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

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Message-ID: <50879C4E.6020003@ti.com>
Date:	Wed, 24 Oct 2012 09:44:14 +0200
From:	Benoit Cousson <b-cousson@...com>
To:	Sebastien Guiriec <s-guiriec@...com>
CC:	Jon Hunter <jon-hunter@...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 06:15 PM, Sebastien Guiriec wrote:
> Hi Benoit and John,
> 
> On 10/23/2012 06:07 PM, Benoit Cousson wrote:
>> 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 :-)
> 
> I just do it like that to be consistent with what is inside OMAP4 dtsi
> for those IPs (GPIO/UART/MMC/I2C). Now after checking Peter already add
> the interrupt-parent for all audio IPs (OMAP3/4/5). But here we need
> also interrupts name. So here we should try to be consistent.
> 
> So I can send back the series for OMAP5 and update the OMAP4 with
>   interrupts-parent = <&gic>

No, you should not, as explained previously. You'd better remove the one
already in audio IPs for consistency.


Regards,
Benoit

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