linux-kernel - Re: [PATCH] of: Kconfig: OF_OVERLAY, select OF_EARLY

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Date:   Sun, 18 Feb 2018 19:46:46 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Pantelis Antoniou <panto@...oniou-consulting.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH] of: Kconfig: OF_OVERLAY, select OF_EARLY_FLATTREE

On Sun, Feb 18, 2018 at 6:29 PM,  <frowand.list@...il.com> wrote:
> From: Frank Rowand <frank.rowand@...y.com>
>
> kbuild test robot reported a new warning for a recent patch:
>>> drivers/of/overlay.c:832:2: error: implicit declaration of function 'of_fdt_unflatten_tree' [-Werror=implicit-function-declaration]
>      of_fdt_unflatten_tree(new_fdt, NULL, &overlay_root);
>
> The cause is that the prototype for of_fdt_unflatten_tree() in
> include/linux/of_fdt.c is guarded by OF_EARLY_FLATTREE.
>
> This was a pre-existing problem for any overlay related caller of
> of_fdt_unflatten_device_tree(), who was then going to pass the
> unflattened tree to of_overlay_apply().  After the patch that triggered
> this warning, all other overlay callers of of_fdt_unflatten_device_tree()
> no longer exist, so adding the select to OF_OVERLAY is a sufficient fix.
>
> To reproduce the warning:
>   Use the .config attached to https://lkml.org/lkml/2018/2/17/268
>   make ARCH=i386 olddefconfig
>   make ARCH=i386 CC=gcc-7 drivers/of/overlay.o
>
> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
> ---
>  drivers/of/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 783e0870bd22..00a6abfaaec7 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -92,6 +92,7 @@ config OF_RESOLVE
>  config OF_OVERLAY
>         bool "Device Tree overlays"
>         select OF_DYNAMIC
> +       select OF_EARLY_FLATTREE

If we do this, we might as well kill OF_EARLY_FLATTREE. What platform
really boots from not FDT, but uses DT without overlays?

Rob