tty: Sort out the USB sysrq changes that wrecked performance

We can't go around calling all sorts of magic per character functions at
full rate 3G data speed.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 4 deletions

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 932d6241b787..3d8dc5671bea 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -424,10 +424,17 @@ static void flush_and_resubmit_read_urb(struct usb_serial_port *port)
         if (!tty)
                 goto done;
 
-        /* Push data to tty */
-        for (i = 0; i < urb->actual_length; i++, ch++) {
-                if (!usb_serial_handle_sysrq_char(port, *ch))
-                        tty_insert_flip_char(tty, *ch, TTY_NORMAL);
+        /* The per character mucking around with sysrq path it too slow for
+           stuff like 3G modems, so shortcircuit it in the 99.9999999% of cases
+           where the USB serial is not a console anyway */
+        if (!port->console || !port->sysrq)
+                tty_insert_flip_string(tty, ch, urb->actual_length);
+        else {
+                /* Push data to tty */
+                for (i = 0; i < urb->actual_length; i++, ch++) {
+                        if (!usb_serial_handle_sysrq_char(port, *ch))
+                                tty_insert_flip_char(tty, *ch, TTY_NORMAL);
+                }
         }
         tty_flip_buffer_push(tty);
         tty_kref_put(tty);