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

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Date:	Mon, 9 May 2016 16:44:56 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Marc Zyngier <marc.zyngier@....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 16:10, 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 :-)

>> We could add a WARN to the existing irq_set_irq_type() or may be just a
>> pr_warn() if a WARN is too verbose so people can fix up any issues.
>>
>> I am also wondering if patch 4/17 "iqdomain: Fix handling of type
>> settings for existing mappings" could generate a lot of reports
>> interrupts failing due to bad firmware? I wonder if I should tone this
>> patch down to a warning message as well as opposed to a complete failure.
> 
> We'll see. We can always tone it down a notch, should it prove to be too noisy...
> So far, I haven't seen it firing. On the other hand, I get the following stuff
> on my APM board:
> 
> [    0.000000] GIC: PPI0 is either secure or misconfigured
> [    0.000000] GIC: PPI13 is either secure or misconfigured
> [    0.000000] arm_arch_timer: WARNING: Invalid trigger for IRQ1, assuming level low
> [    0.000000] arm_arch_timer: WARNING: Please fix your firmware
> [    0.000000] arm_arch_timer: WARNING: Invalid trigger for IRQ2, assuming level low
> [    0.000000] arm_arch_timer: WARNING: Please fix your firmware
> 
> Pretty awesome...

Indeed.

Jon