linux-kernel - Re: [PATCH v2] of: document /sys/firmware/fdt

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Date:   Wed, 28 Jun 2017 14:57:59 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] of: document /sys/firmware/fdt

Hi Rob,

Please ignore this version, Grant replied to your v1 comment, so
I'll spin a v3.

-Frank

On 06/28/17 14:53, frowand.list@...il.com wrote:
> From: Frank Rowand <frank.rowand@...y.com>
> 
> Add ABI documentation for /sys/firmware/fdt
> 
> Change obsolete contact for /sys/firmware/devicetree/* to mail list
> 
> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
> ---
> 
> changes from v1:
>   - Remove obsolete email address as contact for /sys/firmware/devicetree/*
>   - For newly documented /sys/firmware/fdt do not include any individual
>     email for Contact (only provide email list)
> 
>  Documentation/ABI/testing/sysfs-firmware-ofw | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-firmware-ofw b/Documentation/ABI/testing/sysfs-firmware-ofw
> index f562b188e71d..30a6b3621828 100644
> --- a/Documentation/ABI/testing/sysfs-firmware-ofw
> +++ b/Documentation/ABI/testing/sysfs-firmware-ofw
> @@ -1,6 +1,6 @@
>  What:		/sys/firmware/devicetree/*
>  Date:		November 2013
> -Contact:	Grant Likely <grant.likely@...aro.org>
> +Contact:	devicetree@...r.kernel.org
>  Description:
>  		When using OpenFirmware or a Flattened Device Tree to enumerate
>  		hardware, the device tree structure will be exposed in this
> @@ -26,3 +26,28 @@ Description:
>  		name plus address). Properties are represented as files
>  		in the directory. The contents of each file is the exact
>  		binary data from the device tree.
> +
> +What:		/sys/firmware/fdt
> +Date:		February 2015
> +KernelVersion:	3.19
> +Contact:	devicetree@...r.kernel.org
> +Description:
> +		Exports the FDT blob that was passed to the kernel by
> +		the bootloader. This allows userland applications such
> +		as kexec to access the raw binary. This blob is also
> +		useful when debugging since it contains any changes
> +		made to the blob by the bootloader.
> +
> +		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.
> +
> +		A CRC32 checksum is calculated over the entire FDT
> +		blob, and verified at late_initcall time. The sysfs
> +		entry is instantiated only if the checksum is valid,
> +		i.e., if the FDT blob has not been modified in the mean
> +		time. Otherwise, a warning is printed.
> +Users:		kexec, debugging
> +
>