linux-kernel - Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

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Date:	Tue, 31 Jul 2012 20:22:17 +0800
From:	Mitch Bradley <wmb@...mworks.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
CC:	Alex Courbot <acourbot@...dia.com>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

On 7/31/2012 6:56 PM, Thierry Reding wrote:
> On Tue, Jul 31, 2012 at 07:32:20PM +0900, Alex Courbot wrote:
>> On 07/31/2012 07:45 AM, Stephen Warren wrote:
>>> I wonder if using the same structure/array as input and output would
>>> simplify the API; the platform data would fill in the fields mentioned
>>> above, and power_seq_build() would parse those, then set other fields in
>>> the same structs to the looked-up handle values?
>>
>> The thing is that I am not sure what happens to the platform data
>> once probe() is done. Isn't it customary to mark it with __devinit
>> and have it freed after probing is successful?
> 
> No, platform data should stay around forever. Otherwise, consider what
> would happen if your driver is built as a module and you unload and load
> it again.
> 
>> More generally, I think it is a good practice to have data
>> structures tailored right for what they need to do - code with
>> members that are meaningful only at given points of an instance's
>> life tends to be more confusing.
> 
> I agree. Furthermore the driver unload/reload would be another reason
> not to reuse platform data as the output of the build() function.
> 
> But maybe what Stephen meant was more like filling a structure with data
> taken from the platform data and pass that to a resolve() function which
> would fill in the missing pieces like pointers to actual resources. I
> imagine a managed interface would become a little trickier to do using
> such an approach.
> 
>>> If the nodes have a unit address (i.e. end in "@n"), which they will
>>> have to if all named "step" and there's more than one of them, then they
>>> will need a matching reg property. Equally, the parent node will need
>>> #address-cells and #size-cells too. So, the last couple lines would be:
>>>
>>> 		power-on-sequence {
>>> 			#address-cells = <1>;
>>> 			#size-cells = <0>;
>>> 			step@0 {
>>> 				reg = <0>;
>>
>> That's precisely what I would like to avoid - I don't need the steps
>> to be numbered and I certainly have no use for a reg property. Isn't
>> there a way to make it simpler?
> 
> It's not technically valid to not have the reg property. Or
> #address-cells and #size-cells properties for that matter.

I'm not keen on this representation where individual steps are nodes.
That seems like it could end up being too "heavyweight" for a long sequence.


> 
> Thierry
> 
> 
> 
> _______________________________________________
> devicetree-discuss mailing list
> devicetree-discuss@...ts.ozlabs.org
> https://lists.ozlabs.org/listinfo/devicetree-discuss
> 
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