chromeos: Implement locating and decoding wifi sar data from VPD

A VPD entry "wifi_sar" needs to be created which contains a heximal
encoded string in length of 40 bytes. get_wifi_sar_limits() function
retrieves and decodes the data from the VPD entry, which would later
be consumed by platform code.

BUG=chrome-os-partner:60821
TEST=Build and boot lars and reef

Change-Id: I923b58a63dc1f8a7fdd685cf1c618b2fdf4e7061
Signed-off-by: Robbie Zhang <robbie.zhang@intel.com>
Reviewed-on: https://review.coreboot.org/17958
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/sar.h

@@ -0,0 +1,38 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2017 Intel Corp.
+ *
+ * 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 _SAR_H_
+#define _SAR_H_
+
+#include <stdint.h>
+
+#define NUM_SAR_LIMITS 4
+#define BYTES_PER_SAR_LIMIT 10
+
+/* Wifi SAR limit table structure */
+struct wifi_sar_limits {
+	/* Total 4 SAR limit sets, each has 10 bytes */
+	uint8_t sar_limit[NUM_SAR_LIMITS][BYTES_PER_SAR_LIMIT];
+};
+
+/*
+ * Retrieve the SAR limits data from VPD and decode it.
+ * sar_limits:	Pointer to wifi_sar_limits where the resulted data is stored
+ *
+ * Returns:	0 on success, -1 on errors (The VPD entry doesn't exist, or the
+ * VPD entry contains non-heximal value.)
+ */
+int get_wifi_sar_limits(struct wifi_sar_limits *sar_limits);
+
+#endif /* _SAR_H_ */

src/vendorcode/google/chromeos/Makefile.inc

@@ -25,6 +25,7 @@ ramstage-$(CONFIG_CHROMEOS_RAMOOPS) += ramoops.c
 romstage-y += vpd_decode.c
 ramstage-y += vpd_decode.c cros_vpd.c vpd_mac.c vpd_serialno.c vpd_calibration.c
 ramstage-$(CONFIG_HAVE_REGULATORY_DOMAIN) += wrdd.c
+ramstage-$(CONFIG_USE_SAR) += sar.c
 ifeq ($(CONFIG_ARCH_MIPS),)
 bootblock-y += watchdog.c
 ramstage-y += watchdog.c

src/vendorcode/google/chromeos/cros_vpd.h

@@ -8,6 +8,7 @@
 #define __CROS_VPD_H__
 
 #define CROS_VPD_REGION_NAME "region"
+#define CROS_VPD_WIFI_SAR_NAME "wifi_sar"
 
 /*
  * Reads VPD string value by key.

src/vendorcode/google/chromeos/sar.c

@@ -0,0 +1,60 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2017 Intel Corp.
+ *
+ * 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.
+ */
+#include <console/console.h>
+#include <types.h>
+#include <string.h>
+#include <sar.h>
+#include "cros_vpd.h"
+
+/* Retrieve the wifi SAR limits data from VPD and decode it */
+int get_wifi_sar_limits(struct wifi_sar_limits *sar_limits)
+{
+	const char *wifi_sar_limit_key = CROS_VPD_WIFI_SAR_NAME;
+	/*
+	 * cros_vpd_gets() reads in one less than size characters from the VPD
+	 * with a terminating null byte ('\0') stored as the last character into
+	 * the buffer, thus the increasing by 1 for buffer_size.
+	 */
+	const size_t buffer_size = (sizeof(struct wifi_sar_limits) /
+				    sizeof(uint8_t)) * 2 + 1;
+	char wifi_sar_limit_str[buffer_size];
+	uint8_t bin_buffer[sizeof(struct wifi_sar_limits)];
+
+	/* Try to read the SAR limit entry from VPD */
+	if (!cros_vpd_gets(wifi_sar_limit_key, wifi_sar_limit_str,
+		ARRAY_SIZE(wifi_sar_limit_str))) {
+		printk(BIOS_ERR,
+			"Error: Could not locate '%s' in VPD\n",
+			wifi_sar_limit_key);
+		return -1;
+	}
+	printk(BIOS_DEBUG, "VPD wifi_sar = %s\n", wifi_sar_limit_str);
+
+	/* Decode the heximal encoded string to binary values */
+	if (hexstrtobin(wifi_sar_limit_str, bin_buffer,
+			sizeof(struct wifi_sar_limits))
+			< sizeof(struct wifi_sar_limits)) {
+		printk(BIOS_ERR,
+			"Error: VPD wifi_sar contains non-heximal value!\n");
+		return -1;
+	}
+
+	/* Fill the sar_limits structure with the decoded data */
+	for (int i = 0; i < NUM_SAR_LIMITS; i++)
+		memcpy(sar_limits->sar_limit[i],
+			&bin_buffer[BYTES_PER_SAR_LIMIT * i],
+			BYTES_PER_SAR_LIMIT);
+	return 0;
+}