linux-kernel - Re: PATCH: 2.6.26-rc8: Fix IRQF_DISABLED for shared interrupts

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Date:	Mon, 30 Jun 2008 08:22:23 +0300
From:	Stefan Becker <Stefan.Becker@...ia.com>
To:	ext David Brownell <david-b@...bell.net>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
CC:	ext Alan Stern <stern@...land.harvard.edu>
Subject: Re: PATCH: 2.6.26-rc8: Fix IRQF_DISABLED for shared interrupts

Hi David,

ext David Brownell wrote:
> 
> By the way, did you notice the oddness of IRQF_SAMPLE_RANDOM there?
> For a shared IRQ, I would rather think that if any IRQ was flagged
> as "too predictable for use as IRQ randomness" (by not having that
> flag set) then the IRQ should never be sampled ... there's some odd
> thought (or non-thought) involved in IRQ sharing.

Good question. What happens when you mix a random and a not-so-random 
source: does the result have an as good random quality as the original 
random source? If the answer is yes then the current code is OK.


> One technical comment:
> 
>> --- a/kernel/irq/internals.h
 >>
>> + * IRQF_DISABLED_CUMULATIVE - one handler in the chain has IRQF_DISABLED
>> set + */
>> +#define IRQF_DISABLED_CUMULATIVE       0x80000000
> 
> I don't think you should need that flag; and if you did, it should be
> declared in <linux/irq.h> to prevent anyone else from using that bit
> for some other purpose.

My fear was that if it is a public flag in linux/interrupt.h then 
somebody might misuse it.


> Instead, I think you can set IRQF_DISABLED in irq_desc[irq].status
> to achieve the same effect.

I actually had the same idea but missed the "irq" in the 
handle_IRQ_event() signature :-(


I'll try to send an updated patch today...

Regards,

	Stefan

---
Stefan Becker
E-Mail: Stefan.Becker@...ia.com
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