linux-kernel - Re: [PATCH v2 2/2] irqchip: al-fic: Introduce Amazon's Annapurna Labs Fabric Interrupt Controller Driver

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Message-ID: <54df139cc6cfef9202be6b945c968c3040591607.camel@kernel.crashing.org>
Date:   Thu, 06 Jun 2019 08:06:05 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Marc Zyngier <marc.zyngier@....com>,
        "Shenhar, Talel" <talel@...zon.com>, nicolas.ferre@...rochip.com,
        jason@...edaemon.net, mark.rutland@....com,
        mchehab+samsung@...nel.org, robh+dt@...nel.org,
        davem@...emloft.net, shawn.lin@...k-chips.com, tglx@...utronix.de,
        devicetree@...r.kernel.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org
Cc:     dwmw@...zon.co.uk, jonnyc@...zon.com, hhhawa@...zon.com,
        ronenk@...zon.com, hanochu@...zon.com, barakw@...zon.com
Subject: Re: [PATCH v2 2/2] irqchip: al-fic: Introduce Amazon's Annapurna
 Labs Fabric Interrupt Controller Driver

On Wed, 2019-06-05 at 16:12 +0100, Marc Zyngier wrote:
> > Those error messages are control path messages. if we return the same 
> > error value from here and from the previous error, how can we 
> > differentiate between the two error cases by looking at the log?
> > 
> > Having informative printouts seems like a good idea for bad 
> > configuration cases as such, wouldn't you agree?
> 
> I completely disagree. The kernel log isn't a dumping ground for this
> kind of pretty useless information. Furthermore, the irq subsystem will
> also shout at you when it gets an error, so no need to add insult to injury.
> 
> If you really want to keep them around, turn them into pr_debug.

I disagree Marc. This is a rather bad error which indicates that the device-tree
is probably incorrect (or the HW was wired in a way that cannot work).

Basically a given FIC can either be entirely level sensitive or entirely edge
sensitive. This catches cases where the DT has routed a mixed of both to the
same FIC. Definitely worth barfing loudly about rather than trying to understand
subtle odd misbehaviours of the device in the field.

Cheers,
Ben.