mfd: Add ChromeOS EC I2C driver

This uses an I2C bus to talk to the ChromeOS EC. The protocol
is defined by the EC and is fairly simple, with a length byte,
checksum, command byte and version byte (to permit easy creation
of new commands).

Signed-off-by: Simon Glass <[e-mail]>
Signed-off-by: Che-Liang Chiou <[e-mail]>
Signed-off-by: Samuel Ortiz <[e-mail]>

drivers/mfd/Kconfig

···
 	  You also ned to enable the driver for the bus you are using. The
 	  protocol for talking to the EC is defined by the bus driver.
 
+config MFD_CROS_EC_I2C
+	tristate "ChromeOS Embedded Controller (I2C)"
+	depends on MFD_CROS_EC && I2C
+
+	help
+	  If you say Y here, you get support for talking to the ChromeOS
+	  EC through an I2C bus. This uses a simple byte-level protocol with
+	  a checksum. Failing accesses will be retried three times to
+	  improve reliability.
+
 config MFD_88PM800
 	tristate "Support Marvell 88PM800"
 	depends on I2C=y && GENERIC_HARDIRQS

drivers/mfd/Makefile

···
 obj-$(CONFIG_MFD_SM501)		+= sm501.o
 obj-$(CONFIG_MFD_ASIC3)		+= asic3.o tmio_core.o
 obj-$(CONFIG_MFD_CROS_EC)	+= cros_ec.o
+obj-$(CONFIG_MFD_CROS_EC_I2C)	+= cros_ec_i2c.o
 
 rtsx_pci-objs			:= rtsx_pcr.o rts5209.o rts5229.o rtl8411.o rts5227.o
 obj-$(CONFIG_MFD_RTSX_PCI)	+= rtsx_pci.o

