coreboot-kgpe-d16/src/mainboard/google/storm/boardid.c

/* SPDX-License-Identifier: GPL-2.0-only */

#include <boardid.h>
#include <gpio.h>
#include <console/console.h>

/*
 * Storm boards dedicate to the board ID three GPIOs in tertiary mode: 29, 30
 * and 68. On proto0 GPIO68 is used and tied low, so it reads as 'zero' by
 * gpio_base3_value(), whereas the other two pins are not connected
 * and read as 'two'. This results in gpio_base3_value() returning
 * 8 on proto0.
 *
 * Three tertitiary signals could represent 27 different values. To make
 * calculated board ID value continuous and starting at zero, offset the
 * calculated value by 19 (i.e. 27 - 8) and return modulo 27 of the offset
 * number. This results in proto0 returning zero as the board ID, the future
 * revisions will have the inputs configured to match the actual board
 * revision.
 */

static int board_id_value = -1;

static uint8_t get_board_id(void)
{
	uint8_t bid;
	gpio_t hw_rev_gpios[] = {[2] = 68, [1] = 30, [0] = 29};	/* 29 is LSB */
	int offset = 19;

	bid = gpio_base3_value(hw_rev_gpios, ARRAY_SIZE(hw_rev_gpios));
	bid = (bid + offset) % 27;
	printk(BIOS_INFO, "Board ID %d\n", bid);

	return bid;
}

uint32_t board_id(void)
{
	if (board_id_value < 0)
		board_id_value = get_board_id();

	return board_id_value;
}