mainboard/google/reef: add board SKU'ing support

There are 2 gpios on reef-like boards that can be composed
into a SKU. Add support for identifying the SKU value using
the base 3 gpio logic. Also export the SKU information to the
SMBIOS type 1 table.

BUG=chrome-os-partner:59887,chrome-os-partner:60494
BRANCH=reef

Change-Id: I8bb94207b0b7833d758054a817b655e248f1b239
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/17771
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/google/reef/mainboard.c

@@ -19,9 +19,12 @@
 #include <console/console.h>
 #include <device/device.h>
 #include <ec/ec.h>
+#include <gpio.h>
 #include <nhlt.h>
+#include <smbios.h>
 #include <soc/gpio.h>
 #include <soc/nhlt.h>
+#include <string.h>
 #include <vendorcode/google/chromeos/chromeos.h>
 #include <variant/ec.h>
 #include <variant/gpio.h>
@@ -41,6 +44,35 @@ static void mainboard_init(void *chip_info)
 	mainboard_ec_init();
 }
 
+/*
+ * There are 2 pins on reef-like boards that can be used for SKU'ing
+ * board differences. They each have optional stuffing for a pullup and
+ * a pulldown. This way we can generate 9 different values with the
+ * 2 pins.
+ */
+static int board_sku(void)
+{
+	static int board_sku_num = -1;
+	gpio_t board_sku_gpios[] = {
+		[1] = GPIO_17, [0] = GPIO_16,
+	};
+	const size_t num = ARRAY_SIZE(board_sku_gpios);
+
+	if (board_sku_num < 0)
+		board_sku_num = gpio_base3_value(board_sku_gpios, num);
+
+	return board_sku_num;
+}
+
+const char *smbios_mainboard_sku(void)
+{
+	static char sku_str[5]; /* sku[0-8] */
+
+	snprintf(sku_str, sizeof(sku_str), "sku%d", board_sku());
+
+	return sku_str;
+}
+
 void __attribute__((weak)) variant_nhlt_oem_overrides(const char **oem_id,
 						const char **oem_table_id,
 						uint32_t *oem_revision)