USB: cdc-acm: fix incorrect throtteling, make set_control optional

this is Joris' fixes reshuffelled and features renamed as David requested.

- acm_set_control is not mandatory, honour that
- throtteling is reset upon open
- throtteling is read consistently when processing input data

Signed-off-by: Joris van Rantwijk <jorispubl@xs4all.nl>
Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/cdc-acm.c

@@ -326,10 +326,16 @@ static void acm_rx_tasklet(unsigned long _acm)
 	struct tty_struct *tty = acm->tty;
 	struct acm_ru *rcv;
 	unsigned long flags;
-	int i = 0;
+	unsigned char throttled;
 	dbg("Entering acm_rx_tasklet");
 
-	if (!ACM_READY(acm) || acm->throttle)
+	if (!ACM_READY(acm))
+		return;
+
+	spin_lock(&acm->throttle_lock);
+	throttled = acm->throttle;
+	spin_unlock(&acm->throttle_lock);
+	if (throttled)
 		return;
 
 next_buffer:
@@ -346,22 +352,20 @@ next_buffer:
 	dbg("acm_rx_tasklet: procesing buf 0x%p, size = %d", buf, buf->size);
 
 	tty_buffer_request_room(tty, buf->size);
-	if (!acm->throttle)
+	spin_lock(&acm->throttle_lock);
+	throttled = acm->throttle;
+	spin_unlock(&acm->throttle_lock);
+	if (!throttled)
 		tty_insert_flip_string(tty, buf->base, buf->size);
 	tty_flip_buffer_push(tty);
 
-	spin_lock(&acm->throttle_lock);
-	if (acm->throttle) {
-		dbg("Throtteling noticed");
-		memmove(buf->base, buf->base + i, buf->size - i);
-		buf->size -= i;
-		spin_unlock(&acm->throttle_lock);
+	if (throttled) {
+		dbg("Throttling noticed");
 		spin_lock_irqsave(&acm->read_lock, flags);
 		list_add(&buf->list, &acm->filled_read_bufs);
 		spin_unlock_irqrestore(&acm->read_lock, flags);
 		return;
 	}
-	spin_unlock(&acm->throttle_lock);
 
 	spin_lock_irqsave(&acm->read_lock, flags);
 	list_add(&buf->list, &acm->spare_read_bufs);
@@ -467,7 +471,8 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
 		goto bail_out;
 	}
 
-	if (0 > acm_set_control(acm, acm->ctrlout = ACM_CTRL_DTR | ACM_CTRL_RTS))
+	if (0 > acm_set_control(acm, acm->ctrlout = ACM_CTRL_DTR | ACM_CTRL_RTS) &&
+	    (acm->ctrl_caps & USB_CDC_CAP_LINE))
 		goto full_bailout;
 
 	INIT_LIST_HEAD(&acm->spare_read_urbs);
@@ -480,6 +485,8 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
 		list_add(&(acm->rb[i].list), &acm->spare_read_bufs);
 	}
 
+	acm->throttle = 0;
+
 	tasklet_schedule(&acm->urb_task);
 
 done:

include/linux/usb/cdc.h

@@ -73,6 +73,13 @@ struct usb_cdc_acm_descriptor {
 	__u8	bmCapabilities;
 } __attribute__ ((packed));
 
+/* capabilities from 5.2.3.3 */
+
+#define USB_CDC_COMM_FEATURE	0x01
+#define USB_CDC_CAP_LINE	0x02
+#define USB_CDC_CAP_BRK	0x04
+#define USB_CDC_CAP_NOTIFY	0x08
+
 /* "Union Functional Descriptor" from CDC spec 5.2.3.8 */
 struct usb_cdc_union_desc {
 	__u8	bLength;