Re: [PATCH v4 2/8] OF: Introduce DT overlay support.

From: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
To: Sebastian Reichel <sre@ring0.de>
Cc: Grant Likely <grant.likely@secretlab.ca>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Rob Herring <robherring2@gmail.com>,
	Stephen Warren <swarren@wwwdotorg.org>,
	Matt Porter <matt.porter@linaro.org>,
	Koen Kooi <koen@dominion.thruhere.net>,
	Alison Chaiken <Alison_Chaiken@mentor.com>,
	Dinh Nguyen <dinh.linux@gmail.com>, Jan Lubbe <jluebbe@lasnet.de>,
	Alexander Sverdlin <alexander.sverdlin@nsn.com>,
	Michael Stickel <ms@mycable.de>,
	Guenter Roeck <linux@roeck-us.net>,
	Dirk Behme <dirk.behme@gmail.com>,
	Alan Tull <delicious.quinoa@gmail.com>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Michael Bohan <mbohan@codeaurora.org>,
	Ionut Nicu <ioan.nicu.ext@nsn.com>,
	Michal Simek <monstr@monstr.eu>,
	Matt Ranostay <mranostay@gmail.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Pete Popov <pete.popov@konsulko.com>,
	Dan Malek <dan.malek@konsulko.com>,
	Georgi Vlaev <georgi.vlaev@konsulko.com>
Subject: Re: [PATCH v4 2/8] OF: Introduce DT overlay support.
Date: Mon, 26 May 2014 18:14:52 +0300	[thread overview]
Message-ID: <D9B0A90F-F089-48B1-926C-87689889AF42@konsulko.com> (raw)
In-Reply-To: <20140526150942.GA26787@earth.universe>

Hi Sebastian,

On May 26, 2014, at 6:09 PM, Sebastian Reichel wrote:

> Hi,
> 
> On Mon, May 26, 2014 at 02:55:37PM +0300, Pantelis Antoniou wrote:
>> On May 26, 2014, at 2:23 PM, Grant Likely wrote:
>>> On Mon, 26 May 2014 12:57:32 +0200, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>> Heeheehee. We're back where we started. The original question is whether
>>> or not that is a valid approach. If the overlay represents something
>>> that can be hot plugged/unplugged, then passing it through to the second
>>> kernel would be the wrong thing to do. If it was a permenant addition,
>>> then it probably doesn't need to be removed.
>>> 
>>> We do actually keep the overlay info in memory for the purpose of
>>> removal exactly so we can support hot unbinding of devices and drivers
>>> that make use of overlays.
>> 
>> We can support either method. I am not feeling any wiser about which one should be
>> the default TBH, so what about exporting a property and let the platform 
>> figure out which is more appropriate?
> 
> What about supporting "negative" overlays (so an overlay, that
> removes DT entries)? That way one could reverse apply an overlay.
> All the dependency stuff would basically be the users problem.  The
> kernel only checks if it can apply an overlay (and return some error
> code if it can't). This this code is needed anyway to check the
> input from userspace.
> 
> As a result the overlay handling would basically have the same
> behaviour as diff and patch :)
> 

This is already supported; nodes and properties can be prefixed with a minus
sign '-' and operate as expected :)

i.e. "-property;" removes a property and "-node { };" removes a node. 

> P.S.: Sorry if this has already been suggested. I have only read
> mails from PATCHv4.
> 
> -- Sebastian

Regards

-- Pantelis