smmstore: Add a key/val store facility in flash, mediated through SMM

It exposes an interface that is as generic as possible, so payloads
and/or kernels can use it for their data.

Change-Id: I9553922f9dfa60b9d4b3576973ad4b84d3fe2fb5
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/25182
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/smmstore.h

@@ -0,0 +1,52 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2018 The Chromium OS Authors.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef _SMMSTORE_H_
+#define _SMMSTORE_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#define SMMSTORE_APM_CNT 0xed
+
+#define SMMSTORE_RET_SUCCESS 0
+#define SMMSTORE_RET_FAILURE 1
+#define SMMSTORE_RET_UNSUPPORTED 2
+
+#define SMMSTORE_CMD_CLEAR 1
+#define SMMSTORE_CMD_READ 2
+#define SMMSTORE_CMD_APPEND 3
+
+struct smmstore_params_read {
+	void *buf;
+	ssize_t bufsize;
+};
+
+struct smmstore_params_append {
+	void *key;
+	size_t keysize;
+	void *val;
+	size_t valsize;
+};
+
+/* SMM responder */
+uint32_t smmstore_exec(uint8_t command, void *param);
+
+/* implementation */
+int smmstore_read_region(void *buf, ssize_t *bufsize);
+int smmstore_append_data(void *key, uint32_t key_sz,
+	void *value, uint32_t value_sz);
+int smmstore_clear_region(void);
+#endif