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

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Date:   Wed, 28 Jun 2017 14:53:57 -0700
From:   frowand.list@...il.com
To:     Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] of: document /sys/firmware/fdt

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
+
-- 
Frank Rowand <frank.rowand@...y.com>