Generalize revision number calculation function

Some platforms use tertiary interpretation of GPIO input state to
increase number of distinct values represented by a limited number of
GPIOs. The three states are

- external pull down (interpreted as 0)
- external pull up (1)
- not connected (2)

This has been required by Nvidia devices so far, but Exynos and
Ipq8086 platforms need this too.

This patch moves the function reading the tertiary state into the
library and exposes the necessary GPIO API functions in a new include
file. The functions are still supposed to be provided by platform
specific modules.

The function interpreting the GPIO states has been modified to allow
to interpret the state either as a true tertiary number or as a set
two bit fields.

Since linker garbage collection is not happening when building x86
targets, a new configuration option is being added to include the new
module only when needed.

BUG=chrome-os-partner:30489
TEST=verified that nyan_big still reports proper revision ID.

Change-Id: Ib55122c359629b58288c1022da83e6c63dc2264d
Original-Change-Id: I243c9f43c82bd4a41de2154bbdbd07df0a241046
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/209673
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
(cherry picked from commit c79ef1c545d073eaad69e6c8c629f9656b8c2f3e)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-on: http://review.coreboot.org/8717
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/src/lib/tristate_gpios.c b/src/lib/tristate_gpios.c
new file mode 100644
index 0000000000..b1ebbc0f71
--- /dev/null
+++ b/src/lib/tristate_gpios.c
@@ -0,0 +1,79 @@
+/*
+ * 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 <delay.h>
+#include <gpiolib.h>
+
+int gpio_board_id(gpio_t gpio[], int num_gpio, int tertiary)
+{
+	/*
+	 * 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.
+	 */
+
+	int temp;
+	int index;
+	int id = 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_in_value(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
+	 */
+	for (index = 0; index < num_gpio; ++index) {
+		if (tertiary)
+			id *= 3;
+		else
+			id <<= 2;
+		temp = gpio_get_in_value(gpio[index]);
+		id += ((value[index] ^ temp) << 1) | temp;
+	}
+
+	/* Disable pull up / pull down to conserve power */
+	for (index = 0; index < num_gpio; ++index)
+		gpio_input(gpio[index]);
+
+	return id;
+}