Message-Id: <10734BE8-4135-4381-A6CB-478188E6E50E@antoniou-consulting.com>
Date:	Fri, 8 Nov 2013 09:12:18 +0200
From:	Pantelis Antoniou <panto@...oniou-consulting.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <robherring2@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Matt Porter <matt.porter@...aro.org>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Alison Chaiken <Alison_Chaiken@...tor.com>,
	Dinh Nguyen <dinh.linux@...il.com>,
	Jan Lubbe <jluebbe@...net.de>,
	Alexander Sverdlin <alexander.sverdlin@....com>,
	Michael Stickel <ms@...able.de>,
	Dirk Behme <dirk.behme@...il.com>,
	Alan Tull <delicious.quinoa@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Michael Bohan <mbohan@...eaurora.org>,
	Ionut Nicu <ioan.nicu.ext@....com>,
	Michal Simek <monstr@...str.eu>,
	Matt Ranostay <mranostay@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3 - V2] Introducing Device Tree Overlays

Hi Guenter,

On Nov 8, 2013, at 1:00 AM, Guenter Roeck wrote:

> On Thu, Nov 07, 2013 at 09:46:26PM +0100, Sebastian Andrzej Siewior wrote:
>> On 07.11.13, Pantelis Antoniou wrote:
>>> Hi Sebastian,
>> Hi Pantelis,
>> 
>>> FWIW DT has been ported to x86. And is present on arm/powerpc/mips/arc and possibly
>>> others.
>> 
>> Yes, I know. I am the one that did the work for CE4100, the first one
>> that boots with DT on x86.
>> 
>>> So what are we talking about again? If you care about the non-DT case, why
>>> don't you make a patch about how you could support Guenter's use case on
>>> the x86.
>> 
>> I am only saying that this "hot-plug a device at a non hot-plugagle bus at
>> runtime" is not limited to DT but this solution is. X86 + ACPI is not
>> the only limitation. ARM is (forced) going to ACPI as well as far I
>> know. And this solution is limited to DT. This is what I am pointing
>> out.
>> 
> I can't tell about ARM, but I am not entirely sure how ACPI support on ARM
> is going to help us on powerpc.
> 
>>> His use case is not uncommon, believe it or not, and x86 would benefit from
>>> something this flexible.
>> 
>> I *think* a more flexible solution would be something like bus_type which is
>> exposed via configfs. It would be attached behind a certain device/bus where
>> the "physical" hotplug interface is. The user would then be able to read the
>> configuration based on whatever information he has and could then create
>> devices he likes at runtime. This wouldn't depend much on the firmware that is
>> used but would require a little more work I think.
>> 
> Quite frankly, I am interested at a solution that works and solves our problems.
> I am not looking for something that is 100% perfect and may never be delivered.
> 

+1

> Fortunately, the Linux kernel was willing to adopt multiple different file
> systems, and still accepts new ones on a regular basis. If a new file system
> is better, it will start getting used, and old file systems are being phased out
> as fewer people use them. I would hope the same should be possible with DT
> overlays and possible other future solutions for the same problem, and that
> we won't have to wait for the perfect solution from day 1.
> 

Fully agreed here. I was told open source is about scratching an itch, this
is worthy of scratching.

> Guenter

Regards

-- Pantelis

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