Patchwork pmac_zilog: Workaround problem due to interrupt on closed port

login
register
mail settings
Submitter Benjamin Herrenschmidt
Date Jan. 11, 2010, 3:51 a.m.
Message ID <1263181902.724.94.camel@pasglop>
Download mbox | patch
Permalink /patch/42586/
State Accepted, archived
Commit 02ab851324dc7e2fc75787f7fae71187092be7ed
Delegated to: Benjamin Herrenschmidt
Headers show

Comments

Benjamin Herrenschmidt - Jan. 11, 2010, 3:51 a.m.
It seems that in qemu, we can see an interrupt in R3 despite the
fact that it's masked in W1. The chip doesn't actually issue an
interrupt, but we can "see" it when taking an interrupt for the
other channel. This may be a qemu bug ... or not, so let's be
safe and avoid calling into the UART layer when that happens which
woulc cause a crash.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

David: This would affect sunzilog as well I believe. I'm not sure
if it's a bug in qemu emulation of the ESCC or if a real ESCC can
show it so I decided to be safe :-) The ESCC doc I have doesn't
appear to specify whether the interrupt status bits in R3 are
prior or post masking by W1. I can reproduce that by having the
kernel low level "udbg" debug console on channel B and the main
console on channel A (which is itself an uncommon setup).
Rob Landley - Jan. 11, 2010, 8:28 a.m.
On Sunday 10 January 2010 21:51:42 Benjamin Herrenschmidt wrote:
> It seems that in qemu, we can see an interrupt in R3 despite the
> fact that it's masked in W1. The chip doesn't actually issue an
> interrupt, but we can "see" it when taking an interrupt for the
> other channel. This may be a qemu bug ... or not, so let's be
> safe and avoid calling into the UART layer when that happens which
> woulc cause a crash.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Acked-by: Rob Landley <rob@landley.net>

Tested it, and it worked for me.

Thanks,

Rob

Patch

diff --git a/drivers/serial/pmac_zilog.c b/drivers/serial/pmac_zilog.c
index 0700cd1..683e66f 100644
--- a/drivers/serial/pmac_zilog.c
+++ b/drivers/serial/pmac_zilog.c
@@ -411,6 +411,17 @@  static void pmz_transmit_chars(struct uart_pmac_port *uap)
 		goto ack_tx_int;
 	}
 
+	/* Under some circumstances, we see interrupts reported for
+	 * a closed channel. The interrupt mask in R1 is clear, but
+	 * R3 still signals the interrupts and we see them when taking
+	 * an interrupt for the other channel (this could be a qemu
+	 * bug but since the ESCC doc doesn't specify precsiely whether
+	 * R3 interrup status bits are masked by R1 interrupt enable
+	 * bits, better safe than sorry). --BenH.
+	 */
+	if (!ZS_IS_OPEN(uap))
+		goto ack_tx_int;
+
 	if (uap->port.x_char) {
 		uap->flags |= PMACZILOG_FLAG_TX_ACTIVE;
 		write_zsdata(uap, uap->port.x_char);