linux-kernel - RE: [PATCH] genirq: for edge interrupt IRQS

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Message-ID: <27240C0AC20F114CBF8149A2696CBE4A1958B9@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 12 Oct 2012 13:03:39 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with
 irq thread



> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Friday, October 12, 2012 8:46 PM
> To: Liu, Chuansheng
> Cc: linux-kernel@...r.kernel.org
> Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with irq
> thread
> 
> On Fri, 12 Oct 2012, Liu, Chuansheng wrote:
> > > -----Original Message-----
> > > From: Thomas Gleixner [mailto:tglx@...utronix.de]
> > > Sent: Friday, October 12, 2012 8:32 PM
> > > To: Liu, Chuansheng
> > > Cc: linux-kernel@...r.kernel.org
> > > Subject: Re: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support
> with irq
> > > thread
> > >
> > > On Fri, 12 Oct 2012, Chuansheng Liu wrote:
> > > >
> > > > In our system, there is one edge interrupt, and we want it to be
> > > > irq thread with IRQS_ONESHOT, and found in handle_edge_irq(),
> > > > even with IRQS_ONESHOT, the irq is still unmasked without care of
> > > > flag IRQS_ONESHOT.
> > > >
> > > > It causes IRQS_ONESHOT can not work well for edge interrupt, but also
> > > > after the irq thread finished with flag IRQS_ONESHOT, the irq will be
> > > > possible to be unmasked again, it should be messing mask/unmask logic.
> > >
> > > This is just wrong. By masking edge interrupts you will run into
> > > situations where you will lose interrupts.
> > >
> > > Can you please explain, why you want to mask your edge interrupt?
> 
> > When I request_irq with irq thread handler and flag IRQS_ONESHOT, if
> > do not mask the edge interrupt, the primary handler and irq thread
> > maybe run at the same time, and in my real case it causes spin
> > deadlock.
> 
> Then your code is simply wrong and you need to fix it instead of hacking a
> workaround into the core code. Locking is not that hard.
I got means, so I want to use flag IRQS_ONESHOT to avoid the case that two
handlers running at the same time. Is it right direction?
But IRQS_ONESHOT does not work well for edge interrupt.
And pasting the IRQS_ONESHOT description:
* IRQS_ONESHOT			- irq is not unmasked in primary handler

And I need irq handler is because some heavy work is needed, it can avoid local
irq disabling time thru irq handler.

> 
> > You means it is not right with IRQS_ONESHOT for edge interrupt?
> 
> It's wrong. Simnply because you can lose interrupts.
> 
>      interrupt raised
>      	 handle_edge_irq()
> 	    mask_ack_irq()
> 	    handle_event()
> 	        wake irq thread
>      reti
> 
>      irq thread runs
>      	 handle device interrupt()
> 				   <--- device issues edge irq
> 	 unmask_irq()
> 
> This interrupt is not delivered. So your device stops working. Not
> what you want, right?
Device should not stop:) And even in current handle_edge_irq(), it is possible that losting
Interrupt if primary handler need some time and the irq is quick enough. I says the below
code, it just avoid one time lost.

                        desc->istate |= IRQS_PENDING;
                        mask_ack_irq(desc);


> 
> Thanks,
> 
> 	tglx
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