gpio: cosmetic changes to tristate_gpios.c

This patch makes a few cosmetic changes:
- Rename tristate_gpios.c to gpio.c since it will soon be used for
  binary GPIOs as well.
- Rename gpio_get_tristates() to gpio_base3_value() - The binary
  version will be called gpio_base2_value().
- Updates call sites.
- Change the variable name "id" to something more generic.

BUG=none
BRANCH=none
TEST=compiled for veyron_pinky and storm

Change-Id: Iab7e32f4e9d70853f782695cfe6842accff1df64
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: c47d0f33ea1a6e9515211b834009cf47a171953f
Original-Change-Id: I36d88c67cb118efd1730278691dc3e4ecb6055ee
Original-Signed-off-by: David Hendricks <dhendrix@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/228324
Reviewed-on: http://review.coreboot.org/9411
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/lib/gpio.c

@@ -0,0 +1,82 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2014 Google Inc.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <base3.h>
+#include <console/console.h>
+#include <delay.h>
+#include <gpio.h>
+
+int gpio_base3_value(gpio_t gpio[], int num_gpio)
+{
+	/*
+	 * GPIOs which are tied to stronger external pull up or pull down
+	 * will stay there regardless of the internal pull up or pull
+	 * down setting.
+	 *
+	 * GPIOs which are floating will go to whatever level they're
+	 * internally pulled to.
+	 */
+
+	static const char tristate_char[] = {[0] = '0', [1] = '1', [Z] = 'Z'};
+	int temp;
+	int index;
+	int result = 0;
+	char value[num_gpio];
+
+	/* Enable internal pull up */
+	for (index = 0; index < num_gpio; ++index)
+		gpio_input_pullup(gpio[index]);
+
+	/* Wait until signals become stable */
+	udelay(10);
+
+	/* Get gpio values at internal pull up */
+	for (index = 0; index < num_gpio; ++index)
+		value[index] = gpio_get(gpio[index]);
+
+	/* Enable internal pull down */
+	for (index = 0; index < num_gpio; ++index)
+		gpio_input_pulldown(gpio[index]);
+
+	/* Wait until signals become stable */
+	udelay(10);
+
+	/*
+	 * Get gpio values at internal pull down.
+	 * Compare with gpio pull up value and then
+	 * determine a gpio final value/state:
+	 *  0: pull down
+	 *  1: pull up
+	 *  2: floating
+	 */
+	printk(BIOS_DEBUG, "Reading tristate GPIOs: ");
+	for (index = num_gpio - 1; index >= 0; --index) {
+		temp = gpio_get(gpio[index]);
+		temp |= ((value[index] ^ temp) << 1);
+		printk(BIOS_DEBUG, "%c ", tristate_char[temp]);
+		result = (result * 3) + temp;
+	}
+	printk(BIOS_DEBUG, "= %d\n", result);
+
+	/* Disable pull up / pull down to conserve power */
+	for (index = 0; index < num_gpio; ++index)
+		gpio_input(gpio[index]);
+
+	return result;
+}