doc: cmd: add documentation for sm3sum

add documentation for sm3sum command.

Signed-off-by: Heiko Schocher <hs@nabladev.com>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

doc/usage/cmd/sm3sum.rst

@@ -0,0 +1,112 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+.. Copyright Nabla Software Engineering GmbH
+   Written by Heiko Schocher <hs@nabladev.com>
+
+.. index::
+   single: sm3sum (command)
+
+sm3sum command
+==============
+
+Synopsis
+--------
+
+::
+
+    sm3sum - compute SM3 message digest
+
+    Usage:
+    sm3sum address count [[*]sum]
+      - compute SM3 message digest [save to sum]
+    sm3sum -v address count [*]sum
+      - verify sm3sum of memory area
+
+
+Description
+-----------
+
+The sm3sum command calculates the SM3 hash of data of ``count`` bytes
+at address ``address``. If the ``-v`` option is passed to the command,
+it compares the calculated hash with the hash found at address ``sum``.
+
+The SM3 secure hash is calculated as specified by OSCCA GM/T
+0004-2012 SM3 and described at
+
+https://datatracker.ietf.org/doc/html/draft-sca-cfrg-sm3-02
+
+Parameters
+----------
+
+address
+    address from where the sm3 hash is calculated.
+    Hexadecimal string, 0x prefix optional.
+
+count
+    length in bytes of memory area for which the sm3 hash is calculated
+    Hexadecimal string, 0x prefix optional.
+
+sum
+    if it starts with ``*`` the string is interpreted as an address
+    in hexadecimal format to which the calculated hash gets stored.
+
+    else the string is interpreted as a name for an environment variable
+    in which the calculated hash is stored as string.
+
+    or if ``-v`` option is passed:
+
+    address of hash with which the calculated hash gets compared.
+
+Example
+-------
+
+create some data
+
+::
+
+    u-boot=> mw 0x100000000 0x426f6f46 1
+    u-boot=> md.b 0x100000000 4
+    00000000: 46 6f 6f 42                                      FooB
+
+and calculate the sm3sum of 4 bytes starting from address ``0x100000000``
+and store it in environment variable ``hashval``
+
+::
+
+    u-boot=> sm3sum 0x100000000 4 hashval
+    sm3_256 for 100000000 ... 100000003 ==> cdf49da4e33017bf2d9fe87b885d80c9a7c920be7e10ffb8c89036a1eb1503b7
+    u-boot=> print hashval
+    hashval=cdf49da4e33017bf2d9fe87b885d80c9a7c920be7e10ffb8c89036a1eb1503b7
+    u-boot=>
+
+or calculate sm3sum of 4 bytes starting from address ``0x100000000`` and
+store it at address ``0x110000000``
+
+::
+
+    u-boot=> sm3sum 0x100000000 4 *0x110000000
+    sm3_256 for 100000000 ... 100000003 ==> cdf49da4e33017bf2d9fe87b885d80c9a7c920be7e10ffb8c89036a1eb1503b7
+
+and now check if this hash is the expected sm3sum hash value with ``-v``
+option
+
+::
+
+    u-boot=> sm3sum -v 0x100000000 4 *0x110000000
+    u-boot=> echo $?
+    0
+
+example with wrong hash
+
+::
+
+    u-boot=> sm3sum -v 0x100000000 4 *0x110000004
+    sm3_256 for 100000000 ... 100000003 ==> cdf49da4e33017bf2d9fe87b885d80c9a7c920be7e10ffb8c89036a1eb1503b7 != e33017bf2d9fe87b885d80c9a7c920be7e10ffb8c89036a1eb1503b7ffffffff ** ERROR **
+    u-boot=>
+
+
+Configuration
+-------------
+
+Enable the sm3sum command via Kconfig option ``CONFIG_CMD_SM3SUM``.
+The ``-v`` option is separate enabled through Kconfig option
+``CONFIG_SM3SUM_VERIFY``.