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 18:07:31 +0200
From:	Benoit Cousson <b-cousson@...com>
To:	Jon Hunter <jon-hunter@...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 05:59 PM, Jon Hunter wrote:
> 
> 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.

For consistency, I'd rather not add it at all for the moment.
Later, when we will only support DT boot, people will start complaining
about the boot time increase and then we will start optimizing a little
bit :-)

Regards,
Benoit


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