linux-kernel - Re: [PATCH v3 6/9] kbuild: consolidate Devicetree dtb build rules

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Message-ID: <CAMuHMdW_+PNZrh5JXo8MxVwg3YSZL7bszMcUJjCqMFfBz8HDPQ@mail.gmail.com>
Date:   Mon, 1 Oct 2018 09:53:15 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Andreas Färber <afaerber@...e.de>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Michal Simek <monstr@...str.eu>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        arcml <linux-snps-arc@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:H8/300 ARCHITECTURE" 
        <uclinux-h8-devel@...ts.sourceforge.jp>,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        nios2-dev@...ts.rocketboards.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-xtensa@...ux-xtensa.org, Will Deacon <will.deacon@....com>,
        Paul Burton <paul.burton@...s.com>, ley.foon.tan@...el.com
Subject: Re: [PATCH v3 6/9] kbuild: consolidate Devicetree dtb build rules

On Fri, Sep 28, 2018 at 8:42 PM Rob Herring <robh@...nel.org> wrote:
> On Fri, Sep 28, 2018 at 12:21 PM Andreas Färber <afaerber@...e.de> wrote:
> > Am 13.09.18 um 17:51 schrieb Geert Uytterhoeven:
> > > On Wed, Sep 12, 2018 at 3:02 AM Masahiro Yamada
> > > <yamada.masahiro@...ionext.com> wrote:
> > >> Even x86 can enable OF and OF_UNITTEST.
> > >>
> > >> Another solution might be,
> > >> guard it by 'depends on ARCH_SUPPORTS_OF'.
> > >>
> > >> This is actually what ACPI does.
> > >>
> > >> menuconfig ACPI
> > >>         bool "ACPI (Advanced Configuration and Power Interface) Support"
> > >>         depends on ARCH_SUPPORTS_ACPI
> > >>          ...
> > >
> > > ACPI is a real platform feature, as it depends on firmware.
> > >
> > > CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform,
> > > even if it has ACPI ;-)
> >
> > How would loading a DT overlay work on an ACPI platform? I.e., what
> > would it overlay against and how to practically load such a file?
>
> The DT unittests do just that. I run them on x86 and UM builds. In
> this case, the loading source is built-in.
>
> > I wonder whether that could be helpful for USB devices and serdev...
>
> How to load the overlays is pretty orthogonal to the issues to be
> solved here. It would certainly be possible to move forward with
> prototyping this and just have the overlay built-in. It may not even
> need to be an overlay if we can support multiple root nodes.

You indeed need to refer to some anchors for most use cases, although a
simple MMIO device could just be anchored to the root node.

Topologies hanging off a USB device would be my first use case, too,
for serdev, or for e.g. the mcp2210 USB-SPI bridge.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds