From: Keir Fraser <keir.fraser@citrix.com>
Date: Wed, 23 Apr 2008 13:17:35 +0000 (+0100)
Subject: Drop characters if an asynchronous serial tx buffer fills up.
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~14215^2~133
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=989cfc3a3ab54cc5841cf18004f82451933dfb21;p=xen.git

Drop characters if an asynchronous serial tx buffer fills up.
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
---

diff --git a/xen/drivers/char/serial.c b/xen/drivers/char/serial.c
index cf2df9b3df..34c188c641 100644
--- a/xen/drivers/char/serial.c
+++ b/xen/drivers/char/serial.c
@@ -15,6 +15,9 @@
 #include <xen/mm.h>
 #include <xen/serial.h>
 
+/* Never drop characters, even if the async transmit buffer fills. */
+/* #define SERIAL_NEVER_DROP_CHARS 1 */
+
 unsigned int serial_txbufsz = 16384;
 static void __init parse_serial_tx_buffer(const char *s)
 {
@@ -91,22 +94,24 @@ void serial_tx_interrupt(struct serial_port *port, struct cpu_user_regs *regs)
 
 static void __serial_putc(struct serial_port *port, char c)
 {
-    int i;
-
     if ( (port->txbuf != NULL) && !port->sync )
     {
         /* Interrupt-driven (asynchronous) transmitter. */
+#ifdef SERIAL_NEVER_DROP_CHARS
         if ( (port->txbufp - port->txbufc) == serial_txbufsz )
         {
-            /* Buffer is full: we spin, but could alternatively drop chars. */
+            /* Buffer is full: we spin waiting for space to appear. */
+            int i;
             while ( !port->driver->tx_empty(port) )
                 cpu_relax();
             for ( i = 0; i < port->tx_fifo_size; i++ )
                 port->driver->putc(
                     port, port->txbuf[mask_serial_txbuf_idx(port->txbufc++)]);
             port->txbuf[mask_serial_txbuf_idx(port->txbufp++)] = c;
+            return;
         }
-        else if ( ((port->txbufp - port->txbufc) == 0) &&
+#endif
+        if ( ((port->txbufp - port->txbufc) == 0) &&
                   port->driver->tx_empty(port) )
         {
             /* Buffer and UART FIFO are both empty. */