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Subject: RE: [BUG][2.6.8.1] serial driver hangs SMP kernel, but not the UP kernel
Date: Thu, 6 Jan 2005 16:47:46 -0600
Message-ID: <4B0A1C17AA88F94289B0704CFABEF1AB0B4D32@ausx2kmps304.aus.amer.dell.com>
Thread-Topic: [BUG][2.6.8.1] serial driver hangs SMP kernel, but not the UP kernel
Thread-Index: AcTAIAVAVRscS9MSR36xZTS1/gcpSAADEUdwDPQ/CKAAEI5dwA==
From: <Tim_T_Murphy@Dell.com>
To: <rmk+lkml@arm.linux.org.uk>
Cc: <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1112
Lines: 33


> anything i can do to avoid dropping characters without using 
> low_latency, which still hangs SMP kernels?

this patch fixes the problem for me, but its probably an awful hack -- a
brief interrupt storm occurs until tty processes its buffer, but IMHO
that's better than dropping characters.

is there a better alternative?
thanks,
tim

--- 8250-orig.c	2005-01-06 16:25:24.000000000 -0600
+++ 8250.c	2005-01-06 16:27:21.000000000 -0600
@@ -989,8 +989,10 @@
 		if (unlikely(tty->flip.count >= TTY_FLIPBUF_SIZE)) {
 			if(tty->low_latency)
 				tty_flip_buffer_push(tty);
-			/* If this failed then we will throw away the
-			   bytes but must do so to clear interrupts */
+			else
+				break;
+			/* If this failed then we will just leave now 
+			   rather than dropping bytes (interrupts not
cleared) */
 		}
 		ch = serial_inp(up, UART_RX);
 		flag = TTY_NORMAL;
-
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