Merge branch 'pm-cpuidle'

[firefly-linux-kernel-4.4.55.git] / drivers / tty / tty_buffer.c

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index fb042b9a8d6881c06bd2812a4808dd6c73f43aac..c043136fbe5198cf0a7a8704254fc28763ecd0b9 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -28,6 +28,52 @@
  */
 #define TTYB_MEM_LIMIT 65536
 
+/*
+ * We default to dicing tty buffer allocations to this many characters
+ * in order to avoid multiple page allocations. We know the size of
+ * tty_buffer itself but it must also be taken into account that the
+ * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
+ * logic this must match
+ */
+
+#define TTY_BUFFER_PAGE        (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
+
+
+/**
+ *     tty_buffer_lock_exclusive       -       gain exclusive access to buffer
+ *     tty_buffer_unlock_exclusive     -       release exclusive access
+ *
+ *     @port - tty_port owning the flip buffer
+ *
+ *     Guarantees safe use of the line discipline's receive_buf() method by
+ *     excluding the buffer work and any pending flush from using the flip
+ *     buffer. Data can continue to be added concurrently to the flip buffer
+ *     from the driver side.
+ *
+ *     On release, the buffer work is restarted if there is data in the
+ *     flip buffer
+ */
+
+void tty_buffer_lock_exclusive(struct tty_port *port)
+{
+       struct tty_bufhead *buf = &port->buf;
+
+       atomic_inc(&buf->priority);
+       mutex_lock(&buf->lock);
+}
+
+void tty_buffer_unlock_exclusive(struct tty_port *port)
+{
+       struct tty_bufhead *buf = &port->buf;
+       int restart;
+
+       restart = buf->head->commit != buf->head->read;
+
+       atomic_dec(&buf->priority);
+       mutex_unlock(&buf->lock);
+       if (restart)
+               queue_work(system_unbound_wq, &buf->work);
+}
 
 /**
  *     tty_buffer_space_avail  -       return unused buffer space
@@ -150,28 +196,6 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
                llist_add(&b->free, &buf->free);
 }
 
-/**
- *     __tty_buffer_flush              -       flush full tty buffers
- *     @tty: tty to flush
- *
- *     flush all the buffers containing receive data. Caller must
- *     hold the buffer lock and must have ensured no parallel flush to
- *     ldisc is running.
- */
-
-static void __tty_buffer_flush(struct tty_port *port)
-{
-       struct tty_bufhead *buf = &port->buf;
-       struct tty_buffer *next;
-
-       while ((next = buf->head->next) != NULL) {
-               tty_buffer_free(port, buf->head);
-               buf->head = next;
-       }
-       WARN_ON(buf->head != buf->tail);
-       buf->head->read = buf->head->commit;
-}
-
 /**
  *     tty_buffer_flush                -       flush full tty buffers
  *     @tty: tty to flush
@@ -180,7 +204,7 @@ static void __tty_buffer_flush(struct tty_port *port)
  *     being processed by flush_to_ldisc then we defer the processing
  *     to that function
  *
- *     Locking: takes flush_mutex to ensure single-threaded flip buffer
+ *     Locking: takes buffer lock to ensure single-threaded flip buffer
  *              'consumer'
  */
 
@@ -188,13 +212,18 @@ void tty_buffer_flush(struct tty_struct *tty)
 {
        struct tty_port *port = tty->port;
        struct tty_bufhead *buf = &port->buf;
+       struct tty_buffer *next;
 
-       buf->flushpending = 1;
+       atomic_inc(&buf->priority);
 
-       mutex_lock(&buf->flush_mutex);
-       __tty_buffer_flush(port);
-       buf->flushpending = 0;
-       mutex_unlock(&buf->flush_mutex);
+       mutex_lock(&buf->lock);
+       while ((next = buf->head->next) != NULL) {
+               tty_buffer_free(port, buf->head);
+               buf->head = next;
+       }
+       buf->head->read = buf->head->commit;
+       atomic_dec(&buf->priority);
+       mutex_unlock(&buf->lock);
 }
 
 /**
@@ -400,7 +429,7 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
  *
  *     The receive_buf method is single threaded for each tty instance.
  *
- *     Locking: takes flush_mutex to ensure single-threaded flip buffer
+ *     Locking: takes buffer lock to ensure single-threaded flip buffer
  *              'consumer'
  */
 
@@ -419,14 +448,14 @@ static void flush_to_ldisc(struct work_struct *work)
        if (disc == NULL)
                return;
 
-       mutex_lock(&buf->flush_mutex);
+       mutex_lock(&buf->lock);
 
        while (1) {
                struct tty_buffer *head = buf->head;
                int count;
 
-               /* Ldisc or user is trying to flush the buffers. */
-               if (buf->flushpending)
+               /* Ldisc or user is trying to gain exclusive access */
+               if (atomic_read(&buf->priority))
                        break;
 
                count = head->commit - head->read;
@@ -443,7 +472,7 @@ static void flush_to_ldisc(struct work_struct *work)
                        break;
        }
 
-       mutex_unlock(&buf->flush_mutex);
+       mutex_unlock(&buf->lock);
 
        tty_ldisc_deref(disc);
 }
@@ -499,13 +528,12 @@ void tty_buffer_init(struct tty_port *port)
 {
        struct tty_bufhead *buf = &port->buf;
 
-       mutex_init(&buf->flush_mutex);
+       mutex_init(&buf->lock);
        tty_buffer_reset(&buf->sentinel, 0);
        buf->head = &buf->sentinel;
        buf->tail = &buf->sentinel;
        init_llist_head(&buf->free);
        atomic_set(&buf->memory_used, 0);
-       buf->flushpending = 0;
+       atomic_set(&buf->priority, 0);
        INIT_WORK(&buf->work, flush_to_ldisc);
 }
-