doc: add opal secure variable documentation

This patch contains the work-in-progress documentation for the
secure variable design in OPAL. Future revisions of this patch
set will (hopefully) add new pieces of documentation here.

Signed-off-by: Eric Richter <erichte@linux.ibm.com>
[oliver: whitespace error fixes, removed old backend node docs]
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
---
V3:
 - removed metadata
 - removed get_size
 - updated _get semantics for size queries
 - added/expanded device tree properties

V4:
 - updated for new device tree changes

V5:
 - removed incorrect ibm,secureboot changes
 - rewrote bindings using a different format
 - moved secvar documentation under ibm,opal

V6:
 - moved os-secureboot-enforcing to ibm,secureboot
 - removed backend node from secvar node
 - updated documentation on secvar node compatible

1 files changed, 192 insertions, 0 deletions

diff --git a/doc/opal-api/opal-secvar.rst b/doc/opal-api/opal-secvar.rst
new file mode 100644
index 0000000..f07c570
--- /dev/null
+++ b/doc/opal-api/opal-secvar.rst
@@ -0,0 +1,192 @@
+OPAL Secure Variable API
+========================
+
+Overview
+--------
+
+In order to support host OS secure boot on POWER systems, the platform needs
+some form of tamper-resistant persistant storage for authorized public keys.
+Furthermore, these keys must be retrieveable by the host kernel, and new
+keys must be able to be submitted.
+
+OPAL exposes an abstracted "variable" API, in which these keys can be stored
+and retrieved. At a high level, ``opal_secvar_get`` retrieves a specific
+variable corresponding to a particular key. ``opal_secvar_get_next`` can be
+used to iterate through the keys of the stored variables.
+``opal_secvar_enqueue_update`` can be used to submit a new variable for
+processing on next boot.
+
+OPAL_SECVAR_GET
+===============
+::
+
+   #define OPAL_SECVAR_GET                         176
+
+``OPAL_SECVAR_GET`` call retrieves a data blob associated with the supplied
+key.
+
+
+Parameters
+----------
+::
+
+   char     *key
+   uint64_t  key_len
+   void     *data
+   uint64_t *data_size
+
+``key``
+   a buffer used to associate with the variable data. May
+be any encoding, but must not be all zeroes
+
+``key_len``
+   size of the key buffer in bytes
+
+``data``
+   return buffer to store the data blob of the requested variable if
+a match was found. May be set to NULL to only query the size into
+``data_size``
+
+``data_size``
+   reference to the size of the ``data`` buffer. OPAL sets this to
+the size of the requested variable if found.
+
+
+Return Values
+-------------
+
+``OPAL_SUCCESS``
+   the requested data blob was copied successfully. ``data`` was NULL,
+and the ``data_size`` value was set successfully
+
+``OPAL_PARAMETER``
+   ``key`` is NULL.
+   ``key_len`` is zero.
+   ``data_size`` is NULL.
+
+``OPAL_EMPTY``
+   no variable with the supplied ``key`` was found
+
+``OPAL_PARTIAL``
+   the buffer size provided in ``data_size`` was insufficient.
+``data_size`` is set to the minimum required size.
+
+``OPAL_UNSUPPORTED``
+   secure variables are not supported by the platform
+
+``OPAL_RESOURCE``
+   secure variables are supported, but did not initialize properly
+
+OPAL_SECVAR_GET_NEXT
+====================
+::
+
+   #define OPAL_SECVAR_GET_NEXT                        177
+
+``OPAL_SECVAR_GET_NEXT`` returns the key of the next variable in the secure
+variable bank in sequence.
+
+Parameters
+----------
+::
+
+   char     *key
+   uint64_t *key_len
+   uint64_t  key_buf_size
+
+
+``key``
+   name of the previous variable or empty. The key of the next
+variable in sequence will be copied to ``key``. If passed as empty,
+returns the first variable in the bank
+
+``key_len``
+   length in bytes of the key in the  ``key`` buffer. OPAL sets
+this to the length in bytes of the next variable in sequence
+
+``key_buf_size``
+   maximum size of the ``key`` buffer. The next key will not be
+copied if this value is less than the length of the next key
+
+
+Return Values
+-------------
+
+``OPAL_SUCCESS``
+   the key and length of the next variable in sequence was copied
+successfully
+
+``OPAL_PARAMETER``
+   ``key`` or ``key_length`` is NULL.
+   ``key_size`` is zero.
+   ``key_length`` is impossibly large. No variable with the associated
+``key`` was found
+
+``OPAL_EMPTY``
+   end of list reached
+
+``OPAL_PARTIAL``
+   the size specified in ``key_size`` is insufficient for the next
+variable's key length. ``key_length`` is set to the next variable's
+length, but ``key`` is untouched
+
+``OPAL_UNSUPPORTED``
+   secure variables are not supported by the platform
+
+``OPAL_RESOURCE``
+   secure variables are supported, but did not initialize properly
+
+OPAL_SECVAR_ENQUEUE_UPDATE
+==========================
+::
+
+   #define OPAL_SECVAR_ENQUEUE_UPDATE                    178
+
+``OPAL_SECVAR_ENQUEUE`` call appends the supplied variable data to the
+queue for processing on next boot.
+
+Parameters
+----------
+::
+
+   char     *key
+   uint64_t  key_len
+   void     *data
+   uint64_t  data_size
+
+``key``
+   a buffer used to associate with the variable data. May
+be any encoding, but must not be all zeroes
+
+``key_len``
+   size of the key buffer in bytes
+
+``data``
+   buffer containing the blob of data to enqueue
+
+``data_size``
+   size of the ``data`` buffer
+
+Return Values
+-------------
+
+``OPAL_SUCCESS``
+   the variable was appended to the update queue bank successfully
+
+``OPAL_PARAMETER``
+   ``key`` or ``data`` was NULL.
+   ``key`` was empty.
+   ``key_len`` or ``data_size`` was zero.
+   ``key_len``, ``data_size`` is larger than the maximum size
+
+``OPAL_NO_MEM``
+   OPAL was unable to allocate memory for the variable update
+
+``OPAL_HARDWARE``
+   OPAL was unable to write the update to persistant storage
+
+``OPAL_UNSUPPORTED``
+   secure variables are not supported by the platform
+
+``OPAL_RESOURCE``
+   secure variables are supported, but did not initialize properly