[PATCH] pps: Make pps_gen_parport depend on BROKEN

[PATCH] pps: Make pps_gen_parport depend on BROKEN

[Thomas Gleixner]

This driver causes hard lockups, when the active clock soure is
jiffies. The reason is that it loops with interrupts disabled waiting
for a timestamp to be reached by polling getnstimeofday(). Though with
a jiffies clocksource, when that code runs on the same CPU which is
responsible for updating jiffies, then we loop in circles for ever
simply because the timer interrupt cannot update jiffies. So both UP
and SMP can be affected.

There is no easy fix for that problem so make it depend on BROKEN for
now.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Cc: Rodolfo Giometti <giometti@linux.it>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>
---
 drivers/pps/generators/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/drivers/pps/generators/Kconfig
===================================================================
--- linux-2.6.orig/drivers/pps/generators/Kconfig
+++ linux-2.6/drivers/pps/generators/Kconfig
@@ -6,7 +6,7 @@ comment "PPS generators support"
 
 config PPS_GENERATOR_PARPORT
 	tristate "Parallel port PPS signal generator"
-	depends on PARPORT
+	depends on PARPORT && BROKEN
 	help
 	  If you say yes here you get support for a PPS signal generator which
 	  utilizes STROBE pin of a parallel port to send PPS signals. It uses

Re: [PATCH] pps: Make pps_gen_parport depend on BROKEN

[john stultz]

On Fri, 2011-02-18 at 22:16 +0100, Thomas Gleixner wrote:
> This driver causes hard lockups, when the active clock soure is
> jiffies. The reason is that it loops with interrupts disabled waiting
> for a timestamp to be reached by polling getnstimeofday(). Though with
> a jiffies clocksource, when that code runs on the same CPU which is
> responsible for updating jiffies, then we loop in circles for ever
> simply because the timer interrupt cannot update jiffies. So both UP
> and SMP can be affected.

Yuck.

Alexander, Rodolfo: Instead of polling on gtod, could you take a
timestamp, calculate the delay and then use udelay()?

thanks
-john

Re: [PATCH] pps: Make pps_gen_parport depend on BROKEN

[Alexander Gordeev]

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Hi John,

В Fri, 18 Feb 2011 13:34:41 -0800
john stultz <johnstul@us.ibm.com> пишет:

> On Fri, 2011-02-18 at 22:16 +0100, Thomas Gleixner wrote:
> > This driver causes hard lockups, when the active clock soure is
> > jiffies. The reason is that it loops with interrupts disabled waiting
> > for a timestamp to be reached by polling getnstimeofday(). Though with
> > a jiffies clocksource, when that code runs on the same CPU which is
> > responsible for updating jiffies, then we loop in circles for ever
> > simply because the timer interrupt cannot update jiffies. So both UP
> > and SMP can be affected.
> 
> Yuck.
> 
> Alexander, Rodolfo: Instead of polling on gtod, could you take a
> timestamp, calculate the delay and then use udelay()?

Sure, it's possible but it would be less precise IMHO. I'll test it.

-- 
  Alexander

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