linux-kernel - Re: [PATCH V3 3/3] mfd: stmpe: Update DT support in stmpe driver

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Message-ID: <20121126111845.GG12782@gmail.com>
Date:	Mon, 26 Nov 2012 11:18:45 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Grant Likely <grant.likely@...retlab.ca>, sameo@...ux.intel.com,
	devicetree-discuss@...ts.ozlabs.org, spear-devel@...t.st.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 3/3] mfd: stmpe: Update DT support in stmpe driver

On Fri, 23 Nov 2012, Viresh Kumar wrote:

> On 23 November 2012 15:11, Grant Likely <grant.likely@...retlab.ca> wrote:
> > On Fri, 23 Nov 2012 00:26:20 +0530, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> 
> >> + - irq-trigger                       : IRQ trigger to use for the interrupt to the host
> >> + - irq-invert-polarity               : bool, IRQ line is connected with reversed polarity
> >
> > This looks odd. Normally the interrupt polarity should be encoded in the irq
> > specifier flags field.
> 
> Hi Grant and Lee Jones,
> 
> This looks odd because stmpe is odd, i am taking the discussion held
> with Lee jones to this thread.

STMPE isn't odd or special in any way. :)

> So, how interrupt stuff works currently in DT..
> We have a interrupt controller IC:
> 
> 	ic: interrupt-controller@...08000 {
> 		compatible = "foo";
> 		interrupt-controller;
> 		#interrupt-cells = <2>;
>                 ...
> 	};
> 
> And we have a user of this IC:
> 
> 	foo-peripheral@...48000 {
> 		compatible = "foo-peripheral";
> 		interrupt-parent = <&ic>;
> 		interrupts = <39 4>;
> 	};
> 
> Here first field of "interrupts" gives interrupt line number and the second one
> gives polarity, interrupt type etc..

So far so good.

> All is good till now. Now, every interrupt controller supports the first
> field, but the second one depends on its capabilities. An interrupt controller
> might not have registers to configure interrupt polarity, type, etc of
> the interrupt
> it will service and so the second field wouldn't be available for them.
> 
> For now just think stmpe is not a MFD and not a interrupt controller
> either. It is
> just a simple device, dev-foo.
> 
> It will declare values of its interrupts field based on the type of
> interrupt controller
> that will service its interrupt and that can be anything like VIC/GIC/GPIO
> controller.
> 
> Obviously nobody else than the parent IC driver can parse interrupts field
> of dev-foo, because only that driver understands the real meaning of
> these fields.
> 
> Now, stmpe has a special property. It can decide the way its output
> interrupt line
> will work. i.e. its polarity and interrupt type - edle/level, etc..
> This is not commonly
> seen in any peripheral. Now my original bindings and the real question here is
> about passing this information to stmpe driver.
> 
> I can't pass it in interrupts field of stmpe node, as that field
> belongs to parent
> interrupt controller of stmpe.
> 
> I can't pass that from child nodes of stmpe, as we are programming the interrupt
> coming out of stmpe and not the interrupt coming out of stmpe-gpio or
> stmpe-keypad.
> 
> And that's why i added these bindings. Please suggest me if i am still missing
> something.

Look into .xlate functions.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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