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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Josh Cartwright <joshc@ni.com>
Cc: Sean Nyekj?r <sean.nyekjaer@prevas.dk>,
	linux-serial@vger.kernel.org, linux-rt-users@vger.kernel.org,
	Jon Ringle <jringle@gridpoint.com>,
	Jakub Kicinski <kubakici@wp.pl>
Subject: Re: sc16is7xx: a lot of time is spend in sc16is7xx_port_irq
Date: Fri, 26 Feb 2016 12:43:40 +0100	[thread overview]
Message-ID: <20160226114340.GC8318@linutronix.de> (raw)
In-Reply-To: <20160224223547.GF9598@jcartwri.amer.corp.natinst.com>

* Josh Cartwright | 2016-02-24 16:35:47 [-0600]:

>On Wed, Feb 24, 2016 at 06:39:46PM +0100, Sean Nyekj?r wrote:
>> CC'ing RT
>
>I'm assuming this is with the other patch killing off IRQF_ONESHOT?
>
>> On 2016-02-24 16:31, Sean Nyekjær wrote:
>> >Hi
>> >
>> >I'm using the sc16is750 on an imx6d platform with RT patches applied.
>> >
>> >I have observed that sometimes the driver locks the whole system as is
>> >loops inside the sc16is7xx_port_irq.
>> >I have applied some debug and seen we are looping upto 130000 times in the
>> >while(1) loop.
>> >The SC16IS7XX_IIR_REG does signal the SC16IS7XX_IIR_XOFFI_SRC but the
>> >SC16IS7XX_IER_XOFFI_BIT is not set.
>
>Ouch.
>
>I don't quite understand how the interrupt handling in this driver is
>supposed to work.  sc16is7xx_irq() is invoked to handle the interrupt,
>but it does absolutely nothing to squelch it...  how does this not cause
>an interrupt storm?  The irq core is free to unmask the interrupt when
>the handler return IRQ_HANDLED, and if you're dealing with
>level-sensitive interrupts...

The irqcore does not shut down the driver because it always returns
IRQ_HANDLED. The reason why don't end up in a storm is the IRQF_ONESHOT
part. However it should use proper irq threads and not this homegrow
stuff. I could be a bug in general and not related to -RT.

>  Josh

Sebastian
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  reply	other threads:[~2016-02-26 11:43 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <56CDCCE6.5020801@prevas.dk>
2016-02-24 17:39 ` sc16is7xx: a lot of time is spend in sc16is7xx_port_irq Sean Nyekjær
2016-02-24 17:39   ` Sean Nyekjær
2016-02-24 22:35   ` Josh Cartwright
2016-02-26 11:43     ` Sebastian Andrzej Siewior [this message]
2016-02-26 11:48       ` [PATCH] tty: serial: sc16is7xx: use threaded interrupts instead of homegrow Sebastian Andrzej Siewior
2016-02-26 14:34         ` Kuba Kicinski
2016-02-26 16:52           ` Josh Cartwright
2016-02-26 18:26             ` Kuba Kicinski
2016-02-26 19:00               ` Josh Cartwright
2016-03-07 16:41                 ` Sebastian Andrzej Siewior
2016-03-07 16:58                   ` Josh Cartwright
2016-03-07 17:22                     ` Sean Nyekjær
2016-03-08 21:18                     ` Jakub Kicinski
2016-03-09  7:03                       ` Sean Nyekjær
2016-03-09  7:03                         ` Sean Nyekjær
2016-03-09 11:13                         ` Jakub Kicinski
2016-03-09 11:13                           ` Jakub Kicinski
2016-03-09 12:04                           ` Sebastian Andrzej Siewior

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