i2c: Add software_i2c driver for I2C debugging and emulation

This patch adds I2C emulation in software through raw toggling of the
SDA/SCL lines. Platforms need to provide bindings to toggle their
respective I2C busses for this to work (e.g. by pinmuxing them as GPIOs,
currently only enabled for Tegra).

This is mostly useful as a debugging feature, to drive unusual states on
a bus and closely monitor the device output without the need of a bus
analyzer. It provides a few functions to "wedge" an I2C bus by aborting
a transaction at certain points, which can be used to test if a system
can correctly recover from an ill-timed reboot. However, it can also
dynamically replace the existing I2C transfer functions and drive
some/all I2C transfers on the system, which might be useful if a driver
for the actual I2C controller hardware is not (yet) available.

Based on original code by Doug Anderson <dianders@chromium.org> and
Hung-ying Tyan <tyanh@chromium.org> for the ChromeOS embedded
controller project.

BRANCH=None
BUG=chrome-os-partner:28323
TEST=Spread tegra_software_i2c_init()/tegra_software_i2c_disable()
through the code and see that everything still works.

Original-Change-Id: I9ee7ccbd1efb38206669a35d0c3318af16f8be63
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/198791
Original-Reviewed-by: Doug Anderson <dianders@chromium.org>
Original-Reviewed-by: Tom Warren <twarren@nvidia.com>
Original-Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
(cherry picked from commit 8f71503dbbd74c5298e90e2163b67d4efe3e89db)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: Id6c5f75bb5baaabd62b6b1fc26c2c71d9f1ce682
Reviewed-on: http://review.coreboot.org/7947
Tested-by: build bot (Jenkins)
Reviewed-by: David Hendricks <dhendrix@chromium.org>

3 files changed, 99 insertions, 1 deletions

diff --git a/src/soc/nvidia/tegra/i2c.c b/src/soc/nvidia/tegra/i2c.c
index 6c269cfaed..555d0318c1 100644
--- a/src/soc/nvidia/tegra/i2c.c
+++ b/src/soc/nvidia/tegra/i2c.c
@@ -180,7 +180,7 @@ static int i2c_transfer_segment(unsigned bus, unsigned chip, int restart,
 	return 0;
 }
 
-int i2c_transfer(unsigned bus, struct i2c_seg *segments, int count)
+int platform_i2c_transfer(unsigned bus, struct i2c_seg *segments, int count)
 {
 	struct i2c_seg *seg = segments;
 
diff --git a/src/soc/nvidia/tegra/i2c.h b/src/soc/nvidia/tegra/i2c.h
index 6347fff8ad..4b1bddd2af 100644
--- a/src/soc/nvidia/tegra/i2c.h
+++ b/src/soc/nvidia/tegra/i2c.h
@@ -23,6 +23,8 @@
 #include <stdint.h>
 
 void i2c_init(unsigned bus);
+void tegra_software_i2c_init(unsigned bus);
+void tegra_software_i2c_disable(unsigned bus);
 
 enum {
 	/* Word 0 */
diff --git a/src/soc/nvidia/tegra/software_i2c.c b/src/soc/nvidia/tegra/software_i2c.c
new file mode 100644
index 0000000000..b50fb4f654
--- /dev/null
+++ b/src/soc/nvidia/tegra/software_i2c.c
@@ -0,0 +1,96 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 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 <device/i2c.h>
+#include <soc/nvidia/tegra124/gpio.h>
+#include <soc/nvidia/tegra124/pinmux.h>
+
+#include "i2c.h"
+
+static struct {
+	int pinmux_func;
+	gpio_t sda;
+	gpio_t scl;
+} pins[] = {
+	[0]{.pinmux_func = PINMUX_GEN1_I2C_SCL_FUNC_I2C1,
+	    .sda = GPIO(C5), .scl = GPIO(C4)},
+	[1]{.pinmux_func = PINMUX_GEN2_I2C_SCL_FUNC_I2C2,
+	    .sda = GPIO(T6), .scl = GPIO(T5)},
+	[2]{.pinmux_func = PINMUX_CAM_I2C_SCL_FUNC_I2C3,
+	    .sda = GPIO(BB2), .scl = GPIO(BB1)},
+	[3]{.pinmux_func = PINMUX_DDC_SCL_FUNC_I2C4,
+	    .sda = GPIO(V5), .scl = GPIO(V4)},
+	[4]{.pinmux_func = PINMUX_PWR_I2C_SCL_FUNC_I2CPMU,
+	    .sda = GPIO(Z7), .scl = GPIO(Z6)},
+};
+
+static void tegra_set_sda(unsigned bus, int high)
+{
+	if (high)
+		gpio_input_pullup(pins[bus].sda);
+	else
+		gpio_output(pins[bus].sda, 0);
+}
+
+static void tegra_set_scl(unsigned bus, int high)
+{
+	if (high)
+		gpio_input_pullup(pins[bus].scl);
+	else
+		gpio_output(pins[bus].scl, 0);
+}
+
+static int tegra_get_sda(unsigned bus)
+{
+	return gpio_get_in_value(pins[bus].sda);
+}
+
+static int tegra_get_scl(unsigned bus)
+{
+	return gpio_get_in_value(pins[bus].scl);
+}
+
+static struct software_i2c_ops tegra_ops = {
+	.set_sda = tegra_set_sda,
+	.set_scl = tegra_set_scl,
+	.get_sda = tegra_get_sda,
+	.get_scl = tegra_get_scl,
+};
+
+void tegra_software_i2c_init(unsigned bus)
+{
+	software_i2c[bus] = &tegra_ops;
+
+	/* Initialize bus to idle state. */
+	tegra_set_sda(bus, 1);
+	tegra_set_scl(bus, 1);
+}
+
+void tegra_software_i2c_disable(unsigned bus)
+{
+	software_i2c[bus] = NULL;
+
+	/* Return pins to I2C controller. */
+	pinmux_set_config(pins[bus].sda >> GPIO_PINMUX_SHIFT,
+			  pins[bus].pinmux_func | PINMUX_INPUT_ENABLE);
+	pinmux_set_config(pins[bus].scl >> GPIO_PINMUX_SHIFT,
+			  pins[bus].pinmux_func | PINMUX_INPUT_ENABLE);
+	gpio_set_mode(pins[bus].sda, GPIO_MODE_SPIO);
+	gpio_set_mode(pins[bus].scl, GPIO_MODE_SPIO);
+}