linux-kernel - Re: Using device tree overlays in Linux

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Message-ID: <85be88b38c79424d84ee2499b5ab81fc@svr-chch-ex1.atlnz.lc>
Date:   Tue, 9 Apr 2019 20:54:03 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Frank Rowand <frowand.list@...il.com>,
        "pantelis.antoniou@...sulko.com" <pantelis.antoniou@...sulko.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
CC:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hamish Martin <Hamish.Martin@...iedtelesis.co.nz>
Subject: Re: Using device tree overlays in Linux

On 10/04/19 7:19 AM, Frank Rowand wrote:
> On 4/7/19 6:27 PM, Chris Packham wrote:
>> Hi Frank,
>>
>> On 8/04/19 1:05 PM, Frank Rowand wrote:
>>> Hi Chris,
>>>
>>> On 4/3/19 6:50 PM, Chris Packham wrote:
>>>> Hi,
>>>>
>>>> I'm implementing support for some modular Linux based systems using
>>>> device tree overlays. The code is working but it seems a little more
>>>> fiddly that than it should be so I'm wondering if I'm doing it right.
>>>
>>> Let me start by saying that I strongly discourage using device tree
>>> overlays in the Linux kernel until the support is more baked.  For
>>> some info on how unbaked overlays are, see:
>>>
>>>      https://elinux.org/Frank%27s_Evolving_Overlay_Thoughts
>>>
>>> You should consider applying overlays in the Linux kernel to be
>>> fragile at best.
>>>
>>> If you can not figure out how to solve your needs without using
>>> overlays, then having the boot loader apply the overlay instead
>>> of the kernel applying the overlay avoids most of the issues.
>>>
>>
>> Consider us beta-testers :).
> 
> You should read the elinux.org page more carefully.  The support
> isn't even alpha stage.  It is at the level of proof of concept.
> 
> I'll update that page to explicitly say the code is proof of
> concept.

pre-alpha-testers then. We've actually been using the early overlay 
support for a while and it's suited our needs quite well. Aside from the 
internal API changes as we move to the latest kernel the current support 
also seems to meet our needs.

Both Hamish and I are quite keen to see this move forward so please 
don't hesitate to ask us if there are things we might be able to help 
with. Even if it's just trying something out on our hardware platforms.