Re: [PATCH] drivers/of: add option to load a default Device Tree

From: Pantelis Antoniou <panto-wVdstyuyKrO8r51toPun2/C9HSW9iNxf@public.gmane.org>
To: Franck Jullien <franck.jullien-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Frank Rowand
	<frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Franck Jullien
	<franck.jullien-EduPiq9onwdphFt5fpzH3laPQRlvutdw@public.gmane.org>,
	devicetree <devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	jose.abreu-HKixBCOQz3hWk0Htik3J/w@public.gmane.org,
	Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>
Subject: Re: [PATCH] drivers/of: add option to load a default Device Tree
Date: Thu, 30 Jun 2016 23:46:10 +0300	[thread overview]
Message-ID: <FC6DF2EE-CE1A-4EEB-BCD6-ECCE04F680A8@antoniou-consulting.com> (raw)
In-Reply-To: <CAJfOKByav-r9=4YEJrzuCfeAyTEtr4+=a_0d08gSLBSRrPPiEA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

Hi Franck,

> On Jun 30, 2016, at 23:44 , Franck Jullien <franck.jullien-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 
> 2016-06-30 19:45 GMT+02:00 Frank Rowand <frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
>> Hi Franck,
>> 
>> (This could be confusing, with Franck and Frank -- feel free to
>> address me as rowand in this thread if it is less confusing.)
>> 
>> On 06/22/16 08:05, Franck Jullien wrote:
>>> Even if a platform doesn't use a device tree during its
>>> boot process it can be useful to enable CONFIG_OF and get
>>> an empty device tree.
>>> 
>>> Then, devices can use device tree overlays to populate this
>>> default tree.
>>> 
>>> Signed-off-by: Franck Jullien <franck.jullien-EduPiq9onwdphFt5fpzH3laPQRlvutdw@public.gmane.org>
>>> ---
>>> drivers/of/Kconfig     |  9 +++++++++
>>> drivers/of/Makefile    |  3 +++
>>> drivers/of/base.c      | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>> drivers/of/default.dts |  4 ++++
>>> drivers/of/unittest.c  | 33 +++++----------------------------
>>> include/linux/of.h     |  2 ++
>>> 6 files changed, 73 insertions(+), 28 deletions(-)
>>> create mode 100644 drivers/of/default.dts
>> 
>> < snip >
>> 
>> For context, in a later reply, you mention that this is for x86_64.
>> 
>> My current inclination is to prefer not to solve the problem this way.
>> I was going to ask why you didn't just add the compiled default.dts
>> to the kernel as an appended device tree blob, until I found out
>> this was for x86_64.
>> 
>> Can you add unflatten_devicetree() to x86_64, then just use the
>> appended device tree blob method?
>> 
> 
> You're saying I should implement the ability for x86_64 to detect and
> load a devicetree that is appended to the binary image like ARM does [1] ?
> 
> Would you keep CONFIG_DEFAULT_DTB at all ? Or appending an
> empty (or not) devicetree would be after the binary image is built ?
> 
> I like the idea. I think I could remove CONFIG_DEFAULT_DTB and
> let the user append a blob to the image.
> 
> By the way, why having an empty devicetree built-in is not your
> preferred choice ?
> 

Already have a patch that does that but it needs some cleanup. I haven’t bothered
with the i386 version either.

Sigh, -ENOTIME..

> Franck.
> 

Regards

— Pantelis

> [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=e2a6a3aafa9862c4a4b59f2a59b8f923d64a680e

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