[PATCH] of/fdt: export fdt blob as /sys/firmware/fdt

Arnd Bergmann arnd at arndb.de
Mon Nov 10 10:02:03 PST 2014

On Monday 10 November 2014 18:08:03 Ard Biesheuvel wrote:
> On 10 November 2014 17:57, Arnd Bergmann <arnd at arndb.de> wrote:
> > On Monday 10 November 2014 17:51:45 Ard Biesheuvel wrote:
> >> Create a new /sys entry '/sys/firmware/fdt' to export the FDT blob
> >> that was passed to the kernel by the bootloader. This allows userland
> >> applications such as kexec to access the raw binary.
> >>
> >> The fact that this node does not reside under /sys/firmware/device-tree
> >> is deliberate: FDT is also used on arm64 UEFI/ACPI systems to
> >> communicate just the UEFI and ACPI entry points, but the FDT is never
> >> unflattened and used to configure the system.
> >>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> >
> > Can you elaborate on the motivation? Initially the fdt format was
> > introduced to make it easy to pass the information from /proc/device-tree
> > to the next kernel for kexec. Are you interested in cases where this does
> > not work?
> >
> /sys/firmware/device-tree only gets populated if you are really
> booting in DT mode, i.e., when the device tree is unflattened.
> However, in ACPI mode we still need to access the data that was
> communicated between UEFI and the kernel in the /chosen node if we
> want to support kexec under UEFI.

Ah, now I get it.


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