2 files changed, 25 insertions, 11 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 98199628e394..023cf5d45a9d 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/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:
diff --git a/include/linux/usb/cdc.h b/include/linux/usb/cdc.h
index ba617c372455..956edf3bbecb 100644
--- a/include/linux/usb/cdc.h
+++ b/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;