Re: [PATCH 4/5] firmware: Add coreboot device tree binding documentation

Mark Rutland
2017-03-24T12:22:54Z

On Thu, Mar 23, 2017 at 10:04:28PM +0100, Thierry Escande wrote:
> From: Julius Werner <jwerner@chromium.org>
>
> This patch adds documentation describing a device tree binding for the
> coreboot firmware. It is meant to be dynamically added during boot and
> contains address definitions for the coreboot table (a list of
> variable-sized descriptors providing information about various compile-
> and run-time generated firmware parameters) and the CBMEM area (the
> structure containing most run-time resident memory regions set up by
> coreboot).
>
> These definitions allow kernel drivers to easily access data contained
> in and pointed to by these regions (such as coreboot's in-memory log).
> (An example implementation can be seen in the following patch)
>
> Signed-off-by: Julius Werner <jwerner@chromium.org>
> Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
> ---
> .../devicetree/bindings/firmware/coreboot.txt | 33 ++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/firmware/coreboot.txt
>
> diff --git a/Documentation/devicetree/bindings/firmware/coreboot.txt b/Documentation/devicetree/bindings/firmware/coreboot.txt
> new file mode 100644
> index 0000000..4c95570
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/coreboot.txt
> @@ -0,0 +1,33 @@
> +COREBOOT firmware information
> +
> +The device tree node to communicate the location of coreboot's memory-resident
> +bookkeeping structures to the kernel. Since coreboot itself cannot boot a
> +device-tree-based kernel (yet), this node needs to be inserted by a
> +second-stage bootloader (a coreboot "payload").
> +
> +Required properties:
> + - compatible: Should be "coreboot"

Devicetree bindings should be in vendor,prefix format. This doesn't
represent every aspect of coreboot, so it needs a more descriptive
string.

> + - reg: Address and length of the following two memory regions, in order:
> + 1.) The coreboot table. This is a list of variable-sized descriptors
> + that contain various compile- and run-time generated firmware
> + parameters. It is identified by the magic string "LBIO" in its first
> + four bytes.
> + See coreboot's src/commonlib/include/commonlib/coreboot_tables.h for
> + details.

Given this is a memory region, it should be described under the
reserved-memory node.

> + 2.) The CBMEM area. This is a downward-growing memory region used by
> + coreboot to dynamically allocate data structures that remain resident.
> + It may or may not include the coreboot table as one of its members. It
> + is identified by a root node descriptor with the magic number
> + 0xc0389481 that resides in the topmost 8 bytes of the area.
> + See coreboot's src/include/imd.h for details.

I beleive likewise here.

Thanks,
Mark.

> +
> +Example:
> + firmware {
> + ranges;
> +
> + coreboot {
> + compatible = "coreboot";
> + reg = <0xfdfea000 0x264>,
> + <0xfdfea000 0x16000>;
> + }
> + };
> --
> 2.7.4
>
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