linux-kernel - Re: [PATCH 0/3 - V2] Introducing Device Tree Overlays

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Date:	Thu, 07 Nov 2013 10:45:58 +0100
From:	Alexander Sverdlin <alexander.sverdlin@....com>
To:	ext Pantelis Antoniou <panto@...oniou-consulting.com>,
	Sebastian Andrzej Siewior <bigeasy@...akpoint.cc>
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>, Michael Stickel <ms@...able.de>,
	Guenter Roeck <linux@...ck-us.net>,
	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!

On 06/11/13 20:08, ext Pantelis Antoniou wrote:
>>> The following patchset introduces Device Tree overlays, a method
>>> of dynamically altering the kernel's live Device Tree, along with
>>> a generic interface to use it in a board agnostic manner.
>>
>> In case this has been discussed and I missed it: Why are we doing this?
>> Isn't it possible to d o the overlay thingy in u-boot and pass a
>> complete device tree to the kernel?
>> Are you trying to do something like hotplug-PCI where the PCI card can
>> be replaced at runtime?
>>
> 
> It has been discussed.
> 
> We are doing it because
> 
> a) We tried to do it in u-boot and it has been a complete disaster.
> Regular users just can't handle bootloader updates.

There are buses we simply do not want to deal with in uboot, like SRIO, PCIe, everything-over-ethernet.
All of them are hot-pluggable. And yeah, device-tree processing in uboot is possible, but in Linux
it's way easier...
 
> b) It is similar to that. It was originally created for the beaglebone,
> which has a concept of capes (similar to Arduino shields).
> http://circuitco.com/support/index.php?title=BeagleBone_Capes
> Turns out it's really useful to anyone doing reconfigurable hardware too,
> so that's why FPGA people are thinking of using it.
> 
> c) There are people that want to tinker with Linux based hardware boards
> but are not kernel developers. This gives them a way to do so without
> having to recompile the kernel and/or reboot while tinkering.
>  
>> Sebastian
> 
> Regards
> 
> -- Pantelis
> 
> 
> 

-- 
Best regards,
Alexander Sverdlin.
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