linux-kernel - Re: [PATCH 04/15] irqchip/gic: WARN if setting the interrupt type fails

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Date:	Tue, 12 Apr 2016 11:14:52 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Benoît Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>,
	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>,
	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 04/15] irqchip/gic: WARN if setting the interrupt type
 fails

On 12/04/16 09:50, Jon Hunter wrote:
> 
> On 11/04/16 16:39, Marc Zyngier wrote:
>> On 11/04/16 16:31, Jon Hunter wrote:
>>> On 09/04/16 11:58, Marc Zyngier wrote:
> 
> [snip]
> 
>>>> I think we need to phase things. Let's start with warning people for a
>>>> few kernel releases. Actively maintained platforms will quickly address
>>>> the issue (fixing their DT). As I see it, this issue seems rather
>>>> widespread (even kvmtool outputs a DT with the wrong triggering
>>>> information).
>>>>
>>>> Once we've fixed the bulk of the platforms and virtual environments, we
>>>> can start thinking about making it fail harder.
>>>
>>> Ok, so are you OK with this patch as-is? If so, can I add your ACK?
>>
>> It depends where you plan to handle the error. Ideally, I'd keep on
>> returning the error (because that's the right thing to do), and move the
>> WARN_ON() into the core code. We'd keep on ignoring the error as we're
>> doing today, but we'd scream about it.
>>
>> After a couple of releases, we'd turn the WARN_ON into a hard fail.
>>
>> Thoughts?
> 
> I agree that would be best/ideal, but looking at it, I don't believe it
> is possible and this is why I have not done that so far.
> 
> If we were to add the WARN to the core code, then we would need to add a
> warning everywhere __irq_set_trigger() is called. One of the places it
> is called today is from __setup_irq() and today this does the right
> thing and handle any error returned. The problem is that in
> irq_create_fwspec_mapping() we have never checked the return code from
> irq_set_irq_type() (which calls __irq_set_trigger()) or attempted to
> handle any errors. So the problem is that depending on the path through
> which the type is programmed, errors may or may not be detected. This is
> the actual headache :-(
> 
> Given that this problem so far only pertains to GIC PPI interrupts and
> that it is a not a catastrophic error (interrupts still work fine), I
> was thinking we add the warning to the GIC driver.
> 
> May be a less severe change would be to only return an error if
> configuring an SPI fails and if it is a PPI then simply WARN and
> carry-on as we assume we cannot change it.

I'd take that. Limiting it to PPIs would be a minimal change, and the
warning would hopefully make people realize their DT is wrong. Failing
to program an SPI is really not expected, and should definitely explode.

Thanks,

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