[Xen-changelog] [xen-unstable] Revert part of 23811:f1349a968a5a "ns16550: Simplify UART..."

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir@xxxxxxx>
# Date 1318435888 -3600
# Node ID dcb2bd283dcaa9a72859cf6b454ad4a8a2129bf2
# Parent  48aa733d0767cf24f6c346c3fc0e573bccf4aa47
Revert part of 23811:f1349a968a5a "ns16550: Simplify UART..."

The change to poll LSR.THRE in a loop from __ns16550_poll is a bug.
We can loop indefinitely if there are no chars to transmit.

Thanks to Jan for spotting it.

Signed-off-by: Keir Fraser <keir@xxxxxxx>
---


diff -r 48aa733d0767 -r dcb2bd283dca xen/drivers/char/ns16550.c
--- a/xen/drivers/char/ns16550.c        Wed Oct 12 16:21:32 2011 +0100
+++ b/xen/drivers/char/ns16550.c        Wed Oct 12 17:11:28 2011 +0100
@@ -157,18 +157,15 @@
 {
     struct serial_port *port = this_cpu(poll_port);
     struct ns16550 *uart = port->uart;
-    char lsr;
 
     if ( uart->intr_works )
         return; /* Interrupts work - no more polling */
 
-    while ( (lsr = ns_read_reg(uart, LSR)) & (LSR_DR|LSR_THRE) )
-    {
-        if ( lsr & LSR_THRE )
-            serial_tx_interrupt(port, regs);
-        if ( lsr & LSR_DR )
-            serial_rx_interrupt(port, regs);
-    }
+    while ( ns_read_reg(uart, LSR) & LSR_DR )
+        serial_rx_interrupt(port, regs);
+
+    if ( ns_read_reg(uart, LSR) & LSR_THRE )
+        serial_tx_interrupt(port, regs);
 
     set_timer(&uart->timer, NOW() + MILLISECS(uart->timeout_ms));
 }

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