On Fri, Sep 28, 2018 at 8:42 PM Rob Herring [off-list ref] wrote:

On Fri, Sep 28, 2018 at 12:21 PM Andreas Färber [off-list ref] wrote:

quoted

Am 13.09.18 um 17:51 schrieb Geert Uytterhoeven:

quoted

On Wed, Sep 12, 2018 at 3:02 AM Masahiro Yamada
[off-list ref] wrote:

quoted

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.

quoted

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@linux-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