to use kthread_worker

[Oleksij Rempel <o.rempel@pengutronix.de>]

From: Steven Walter <stevenrwalter@gmail.com>

Use kthread_worker instead of workqueues.  For now there is only a
single workqueue, but the intention is to bring back the "low_latency"
tty option, along with a second high-priority kthread worker.

Even without a second worker this patch allows to give a higher priority
to tty processing by modifying the priority of the corresponding
kthread.

Signed-off-by: Steven Walter <stevenrwalter@gmail.com>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/tty/tty_buffer.c | 21 ++++++++++++++-------
 drivers/tty/tty_io.c     |  1 +
 include/linux/tty.h      |  7 ++++---
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index e0090e65d83a..18bd7f48a319 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/types.h>
+#include <linux/kthread.h>
 #include <linux/errno.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
@@ -497,7 +498,7 @@ receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
  *		 'consumer'
  */
 
-static void flush_to_ldisc(struct work_struct *work)
+static void flush_to_ldisc(struct kthread_work *work)
 {
 	struct tty_port *port = container_of(work, struct tty_port, buf.work);
 	struct tty_bufhead *buf = &port->buf;
@@ -557,10 +558,16 @@ void tty_flip_buffer_push(struct tty_port *port)
 }
 EXPORT_SYMBOL(tty_flip_buffer_push);
 
+static DEFINE_KTHREAD_WORKER(tty_buffer_worker);
+
 bool tty_buffer_queue_work(struct tty_port *port)
 {
-	struct tty_bufhead *buf = &port->buf;
-	return schedule_work(&buf->work);
+	return kthread_queue_work(&tty_buffer_worker, &port->buf.work);
+}
+
+void tty_buffer_init_kthread(void)
+{
+	kthread_run(kthread_worker_fn, &tty_buffer_worker, "tty");
 }
 
 /**
@@ -582,7 +589,7 @@ void tty_buffer_init(struct tty_port *port)
 	init_llist_head(&buf->free);
 	atomic_set(&buf->mem_used, 0);
 	atomic_set(&buf->priority, 0);
-	INIT_WORK(&buf->work, flush_to_ldisc);
+	kthread_init_work(&buf->work, flush_to_ldisc);
 	buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
 }
 
@@ -614,12 +621,12 @@ bool tty_buffer_restart_work(struct tty_port *port)
 	return tty_buffer_queue_work(port);
 }
 
-bool tty_buffer_cancel_work(struct tty_port *port)
+void tty_buffer_cancel_work(struct tty_port *port)
 {
-	return cancel_work_sync(&port->buf.work);
+	tty_buffer_flush_work(port);
 }
 
 void tty_buffer_flush_work(struct tty_port *port)
 {
-	flush_work(&port->buf.work);
+	kthread_flush_work(&port->buf.work);
 }
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index bfe9ad85b362..5fd7cecbe4e7 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3476,6 +3476,7 @@ void console_sysfs_notify(void)
  */
 int __init tty_init(void)
 {
+	tty_buffer_init_kthread();
 	cdev_init(&tty_cdev, &tty_fops);
 	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
 	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 226a9eff0766..924c1093967e 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -3,9 +3,9 @@
 #define _LINUX_TTY_H
 
 #include <linux/fs.h>
+#include <linux/kthread.h>
 #include <linux/major.h>
 #include <linux/termios.h>
-#include <linux/workqueue.h>
 #include <linux/tty_driver.h>
 #include <linux/tty_ldisc.h>
 #include <linux/mutex.h>
@@ -84,7 +84,7 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
 
 struct tty_bufhead {
 	struct tty_buffer *head;	/* Queue head */
-	struct work_struct work;
+	struct kthread_work work;
 	struct mutex	   lock;
 	atomic_t	   priority;
 	struct tty_buffer sentinel;
@@ -510,8 +510,9 @@ extern void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld);
 extern bool tty_buffer_queue_work(struct tty_port *port);
 extern void tty_buffer_init(struct tty_port *port);
 extern void tty_buffer_set_lock_subclass(struct tty_port *port);
+extern void tty_buffer_init_kthread(void);
 extern bool tty_buffer_restart_work(struct tty_port *port);
-extern bool tty_buffer_cancel_work(struct tty_port *port);
+extern void tty_buffer_cancel_work(struct tty_port *port);
 extern void tty_buffer_flush_work(struct tty_port *port);
 extern speed_t tty_termios_baud_rate(struct ktermios *termios);
 extern speed_t tty_termios_input_baud_rate(struct ktermios *termios);
-- 
2.19.1