linux-kernel - Re: [PATCH V3 1/5] genirq: define flag IRQ_SRC_DST

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Message-ID: <5315F7DB.6000700@wwwdotorg.org>
Date:	Tue, 04 Mar 2014 08:57:15 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	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>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-tegra@...r.kernel.org, Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH V3 1/5] genirq: define flag IRQ_SRC_DST_INVERTED, and
 accessors

On 03/04/2014 03:04 AM, Thomas Gleixner wrote:
> On Mon, 3 Mar 2014, Stephen Warren wrote:
> 
>> From: Stephen Warren <swarren@...dia.com>
>>
>> Some devices have configurable IRQ output polarities. Software might
>> use IRQ_TYPE_* to determine how to configure such a device's IRQ
>> output polarity in order to match how the IRQ controller input is
>> configured. If the board or SoC inverts the signal between the
>> device's IRQ output and controller's IRQ output, software must be
>> aware of this fact, in order to program the IRQ output to the correct
>> (i.e. opposite) polarity. This flag provides that information.
> 
> So what you're saying is:
> 
> Device IRQ output --> [Optional Inverter Logic] --> IRQ controller input.
> 
> And you're storing the information about the presence of the inverter
> logic in the irq itself, but the core does not make any use of it and
> you let the device driver deal with the outcome.
> 
> This sucks as all affected drivers have to implement the same sanity
> logic for this.
> 
> Why don't you implement a core function which tells the driver which
> polarity to select? That requires a few more changes, but I think it's
> worth it for other reasons.
> 
> Right now the set_type logic requires the irq chip drivers to
> implement sanity checking and default selections for TYPE_NONE. We can
> be more clever about that and add this information to the irq chip
> flags.

I don't see any such checking in drivers/irqchip/irq-gic.c; it rejects
any type other than IRQ_TYPE_LEVEL_HIGH or IRQ_TYPE_EDGE_RISING, and I
don't see any mention of TYPE_NONE in that file. Is the driver incomplete?

Instead of adding all this extra logic to the core, what do you think of
simply telling each driver that has a configurable interrupt output
polarity exactly which polarity to use. This information would come from
device tree or platform data. This is what I implemented in V1/V2 of
this series:

http://www.spinics.net/lists/devicetree/msg23648.html

Is that any better, or do you definitely want the IRQ core to manage this?
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