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

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Message-ID: <20120731105640.GD16155@avionic-0098.adnet.avionic-design.de>
Date:	Tue, 31 Jul 2012 12:56:40 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Stephen Warren <swarren@...dia.com>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...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 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.

Thierry

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