[PATCH] cdc-acm: some enhancement on acm delayed write

[Xiao Jin <jin.xiao@intel.com>]

From: xiao jin <jin.xiao@intel.com>
Date: Tue, 25 Mar 2014 15:54:36 +0800
Subject: [PATCH] cdc-acm: some enhancement on acm delayed write

We find two problems on acm tty write delayed mechanism.
(1) When acm resume, the delayed wb will be started. But now
only one write can be saved during acm suspend. More acm write
may be abandoned.
(2) acm tty port ASYNCB_INITIALIZED flag will be cleared when
close. If acm resume callback run after ASYNCB_INITIALIZED flag
cleared, there will have no chance for delayed write to start.
That lead to acm_wb.use can't be cleared. If user space open
acm tty again and try to setd, tty will be blocked in
tty_wait_until_sent for ever.

This patch have two modification.
(1) use list_head to save the write acm_wb during acm suspend.
It can ensure no acm write abandoned.
(2) enable flush buffer callback when acm tty close. acm delayed
wb will start before acm port shutdown callback, it make sure
the delayed acm_wb.use to be cleared. The patch also clear
acm_wb.use and acm.transmitting when port shutdown.

Signed-off-by: xiao jin <jin.xiao@intel.com>
Reviewed-by: David Cohen <david.a.cohen@linux.intel.com>
---
  drivers/usb/class/cdc-acm.c |   56 
++++++++++++++++++++++++++++++-------------
  drivers/usb/class/cdc-acm.h |    3 ++-
  2 files changed, 42 insertions(+), 17 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 900f7ff..cfe00b2 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -217,6 +217,24 @@ static int acm_start_wb(struct acm *acm, struct 
acm_wb *wb)
  }

  /*
+ * Delayed write.
+ */
+static int acm_start_delayed_wb(struct acm *acm)
+{
+	struct acm_wb *wb, *n_wb;
+	LIST_HEAD(delay_wb_list);
+
+	spin_lock_irq(&acm->write_lock);
+	list_replace_init(&acm->delayed_wb_list, &delay_wb_list);
+	spin_unlock_irq(&acm->write_lock);
+	list_for_each_entry_safe(wb, n_wb,
+			&delay_wb_list, delay) {
+		list_del(&wb->delay);
+		acm_start_wb(acm, wb);
+	}
+}
+
+/*
   * attributes exported through sysfs
   */
  static ssize_t show_caps
@@ -580,8 +598,11 @@ static void acm_port_shutdown(struct tty_port *port)
  		usb_autopm_get_interface(acm->control);
  		acm_set_control(acm, acm->ctrlout = 0);
  		usb_kill_urb(acm->ctrlurb);
-		for (i = 0; i < ACM_NW; i++)
+		acm->transmitting = 0;
+		for (i = 0; i < ACM_NW; i++) {
  			usb_kill_urb(acm->wb[i].urb);
+			acm->wb[i].use = 0;
+		}
  		for (i = 0; i < acm->rx_buflimit; i++)
  			usb_kill_urb(acm->read_urbs[i]);
  		acm->control->needs_remote_wakeup = 0;
@@ -608,6 +629,8 @@ static void acm_tty_close(struct tty_struct *tty, 
struct file *filp)
  {
  	struct acm *acm = tty->driver_data;
  	dev_dbg(&acm->control->dev, "%s\n", __func__);
+	/* Set flow_stopped to enable flush buffer*/
+	tty->flow_stopped = 1;
  	tty_port_close(&acm->port, tty, filp);
  }

@@ -646,10 +669,7 @@ static int acm_tty_write(struct tty_struct *tty,

  	usb_autopm_get_interface_async(acm->control);
  	if (acm->susp_count) {
-		if (!acm->delayed_wb)
-			acm->delayed_wb = wb;
-		else
-			usb_autopm_put_interface_async(acm->control);
+		list_add_tail(&wb->delay, &acm->delayed_wb_list);
  		spin_unlock_irqrestore(&acm->write_lock, flags);
  		return count;	/* A white lie */
  	}
@@ -688,6 +708,18 @@ static int acm_tty_chars_in_buffer(struct 
tty_struct *tty)
  	return (ACM_NW - acm_wb_is_avail(acm)) * acm->writesize;
  }

+static void acm_tty_flush_buffer(struct tty_struct *tty)
+{
+	struct acm *acm = tty->driver_data;
+
+	/* flush delayed write buffer */
+	if (!acm->disconnected) {
+		usb_autopm_get_interface(acm->control);
+		acm_start_delayed_wb(acm);
+		usb_autopm_put_interface(acm->control);
+	}
+}
+
  static void acm_tty_throttle(struct tty_struct *tty)
  {
  	struct acm *acm = tty->driver_data;
@@ -1346,6 +1378,7 @@ made_compressed_probe:
  		snd->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
  		snd->instance = acm;
  	}
+	INIT_LIST_HEAD(&acm->delayed_wb_list);

  	usb_set_intfdata(intf, acm);

@@ -1540,7 +1573,6 @@ static int acm_suspend(struct usb_interface *intf, 
pm_message_t message)
  static int acm_resume(struct usb_interface *intf)
  {
  	struct acm *acm = usb_get_intfdata(intf);
-	struct acm_wb *wb;
  	int rv = 0;
  	int cnt;

@@ -1555,16 +1587,7 @@ static int acm_resume(struct usb_interface *intf)
  	if (test_bit(ASYNCB_INITIALIZED, &acm->port.flags)) {
  		rv = usb_submit_urb(acm->ctrlurb, GFP_NOIO);

-		spin_lock_irq(&acm->write_lock);
-		if (acm->delayed_wb) {
-			wb = acm->delayed_wb;
-			acm->delayed_wb = NULL;
-			spin_unlock_irq(&acm->write_lock);
-			acm_start_wb(acm, wb);
-		} else {
-			spin_unlock_irq(&acm->write_lock);
-		}
-
+		acm_start_delayed_wb(acm);
  		/*
  		 * delayed error checking because we must
  		 * do the write path at all cost
@@ -1823,6 +1846,7 @@ static const struct tty_operations acm_ops = {
  	.throttle =		acm_tty_throttle,
  	.unthrottle =		acm_tty_unthrottle,
  	.chars_in_buffer =	acm_tty_chars_in_buffer,
+	.flush_buffer =		acm_tty_flush_buffer,
  	.break_ctl =		acm_tty_break_ctl,
  	.set_termios =		acm_tty_set_termios,
  	.tiocmget =		acm_tty_tiocmget,
diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
index e38dc78..42d6427 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -69,6 +69,7 @@ struct acm_wb {
  	int use;
  	struct urb		*urb;
  	struct acm		*instance;
+	struct list_head	delay;
  };

  struct acm_rb {
@@ -120,7 +121,7 @@ struct acm {
  	unsigned int throttled:1;			/* actually throttled */
  	unsigned int throttle_req:1;			/* throttle requested */
  	u8 bInterval;
-	struct acm_wb *delayed_wb;			/* write queued for a device about to be 
woken */
+	struct list_head delayed_wb_list;		/* delayed wb list */
  };

  #define CDC_DATA_INTERFACE_TYPE	0x0a
-- 
1.7.9.5