On Sunday 06 December 2009 19:10:48 Benjamin Herrenschmidt wrote:
> On Sun, 2009-12-06 at 01:01 -0600, Rob Landley wrote:
> > Trying again with a few likely-looking cc's from the MAINTAINERS file:
> >
> > Summary:
> >
> > The PMACZILOG serial driver last worked in 2.6.28. It was broken by
> > commit f751928e0ddf54ea4fe5546f35e99efc5b5d9938 by Alan Cox making bits
> > of the tty layer dynamically allocated. The PMACZILOG driver wasn't
> > properly converted, it works with interrupts disabled (for boot
> > messages), but as soon as interrupts are enabled (PID 1 spawns) the next
> > write to the serial console panics the kernel.
>
> Ah looks like I missed that... I'll dig. Thanks for the report.
>
> Cheers,
> Ben.
Ok, here's the fix. It's not the _right_ fix, but it Works For Me (tm) and I'll
leave it to you guys to figure out what this _means_:
Signed-off-by: Rob Landley <r...@landley.net>
diff -ru build/packages/linux/drivers/serial/serial_core.c
build/packages/linux2/drivers/serial/serial_core.c
--- build/packages/linux/drivers/serial/serial_core.c 2009-12-02
21:51:21.000000000 -0600
+++ build/packages/linux2/drivers/serial/serial_core.c 2009-12-08
06:17:06.000000000 -0600
@@ -113,7 +113,7 @@
static void uart_tasklet_action(unsigned long data)
{
struct uart_state *state = (struct uart_state *)data;
- tty_wakeup(state->port.tty);
+ if (state->port.tty) tty_wakeup(state->port.tty);
}
static inline void
That one line workaround makes the panic go away, and things seem to work fine
from there.
I note that pmac_zilog.c function pmz_receiv_chars() has the following chunk:
/* Sanity check, make sure the old bug is no longer happening */
if (uap->port.state == NULL || uap->port.state->port.tty == NULL) {
WARN_ON(1);
(void)read_zsdata(uap);
return NULL;
}
Which doesn't catch this because it's the write code path (not the read code
path) that's running into
this.
Rob
--
Latency is more important than throughput. It's that simple. - Linus Torvalds
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