linux-kernel - Re: [PATCH] genirq: fix trigger flags check for shared irqs

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Message-ID: <20160128095955.GA12884@e106950-lin.cambridge.arm.com>
Date:	Thu, 28 Jan 2016 09:59:56 +0000
From:	Brian Starkey <brian.starkey@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, marc.zyngier@....com
Subject: Re: [PATCH] genirq: fix trigger flags check for shared irqs

Hi Thomas,

Thanks for taking a look at this.

On Tue, Jan 26, 2016 at 09:45:32PM +0100, Thomas Gleixner wrote:
>On Tue, 26 Jan 2016, Brian Starkey wrote:
>
>> For shared interrupts, if one requester passes in any IRQF_TRIGGER_*
>> flags whilst another doesn't, __setup_irq() can erroneously fail.
>>
>> The no-flags case should be treated as "already configured", so change
>> __setup_irq() to only check that the flags match if any have been
>> provided.
>
>What happens if that "already configured", i.e. the default setting, is
>conflicting with the newly requested interrupt?
>
>I rather prefer the failure than the resulting silent wreckage.
>

Yes, I agree that would be best avoided. It seems to me that this case
is actually handled a bit lower down:

	} else if (new->flags & IRQF_TRIGGER_MASK) {
		unsigned int nmsk = new->flags & IRQF_TRIGGER_MASK;
		unsigned int omsk = irq_settings_get_trigger_mask(desc);

		if (nmsk != omsk)
			/* hope the handler works with current  trigger mode */
			pr_warning("irq %d uses trigger mode %u; requested %u\n",
				   irq, nmsk, omsk);
	}

Perhaps that should be louder/fatal?

Best regards,

-Brian

>Thanks,
>
>	tglx
>