linux-kernel - Re: [PATCH v2 1/4] ARM: dts: omap5: Update GPIO with address space and interrupts

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Date:	Tue, 23 Oct 2012 10:59:06 -0500
From:	Jon Hunter <jon-hunter@...com>
To:	Benoit Cousson <b-cousson@...com>
CC:	Sebastien Guiriec <s-guiriec@...com>,
	Tony Lindgren <tony@...mide.com>,
	<devicetree-discuss@...ts.ozlabs.org>,
	<linux-omap@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/4] ARM: dts: omap5: Update GPIO with address space
 and interrupts


On 10/23/2012 10:09 AM, Benoit Cousson wrote:
> On 10/23/2012 04:49 PM, Jon Hunter wrote:
>> Hi Seb,
>>
>> On 10/23/2012 03:37 AM, Sebastien Guiriec wrote:
>>> Add base address and interrupt line inside Device Tree data for
>>> OMAP5
>>>
>>> Signed-off-by: Sebastien Guiriec <s-guiriec@...com>
>>> ---
>>>  arch/arm/boot/dts/omap5.dtsi |   16 ++++++++++++++++
>>>  1 file changed, 16 insertions(+)
>>>
>>> diff --git a/arch/arm/boot/dts/omap5.dtsi b/arch/arm/boot/dts/omap5.dtsi
>>> index 42c78be..9e39f9f 100644
>>> --- a/arch/arm/boot/dts/omap5.dtsi
>>> +++ b/arch/arm/boot/dts/omap5.dtsi
>>> @@ -104,6 +104,8 @@
>>>  
>>>  		gpio1: gpio@...10000 {
>>>  			compatible = "ti,omap4-gpio";
>>> +			reg = <0x4ae10000 0x200>;
>>> +			interrupts = <0 29 0x4>;
>>>  			ti,hwmods = "gpio1";
>>>  			gpio-controller;
>>>  			#gpio-cells = <2>;
>>
>> I am wondering if we should add the "interrupt-parent" property to add
>> nodes in the device-tree source. I know that today the interrupt-parent
>> is being defined globally, but when device-tree maps an interrupt for a
>> device it searches for the interrupt-parent starting the current device
>> node.
>>
>> So in other words, for gpio1 it will search the gpio1 binding for
>> "interrupt-parent" and if not found move up a level and search again. It
>> will keep doing this until it finds the "interrupt-parent".
>>
>> Therefore, I believe it will improve search time and hence, boot time if
>> we have interrupt-parent defined in each node.
> 
> Mmm, I'm not that sure. it will increase the size of the blob, so
> increase the time to load it and then to parse it. Where in the current
> case, it is just going up to the parent node using the already
> un-flatten tree in memory and thus that should not take that much time.

Yes it will definitely increase the size, so that could slow things down.

> That being said, it might be interesting to benchmark that to see what
> is the real impact.

Right, I wonder what the key functions are we need to benchmark to get
an overall feel for what is best? Right now I am seeing some people add
the interrupt-parent for device nodes and others not. Ideally we should
be consistent, but at the same time it is probably something that we can
easily sort out later. So not a big deal either way.

Cheers
Jon
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