platform/chrome: cros_ec: Add EC host command support using rpmsg

Add EC host command support through rpmsg.

Signed-off-by: Pi-Hsun Shih <[e-mail]>
Signed-off-by: Enric Balletbo i Serra <[e-mail]>

drivers/platform/chrome/Kconfig

···
 	  a checksum. Failing accesses will be retried three times to
 	  improve reliability.
 
+config CROS_EC_RPMSG
+	tristate "ChromeOS Embedded Controller (rpmsg)"
+	depends on MFD_CROS_EC && RPMSG && OF
+	help
+	  If you say Y here, you get support for talking to the ChromeOS EC
+	  through rpmsg. This uses a simple byte-level protocol with a
+	  checksum. Also since there's no addition EC-to-host interrupt, this
+	  use a byte in message to distinguish host event from host command.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cros_ec_rpmsg.
+
 config CROS_EC_SPI
 	tristate "ChromeOS Embedded Controller (SPI)"
 	depends on MFD_CROS_EC && SPI

drivers/platform/chrome/Makefile

···
 obj-$(CONFIG_CHROMEOS_PSTORE)		+= chromeos_pstore.o
 obj-$(CONFIG_CHROMEOS_TBMC)		+= chromeos_tbmc.o
 obj-$(CONFIG_CROS_EC_I2C)		+= cros_ec_i2c.o
+obj-$(CONFIG_CROS_EC_RPMSG)		+= cros_ec_rpmsg.o
 obj-$(CONFIG_CROS_EC_SPI)		+= cros_ec_spi.o
 cros_ec_lpcs-objs			:= cros_ec_lpc.o cros_ec_lpc_reg.o
 cros_ec_lpcs-$(CONFIG_CROS_EC_LPC_MEC)	+= cros_ec_lpc_mec.o

