linux-kernel - Re: [question] NR

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Message-ID: <AANLkTik5N0d9wcaiS538UWQ83E_HhXoWC8nMxVY__1+k@mail.gmail.com>
Date:	Wed, 24 Nov 2010 21:46:06 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [question] NR_IRQS in genirq

On Wed, Nov 24, 2010 at 9:18 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Wed, 24 Nov 2010, Haojian Zhuang wrote:
>
>> Hi all,
>>
>> I'm using the latest kernel 2.6.37-rc1. Now I met some issues on genirq.
>>
>> 1. While SPARSE IRQ is enabled, nr_irqs may be larger than NR_IRQS.
>> But the allocated_irqs bitmap (kernel/irq/irqdesc.c) is restricted in
>> NR_IRQS. Is it an issue?
>
> Why can nr_irqs become larger? Is that a theoretical problem or did
> you run into this ?
>
>

Hi Thomas,

My hardware environment is ARM. Each machine description can specify
nr_irqs. In my implementation of PXA, NR_IRQS is fixed for SoC
internal IRQs. And there's some additional board IRQs, we arrange them
between NR_IRQS and nr_irqs. So nr_irqs will be larger than NR_IRQS if
board IRQs exists.

We use dynamic board IRQs since each machine has different
requirement. And CONFIG_HARDIRQ_SW_RESEND is occasionally, I actually
met issue in resend_irqs because of accessing bitmap memory out of
bound.

Do you mean that we shouldn't use SPARSE IRQ by this way?

Best Regards
Haojian
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