linux-kernel - Re: [PATCH] external references for device tree overlays

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Date:   Wed, 7 Jun 2017 17:19:33 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Cc:     Stefani Seibold <stefani@...bold.net>,
        Stefani Seibold <stefani.seibold.ext@...wei.com>,
        Frank Rowand <frowand.list@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Holm Rauchfuss <holm.rauchfuss@...wei.com>
Subject: Re: [PATCH] external references for device tree overlays

On Wed, Jun 7, 2017 at 3:11 AM, Pantelis Antoniou
<pantelis.antoniou@...sulko.com> wrote:
> Hi Stefani,
>
> On Tue, 2017-06-06 at 21:17 +0200, Stefani Seibold wrote:
>> Hi Pantelis,
>>
>> thanks for the suggestion. This feature is not very well documented. I
>> tried this on my rasp1 running 4.12.0-rc3 and it doesn't work. My
>> source is:
>>
>> // rapsi example
>> /dts-v1/;
>> /plugin/;
>>
>> / {
>>     compatible = "brcm,bcm2835", "brcm,bcm2708", "brcm,bcm2709";
>>
>>     fragment@0 {
>>         target-path = "/soc/i2s@...03000";
>>         __overlay__ {
>>             #address-cells = <0x00000001>;
>>             #size-cells = <0x00000001>;
>>             test = "test";
>>             timer = <&{/soc/timer@...030000}>;
>>         };
>>     };
>> };
>>
>>
>> The resulting overlay is (decompiled with fdtdump):
>>
>> /dts-v1/;
>> // magic:             0xd00dfeed
>> // totalsize:         0x19a (410)
>> // off_dt_struct:     0x38
>> // off_dt_strings:    0x148
>> // off_mem_rsvmap:    0x28
>> // version:           17
>> // last_comp_version: 16
>> // boot_cpuid_phys:   0x0
>> // size_dt_strings:   0x52
>> // size_dt_struct:    0x110
>>
>> / {
>>     compatible = "brcm,bcm2835", "brcm,bcm2708", "brcm,bcm2709";
>>     fragment@0 {
>>         target-path = "/soc/i2s@...03000";
>>         __overlay__ {
>>             #address-cells = <0x00000001>;
>>             #size-cells = <0x00000001>;
>>             test = "test";
>>             timer = <0xdeadbeef>;
>>         };
>>     };
>>     __fixups__ {
>>         /soc/timer@...030000 = "/fragment@..._overlay__:timer:0";
>>     };
>> };
>>
>> But this will not apply:
>>
>> OF: resolver: overlay phandle fixup failed: -22
>> create_overlay: Failed to resolve tree
>>
>>
>
> Yes, it will not work as it is; my point is that you don't need the
> magic __*__ node.
>
> You will need to modify the overlay application code to live insert a
> phandle (if it doesn't exist) when it encounters a /path fixup.

phandles only exist if something in the base tree refers to that node.
Adding them when they don't exist should definitely be something we
support for overlays. But don't call that a broken DT. That would be a
separate issue.

Rob