First draft of PSA interruptible ECC signing design

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/include/psa/crypto_values.h b/include/psa/crypto_values.h
index ee95745..07e96f7 100644
--- a/include/psa/crypto_values.h
+++ b/include/psa/crypto_values.h
@@ -335,6 +335,13 @@
  */
 #define PSA_ERROR_DATA_INVALID          ((psa_status_t)-153)
 
+/** The function that returns this status is defined as interruptible and
+ *  still has work to do, thus the user should call the function again with the
+ *  same operation context until it either returns #PSA_SUCCESS or any other
+ *  error. This is not an error per se, more a notification of status.
+ */
+#define PSA_OPERATION_INCOMPLETE           ((psa_status_t)-248)
+
 /* *INDENT-ON* */
 
 /**@}*/
@@ -2739,4 +2746,18 @@
 
 /**@}*/
 
+/**@}*/
+
+/** \defgroup interruptible Interruptible operations
+ * @{
+ */
+
+/** Maximum value for use with \c psa_interruptible_set_max_ops() to determine
+ *  the maximum number of ops allowed to be executed by an interruptible
+ *  function in a single call.
+ */
+#define PSA_INTERRUPTIBLE_MAX_OPS_UNLIMITED INT32_MAX
+
+/**@}*/
+
 #endif /* PSA_CRYPTO_VALUES_H */