linux-kernel - Re: [PATCH V3 06/17] irqdomain: Don't set type when mapping an IRQ

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Message-ID: <5731D223.2080503@arm.com>
Date:	Tue, 10 May 2016 13:20:51 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Jon Hunter <jonathanh@...dia.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>
Cc:	Kevin Hilman <khilman@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-tegra@...r.kernel.org, linux-omap@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 06/17] irqdomain: Don't set type when mapping an IRQ

On 09/05/16 16:44, Jon Hunter wrote:
> 
> On 09/05/16 16:10, Marc Zyngier wrote:
>> On 09/05/16 14:13, Jon Hunter wrote:
>>> On 09/05/16 13:23, Marc Zyngier wrote:
> 
> [snip]
> 
>>>> This patch have the effect of making misconfigured PPIs absolutely
>>>> obvious. I still need to wrap my head around the root cause, but here's
>>>> the findings I have so far:
>>>>
>>>> - kvmtool generates a DT with the wrong trigger information (edge
>>>> instead of level) for the timer.
>>>> - with this patch applied, "cyclictest -S" reliably locks up when run in
>>>> a guest (missing a timer interrupt, goodbye CPU).
>>>> - Either fixing kvmtool or reverting that patch makes it work reliably
>>>> again.
>>>>
>>>> My gut feeling is that until that patch, the failing irq_set_irq_type()
>>>> wasn't affecting the kernel's view of the trigger (it was still treated
>>>> as level). With this patch, the kernel now trusts whatever is coming
>>>> from the firmware, and the misconfiguration becomes obvious. And just
>>>> grepping through the DT files for arm and arm64 sends makes me thing
>>>> "Holly effin' crap!".
>>>>
>>>> I'm not saying that we shouldn't perform this change though. But it is
>>>> quite obvious that it is going to break an awful lot of existing code
>>>> and platforms. I'm also cooking a small patch for the arch timer (which
>>>> seems to be described in DT with a fairly high level of brokenness), so
>>>> that we can mop-up most of the brain damage.
>>>
>>> Hmmm ... yes I see. I wonder if we should make the setting of the type
>>> here dependent upon PM being enabled for an irqchip? We could check to
>>> see if the .parent_device is populated and if so only then save the type
>>> and otherwise just set it as we do today.
>>
>> I don't really like the idea of having multiple code paths for the same thing.
>> This is very error prone, and likely to bitrot pretty quickly.
> 
> True. However, we really need this change for irqchips and runtime-pm.
> So to confirm what are you suggesting we do? We could add a WARN around
> irq_set_irq_type() in irq_create_fwspec_mapping() for v4.7 and see how
> many complaints we get :-)

Let's add a pr_warn(), and see how noisy this becomes. We may have to
remove it if it becomes too loud though.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...