[PATCH] to drivers/parport/ieee1284_ops.c to fix timing dependend

Tim Josling
2003-03-19T08:06:09Z

[PATCH] to drivers/parport/ieee1284_ops.c to fix timing dependent printer
hang
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Philip (Blundell),

I have an HP1100 printer and since I upgraded to a faster CPU the
printer has started hanging. The problem persisteed across 2.0 2.2 and
2.4 kernel versions. I am running Red Hat Linux 8.0 on a Compaq Armada E500.

The problem occurs intermittently. The symptom is that the 'buffer
contains data' light stays on on the printer, but data transfer stops.

I traced the problem to drivers/parport/ieee1284_ops.c function
parport_ieee1284_write_compat. The problem occurs when the parallel port
is not using interrupts. If the printer takes a while to respond the
routine parport_wait_event gets called, if count == 0. However this
routine generally waits almost no time.

Anyway, if 32 repeats of this occur e.g. for a complex document where
the printer is slow, 'wait' ends up as a negative number from repeated
doublings due to the way twos complement arithmetic works in C. In this
case the routine never returns. So no more data gets sent to the printer.

Originally I fixed the problem by adding code to ensure that 'wait'
never got set to anything above 10 seconds (10 * HZ). However the patch
I have sent you does something different, it just ensures that
parport_wait_event never gets called for printer without interrupt. I
have tested this on documents which reproduce the problem

Clearly I am not an expert on the parport code, so my patch may be
incorrect. I have traces using extra printks I put in the code, showing
the wait variable being doubled to negative value, available on request.

Definitely my patch does fix a real problem on my system.

As far as I can tell from browsing the patches since 2.4.18, there has
not been any other fix for this problem to date.

I would appreciate if any replues could be cc'd to me, though I will
look at the archives to see any responses.

Regards,
Tim Josling

--- ChangeLog.original 2003-03-16 09:18:07.000000000 +1100
+++ ChangeLog 2003-03-16 09:20:35.000000000 +1100
@@ -1,3 +1,9 @@
+2003-03-16 Tim Josling <tej@melbpc.org.au>
+
+ * ieee1284_ops.c (parport_ieee1284_write_compat): Avoid calling
+ parport_wait_event if interrupts are not enabled for device, avoid
+ output hang.
+
2002-04-25 Tim Waugh <twaugh@redhat.com>

* parport_serial.c, parport_pc.c: Move some SIIG cards around.

--- ieee1284_ops.c.original 2003-03-16 08:27:33.000000000 +1100
+++ ieee1284_ops.c 2003-03-16 09:17:23.000000000 +1100
@@ -93,7 +93,7 @@
first time around the loop, don't let go of
the port. This way, we find out if we have
our interrupt handler called. */
- if (count && no_irq) {
+ if (count || no_irq) {
parport_release (dev);
__set_current_state (TASK_INTERRUPTIBLE);
schedule_timeout (wait);