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

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Date:   Fri, 24 Mar 2017 12:21:46 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Thierry Escande <thierry.escande@...labora.com>
Cc:     Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Olof Johansson <olof@...om.net>,
        Stephen Warren <swarren@...dia.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Julius Werner <jwerner@...omium.org>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH 4/5] firmware: Add coreboot device tree binding
 documentation

On Thu, Mar 23, 2017 at 10:04:28PM +0100, Thierry Escande wrote:
> From: Julius Werner <jwerner@...omium.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@...omium.org>
> Signed-off-by: Thierry Escande <thierry.escande@...labora.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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