linux-kernel - Serial related oops

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Date:	Tue, 20 Feb 2007 13:29:09 +0000
From:	Frederik Deweerdt <deweerdt@...e.fr>
To:	rmk+lkml@....linux.org.uk
Cc:	jose.goncalves@...v.pt, tie-fei.zang@...escale.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Serial related oops

(Sorry for the resend, I forgot to cc the list)
Hi Russell,

It seems that the following change in drivers/serial/8250.c

+
+	/*
+	 * Do a quick test to see if we receive an
+	 * interrupt when we enable the TX irq.
+	 */
+	serial_outp(up, UART_IER, UART_IER_THRI);
+	lsr = serial_in(up, UART_LSR);
+	iir = serial_in(up, UART_IIR);
+	serial_outp(up, UART_IER, 0);
+
+	if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT) {
+		if (!(up->capabilities & UART_BUG_TXEN)) {
+			up->capabilities |= UART_BUG_TXEN;
+			pr_debug("ttyS%d - enabling bad tx status workarounds\n",
+				 port->line);
+		}
+	} else {
+		up->capabilities &= ~UART_BUG_TXEN;
+	}
+

that was introduced in 2.6.12[1], is causing oopses on some hardware. In
particular Jose Goncalves reported[2] an oops in 2.6.16.38 reproducible
(after a few days of open()/close() on the serial port). He bisected this
to that change -thanks for the long debugging Jose ;)-. and reverting
that part of the 2.6.12 git patch seems to fix the problem.
I was wondering:
- what is the goal of the test?
- could this be CONFIGed ?

Regards,
Frederik

PS: CCing Andrew and Zang Roy-r61911 as they seemed to discuss this in
http://lkml.org/lkml/2006/6/13/21

[1]http://lkml.org/lkml/2005/6/23/266
[2]http://lkml.org/lkml/2007/1/26/157
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