linux-kernel - Re: [PATCH] irq: call also chip->irq_mask from irq

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Date:	Wed, 14 Sep 2011 21:01:33 +0300
From:	Tero Kristo <t-kristo@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"LKML" <linux-kernel@...r.kernel.org>,
	"Peter Zijlstra" <peterz@...radead.org>
Subject: Re: [PATCH] irq: call also chip->irq_mask from irq_disable

On Wed, 2011-09-14 at 18:04 +0200, Thomas Gleixner wrote:
> On Wed, 14 Sep 2011, Tero Kristo wrote:
> 
> > Current implementation of the irq_disable only calls chip->irq_disable.
> > This fails to disable interrupt on some chip implementations, as there
> > are two alternative chip specific functions for this task,
> > chip->irq_disable and chip->irq_mask. Added alternative path for
> > chip->irq_disable also.
> 
> This does not fail to do so. It's done on purpose. We don't want to
> access the interrupt chip when we can avoid it.
> 
> So we just mark the interrupt disabled and keep the line enabled.
> When another interrupt happens, then the handling code checks the
> disabled state of the line, masks the interrupt on the hardware level
> and sets the pending bit. This is documented behaviour and not going
> to change.
> 
> http://docs.blackfin.uclinux.org/kernel/generated/genericirq/ch04s03.html#Delayed_interrupt_disable
> 

Hmm okay, that makes sense.

> What are you trying to solve ?

I was seeing a hang with a chain handler implementation that was caused
by this delayed disable implementation, I am using a generic chip with
irq_mask / irq_unmask. Adding this patch to the kernel fixed the hang in
this case. There might be something wrong in my implementation of the
chain handler itself, I'll take a look at it again and try to figure out
another way to avoid it. I have another idea I can pursue, and based on
some initial testing it actually seems to be working.

-Tero



Texas Instruments Oy, Tekniikantie 12, 02150 Espoo. Y-tunnus: 0115040-6. Kotipaikka: Helsinki
 

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