linux-kernel - Re: [PATCH] of: provide of_platform

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Date:	Wed, 31 Jul 2013 17:21:58 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	Rob Herring <robherring2@...il.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	George Cherian <george.cherian@...com>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	devicetree-discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Naveen Krishna Chatradhi <ch.naveen@...sung.com>,
	Roger Quadros <rogerq@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
Subject: Re: [PATCH] of: provide of_platform_unpopulate()

* Grant Likely | 2013-07-24 15:19:58 [+0100]:

>> Was there more breakage than imx6 and amba devices? Your first version
>> had a fallback case for powerpc. Couldn't we do just allow that for more
>> than just powerpc? I'd much rather see some work-around within the core
>> DT code with a warning to prevent more proliferation than putting this
>> into drivers.
>
>It's tricky stuff. I've not figured out a solution I'm happy with.
>Trying to figure out when to apply a work around is hard because the
>resource reservation makes assumptions about the memory range layout
>that doesn't match the assumptions made by device tree code.

I can't really follow. Do you have a simple at hand?

>One /possible/ option is to not add the resources to the devices at all
>when the device is registered and instead resolve them right at bind
>time. Jean Christophe proposed doing this already to solve a different
>problem; obtaining resources that require other drivers to be probed
>first. If the resources are resolved at .probe() time, then the resource
>registration problem should also go away.
>
>The downside to that approach is that it makes each deferred probe more
>expensive; potentially a *lot* more expensive depending on how much work
>the xlate functions have to do. It would be worth prototyping though to
>see how well it works.

So you say defer the io ressources until the device-tree device is
actually probed. I don't really understand why that defer part should
solve the problem but I would try and see how it goes.
Jean-Christophe proposed that only, that means no patches yet, right?

>g.

Sebastian
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