[PATCH v5.5] of/fdt: export fdt blob as /sys/firmware/fdt

On Tue, Nov 18, 2014 at 4:11 PM, Grant Likely [off-list ref] wrote:

On Tue, 18 Nov 2014 17:25:45 +0000
, Mark Rutland [off-list ref]
 wrote:

quoted

On Tue, Nov 18, 2014 at 04:51:45PM +0000, Grant Likely wrote:

quoted

On Fri, 14 Nov 2014 18:05:35 +0100
, Ard Biesheuvel [off-list ref]
 wrote:

quoted

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.

[...]

quoted

quoted

* It also helps with exposing the reserved map to userspace, but kexec
  has done without that feature for years, and it is in the process of
  being deprecated in favour of /reserved-memory anyway.

This is the first I'd heard of the reserve map being deprecated, and
we're going to have DTs with reserved map entries for a long time going
forwards.

Deprecated, not removed or disabled. It will still work pretty much
forever, but users should be encouraged to move to the reserve-memory
tree.

I thought you had said reserve map was still the right way for memory
the kernel should never touch.

quoted

Can't we expose the header fields under something like
/sys/firmware/devicetree/dtb-header/, parallel to the usual
/sys/firmware/devicetree/base for nodes?

We could do that too.

Honestly though, I'm just unsure of what the best thing to do is. If you
and a few others tell me that, "no, exporting the raw dtb is the right
thing to do", then I'll be okay, merge the patch and sleep properly.

I always sleep better when others can take the blame.

What happens when we rev the dtb format? Is the ABI the blob or the
format of the blob?

I lean towards we should add this. This is providing what is "in the
firmware" while /proc/devicetree provides the live tree state
including overlays.

Rob