Hi,

  USB debug port only supports 8 byte rx/tx packets. Although spec implies that "if a packet larger than eight bytes is received from the remote computer, the device must break the larger packet into eight-byte packets before sending the data to the Debug Port", the real PLX NET20DC device does not handle it right - data is corrupted on debug port end if serial interface sends >8 byte urbs. Patch below fixes the issue by limiting tx urb to 8 byte.

Signed off by: Aleks Gorelov <dared1st@yahoo.com>

--- a/drivers/usb/serial/usb_debug.c    2008-06-19 14:52:19.000000000 -0700
+++ b/drivers/usb/serial/usb_debug.c    2008-06-19 14:48:32.000000000 -0700
@@ -15,6 +15,8 @@
 #include <linux/usb.h>
 #include <linux/usb/serial.h>
 
+#define USB_DEBUG_MAX_PACKET_SIZE    8
+
 static struct usb_device_id id_table [] = {
     { USB_DEVICE(0x0525, 0x127a) },
     { },
@@ -29,6 +31,12 @@
     .no_dynamic_id =     1,
 };
 
+int usb_debug_open (struct usb_serial_port *port, struct file *filp)
+{
+    port->bulk_out_size = USB_DEBUG_MAX_PACKET_SIZE;
+    return usb_serial_generic_open(port, filp);
+}
+
 static struct usb_serial_driver debug_device = {
     .driver = {
         .owner =    THIS_MODULE,
@@ -39,6 +47,7 @@
     .num_bulk_in =        NUM_DONT_CARE,
     .num_bulk_out =        NUM_DONT_CARE,
     .num_ports =        1,
+    .open =            usb_debug_open,
 };
 
 static int __init debug_init(void)

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