soc/intel/common: Add LPSS I2C driver

Add a generic LPSS I2C driver for Intel SOCs that use the Synopsys
DesignWare I2C block and have a similar configuration of that block.

This driver is ported from the Chromium depthcharge project where it
was ported from U-Boot originally, though it looks very different now.
From depthcharge it has been modified to fit into the coreboot I2C
driver model with platform_i2c_transfer() and use coreboot semantics
throughout including the stopwatch API for timeouts.

In order for this shared driver to work the SOC must:

1) Define CONFIG_SOC_INTEL_COMMON_LPSS_I2C_CLOCK_MHZ to set the clock
speed that the I2C controller core is running at.

2) Define the lpss_i2c_base_address() function to return the base
address for the specified bus.  This could be either done by looking
up the PCI device or a static table if the controllers are not PCI
devices and just have a static base address.

The driver is usable in verstage/romstage/ramstage, though it does
require early initialization of the controller to set a temporary base
address if it is used outside of ramstage.

This has been tested on Broadwell and Skylake SOCs in both pre-RAM and
ramstage environments by reading and writing both single bytes across
multiple segments as well as large blocks of data at once and with
different configured bus speeds.

While it does need specific configuration for each SOC this driver
should be able to work on all Intel SOCs currently in src/soc/intel.

Change-Id: Ibe492e53c45edb1d1745ec75e1ff66004081717e
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/15101
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/common/lpss_i2c.h

@@ -0,0 +1,41 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2016 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.
+ */
+
+#ifndef SOC_INTEL_COMMON_LPSS_I2C_H
+#define SOC_INTEL_COMMON_LPSS_I2C_H
+
+#include <device/i2c.h>
+#include <stdint.h>
+
+/*
+ * Return the base address for this bus controller.
+ *
+ * This function *must* be implemented by the SOC and return the appropriate
+ * base address for the I2C registers that correspond to the provided bus.
+ */
+uintptr_t lpss_i2c_base_address(unsigned bus);
+
+/*
+ * Initialize this bus controller and set the speed.
+ *
+ * The bus speed can be passed in Hz or using values from device/i2c.h and
+ * will default to I2C_SPEED_FAST if it is not provided.
+ *
+ * The SOC *must* define CONFIG_SOC_INTEL_COMMON_LPSS_I2C_CLOCK for the
+ * bus speed calculation to be correct.
+ */
+void lpss_i2c_init(unsigned bus, enum i2c_speed speed);
+
+#endif