drivers/mfd/cros_ec_i2c.c

···
+/*
+ * ChromeOS EC multi-function device (I2C)
+ *
+ * Copyright (C) 2012 Google, Inc
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * 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.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/cros_ec.h>
+#include <linux/mfd/cros_ec_commands.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+static inline struct cros_ec_device *to_ec_dev(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+
+	return i2c_get_clientdata(client);
+}
+
+static int cros_ec_command_xfer(struct cros_ec_device *ec_dev,
+				struct cros_ec_msg *msg)
+{
+	struct i2c_client *client = ec_dev->priv;
+	int ret = -ENOMEM;
+	int i;
+	int packet_len;
+	u8 *out_buf = NULL;
+	u8 *in_buf = NULL;
+	u8 sum;
+	struct i2c_msg i2c_msg[2];
+
+	i2c_msg[0].addr = client->addr;
+	i2c_msg[0].flags = 0;
+	i2c_msg[1].addr = client->addr;
+	i2c_msg[1].flags = I2C_M_RD;
+
+	/*
+	 * allocate larger packet (one byte for checksum, one byte for
+	 * length, and one for result code)
+	 */
+	packet_len = msg->in_len + 3;
+	in_buf = kzalloc(packet_len, GFP_KERNEL);
+	if (!in_buf)
+		goto done;
+	i2c_msg[1].len = packet_len;
+	i2c_msg[1].buf = (char *)in_buf;
+
+	/*
+	 * allocate larger packet (one byte for checksum, one for
+	 * command code, one for length, and one for command version)
+	 */
+	packet_len = msg->out_len + 4;
+	out_buf = kzalloc(packet_len, GFP_KERNEL);
+	if (!out_buf)
+		goto done;
+	i2c_msg[0].len = packet_len;
+	i2c_msg[0].buf = (char *)out_buf;
+
+	out_buf[0] = EC_CMD_VERSION0 + msg->version;
+	out_buf[1] = msg->cmd;
+	out_buf[2] = msg->out_len;
+
+	/* copy message payload and compute checksum */
+	sum = out_buf[0] + out_buf[1] + out_buf[2];
+	for (i = 0; i < msg->out_len; i++) {
+		out_buf[3 + i] = msg->out_buf[i];
+		sum += out_buf[3 + i];
+	}
+	out_buf[3 + msg->out_len] = sum;
+
+	/* send command to EC and read answer */
+	ret = i2c_transfer(client->adapter, i2c_msg, 2);
+	if (ret < 0) {
+		dev_err(ec_dev->dev, "i2c transfer failed: %d\n", ret);
+		goto done;
+	} else if (ret != 2) {
+		dev_err(ec_dev->dev, "failed to get response: %d\n", ret);
+		ret = -EIO;
+		goto done;
+	}
+
+	/* check response error code */
+	if (i2c_msg[1].buf[0]) {
+		dev_warn(ec_dev->dev, "command 0x%02x returned an error %d\n",
+			 msg->cmd, i2c_msg[1].buf[0]);
+		ret = -EINVAL;
+		goto done;
+	}
+
+	/* copy response packet payload and compute checksum */
+	sum = in_buf[0] + in_buf[1];
+	for (i = 0; i < msg->in_len; i++) {
+		msg->in_buf[i] = in_buf[2 + i];
+		sum += in_buf[2 + i];
+	}
+	dev_dbg(ec_dev->dev, "packet: %*ph, sum = %02x\n",
+		i2c_msg[1].len, in_buf, sum);
+	if (sum != in_buf[2 + msg->in_len]) {
+		dev_err(ec_dev->dev, "bad packet checksum\n");
+		ret = -EBADMSG;
+		goto done;
+	}
+
+	ret = 0;
+ done:
+	kfree(in_buf);
+	kfree(out_buf);
+	return ret;
+}
+
+static int cros_ec_probe_i2c(struct i2c_client *client,
+			     const struct i2c_device_id *dev_id)
+{
+	struct device *dev = &client->dev;
+	struct cros_ec_device *ec_dev = NULL;
+	int err;
+
+ 	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
+	if (!ec_dev)
+		return -ENOMEM;
+
+	i2c_set_clientdata(client, ec_dev);
+	ec_dev->name = "I2C";
+	ec_dev->dev = dev;
+	ec_dev->priv = client;
+	ec_dev->irq = client->irq;
+	ec_dev->command_xfer = cros_ec_command_xfer;
+	ec_dev->ec_name = client->name;
+	ec_dev->phys_name = client->adapter->name;
+	ec_dev->parent = &client->dev;
+
+	err = cros_ec_register(ec_dev);
+	if (err) {
+		dev_err(dev, "cannot register EC\n");
+		return err;
+	}
+
+	return 0;
+}
+
+static int cros_ec_remove_i2c(struct i2c_client *client)
+{
+	struct cros_ec_device *ec_dev = i2c_get_clientdata(client);
+
+	cros_ec_remove(ec_dev);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int cros_ec_i2c_suspend(struct device *dev)
+{
+	struct cros_ec_device *ec_dev = to_ec_dev(dev);
+
+	return cros_ec_suspend(ec_dev);
+}
+
+static int cros_ec_i2c_resume(struct device *dev)
+{
+	struct cros_ec_device *ec_dev = to_ec_dev(dev);
+
+	return cros_ec_resume(ec_dev);
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(cros_ec_i2c_pm_ops, cros_ec_i2c_suspend,
+			  cros_ec_i2c_resume);
+
+static const struct i2c_device_id cros_ec_i2c_id[] = {
+	{ "cros-ec-i2c", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, cros_ec_i2c_id);
+
+static struct i2c_driver cros_ec_driver = {
+	.driver	= {
+		.name	= "cros-ec-i2c",
+		.owner	= THIS_MODULE,
+		.pm	= &cros_ec_i2c_pm_ops,
+	},
+	.probe		= cros_ec_probe_i2c,
+	.remove		= cros_ec_remove_i2c,
+	.id_table	= cros_ec_i2c_id,
+};
+
+module_i2c_driver(cros_ec_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ChromeOS EC multi function device");