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

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Date:	Tue, 4 Mar 2014 11:34:13 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Stephen Warren <swarren@...dotorg.org>
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 Tue, 4 Mar 2014, 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.
> 
> enum {
>      IRQ_CHIP_TYPES_MASK	= 0x0f,
>      IRQ_CHIP_DEFAULT_MASK	= 0xf0,
>      IRQ_CHIP_EXISTING_FLAGS	....
> }

We need to extend the mask to indicate whether the chip supports
BOTH_EDGES. A chip can support FALLING and RISING, but not both at the
same time. For the set_type side the current BOTH = FALLING | RISING
is fine, but for checking the supported type it's not sufficient.

Thanks,

	tglx


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