linux-kernel - Re: [linux-sunxi] Re: [PATCH 11/11] arm64: dts: add Pine64 support

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Date:	Tue, 9 Feb 2016 21:33:21 +0100
From:	Danny Milosavljevic <dannym@...atchpost.org>
To:	Julian Calaby <julian.calaby@...il.com>
Cc:	andre.przywara@....com,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Arnd Bergmann <arnd@...db.de>,
	"Mailing List, Arm" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	devicetree <devicetree@...r.kernel.org>
Subject: Re: [linux-sunxi] Re: [PATCH 11/11] arm64: dts: add Pine64 support

Hi,

On Mon, 8 Feb 2016 11:55:43 +1100
Julian Calaby <julian.calaby@...il.com> wrote:

> I believe that device tree overlays are the generally recommended method.

I agree. But last time I tried, the device tree compiler didn't 
support overlays - neither in Debian nor in the in-kernel dtc ("-@" is 
unsupported; last tried with linux-4.3-rc7). 

And even if you could compile them, the platform has to support specifying which 
overlays to use in the first place (for example as a Linux cmdline option). 

For example Beaglebone Black (TI Sitara) does. I don't know whether sunxi does.

Also, the overlay dts files are very different from normal dts files, see 
<http://www.patternagents.com/news/2015/01/29/devicetree-overlays.html>.

The original Linux device tree changeset patchset also introduced an in-kernel 
interface for loading/unloading of DT overlays at runtime. AFAIK, this is still 
not available to user space.

More info at <https://lwn.net/Articles/616859/>.

(I tried some 4 months ago - it wasn't integrated enough. 
 So now I just patch the main dts every time - which I probably shouldn't)

Regards,
   Danny