drivers/platform/chrome/cros_ec_rpmsg.c

···
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright 2018 Google LLC.
+
+#include <linux/completion.h>
+#include <linux/delay.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mfd/cros_ec.h>
+#include <linux/mfd/cros_ec_commands.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/rpmsg.h>
+#include <linux/slab.h>
+
+#define EC_MSG_TIMEOUT_MS	200
+#define HOST_COMMAND_MARK	1
+#define HOST_EVENT_MARK		2
+
+/**
+ * struct cros_ec_rpmsg_response - rpmsg message format from from EC.
+ *
+ * @type:	The type of message, should be either HOST_COMMAND_MARK or
+ *		HOST_EVENT_MARK, representing that the message is a response to
+ *		host command, or a host event.
+ * @data:	ec_host_response for host command.
+ */
+struct cros_ec_rpmsg_response {
+	u8 type;
+	u8 data[] __aligned(4);
+};
+
+/**
+ * struct cros_ec_rpmsg - information about a EC over rpmsg.
+ *
+ * @rpdev:	rpmsg device we are connected to
+ * @xfer_ack:	completion for host command transfer.
+ * @host_event_work:	Work struct for pending host event.
+ */
+struct cros_ec_rpmsg {
+	struct rpmsg_device *rpdev;
+	struct completion xfer_ack;
+	struct work_struct host_event_work;
+};
+
+/**
+ * cros_ec_cmd_xfer_rpmsg - Transfer a message over rpmsg and receive the reply
+ *
+ * @ec_dev: ChromeOS EC device
+ * @ec_msg: Message to transfer
+ *
+ * This is only used for old EC proto version, and is not supported for this
+ * driver.
+ *
+ * Return: -EINVAL
+ */
+static int cros_ec_cmd_xfer_rpmsg(struct cros_ec_device *ec_dev,
+				  struct cros_ec_command *ec_msg)
+{
+	return -EINVAL;
+}
+
+/**
+ * cros_ec_pkt_xfer_rpmsg - Transfer a packet over rpmsg and receive the reply
+ *
+ * @ec_dev: ChromeOS EC device
+ * @ec_msg: Message to transfer
+ *
+ * Return: number of bytes of the reply on success or negative error code.
+ */
+static int cros_ec_pkt_xfer_rpmsg(struct cros_ec_device *ec_dev,
+				  struct cros_ec_command *ec_msg)
+{
+	struct cros_ec_rpmsg *ec_rpmsg = ec_dev->priv;
+	struct rpmsg_device *rpdev = ec_rpmsg->rpdev;
+	struct ec_host_response *response;
+	unsigned long timeout;
+	int len;
+	int ret;
+	u8 sum;
+	int i;
+
+	ec_msg->result = 0;
+	len = cros_ec_prepare_tx(ec_dev, ec_msg);
+	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
+
+	reinit_completion(&ec_rpmsg->xfer_ack);
+	ret = rpmsg_send(rpdev->ept, ec_dev->dout, len);
+	if (ret) {
+		dev_err(ec_dev->dev, "rpmsg send failed\n");
+		return ret;
+	}
+
+	timeout = msecs_to_jiffies(EC_MSG_TIMEOUT_MS);
+	ret = wait_for_completion_timeout(&ec_rpmsg->xfer_ack, timeout);
+	if (!ret) {
+		dev_err(ec_dev->dev, "rpmsg send timeout\n");
+		return -EIO;
+	}
+
+	/* check response error code */
+	response = (struct ec_host_response *)ec_dev->din;
+	ec_msg->result = response->result;
+
+	ret = cros_ec_check_result(ec_dev, ec_msg);
+	if (ret)
+		goto exit;
+
+	if (response->data_len > ec_msg->insize) {
+		dev_err(ec_dev->dev, "packet too long (%d bytes, expected %d)",
+			response->data_len, ec_msg->insize);
+		ret = -EMSGSIZE;
+		goto exit;
+	}
+
+	/* copy response packet payload and compute checksum */
+	memcpy(ec_msg->data, ec_dev->din + sizeof(*response),
+	       response->data_len);
+
+	sum = 0;
+	for (i = 0; i < sizeof(*response) + response->data_len; i++)
+		sum += ec_dev->din[i];
+
+	if (sum) {
+		dev_err(ec_dev->dev, "bad packet checksum, calculated %x\n",
+			sum);
+		ret = -EBADMSG;
+		goto exit;
+	}
+
+	ret = response->data_len;
+exit:
+	if (ec_msg->command == EC_CMD_REBOOT_EC)
+		msleep(EC_REBOOT_DELAY_MS);
+
+	return ret;
+}
+
+static void
+cros_ec_rpmsg_host_event_function(struct work_struct *host_event_work)
+{
+	struct cros_ec_rpmsg *ec_rpmsg = container_of(host_event_work,
+						      struct cros_ec_rpmsg,
+						      host_event_work);
+	struct cros_ec_device *ec_dev = dev_get_drvdata(&ec_rpmsg->rpdev->dev);
+	bool wake_event = true;
+	int ret;
+
+	ret = cros_ec_get_next_event(ec_dev, &wake_event);
+
+	/*
+	 * Signal only if wake host events or any interrupt if
+	 * cros_ec_get_next_event() returned an error (default value for
+	 * wake_event is true)
+	 */
+	if (wake_event && device_may_wakeup(ec_dev->dev))
+		pm_wakeup_event(ec_dev->dev, 0);
+
+	if (ret > 0)
+		blocking_notifier_call_chain(&ec_dev->event_notifier,
+					     0, ec_dev);
+}
+
+static int cros_ec_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
+				  int len, void *priv, u32 src)
+{
+	struct cros_ec_device *ec_dev = dev_get_drvdata(&rpdev->dev);
+	struct cros_ec_rpmsg *ec_rpmsg = ec_dev->priv;
+	struct cros_ec_rpmsg_response *resp;
+
+	if (!len) {
+		dev_warn(ec_dev->dev, "rpmsg received empty response");
+		return -EINVAL;
+	}
+
+	resp = data;
+	len -= offsetof(struct cros_ec_rpmsg_response, data);
+	if (resp->type == HOST_COMMAND_MARK) {
+		if (len > ec_dev->din_size) {
+			dev_warn(ec_dev->dev,
+				 "received length %d > din_size %d, truncating",
+				 len, ec_dev->din_size);
+			len = ec_dev->din_size;
+		}
+
+		memcpy(ec_dev->din, resp->data, len);
+		complete(&ec_rpmsg->xfer_ack);
+	} else if (resp->type == HOST_EVENT_MARK) {
+		schedule_work(&ec_rpmsg->host_event_work);
+	} else {
+		dev_warn(ec_dev->dev, "rpmsg received invalid type = %d",
+			 resp->type);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int cros_ec_rpmsg_probe(struct rpmsg_device *rpdev)
+{
+	struct device *dev = &rpdev->dev;
+	struct cros_ec_rpmsg *ec_rpmsg;
+	struct cros_ec_device *ec_dev;
+
+	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
+	if (!ec_dev)
+		return -ENOMEM;
+
+	ec_rpmsg = devm_kzalloc(dev, sizeof(*ec_rpmsg), GFP_KERNEL);
+	if (!ec_rpmsg)
+		return -ENOMEM;
+
+	ec_dev->dev = dev;
+	ec_dev->priv = ec_rpmsg;
+	ec_dev->cmd_xfer = cros_ec_cmd_xfer_rpmsg;
+	ec_dev->pkt_xfer = cros_ec_pkt_xfer_rpmsg;
+	ec_dev->phys_name = dev_name(&rpdev->dev);
+	ec_dev->din_size = sizeof(struct ec_host_response) +
+			   sizeof(struct ec_response_get_protocol_info);
+	ec_dev->dout_size = sizeof(struct ec_host_request);
+	dev_set_drvdata(dev, ec_dev);
+
+	ec_rpmsg->rpdev = rpdev;
+	init_completion(&ec_rpmsg->xfer_ack);
+	INIT_WORK(&ec_rpmsg->host_event_work,
+		  cros_ec_rpmsg_host_event_function);
+
+	return cros_ec_register(ec_dev);
+}
+
+static void cros_ec_rpmsg_remove(struct rpmsg_device *rpdev)
+{
+	struct cros_ec_device *ec_dev = dev_get_drvdata(&rpdev->dev);
+	struct cros_ec_rpmsg *ec_rpmsg = ec_dev->priv;
+
+	cancel_work_sync(&ec_rpmsg->host_event_work);
+}
+
+static const struct of_device_id cros_ec_rpmsg_of_match[] = {
+	{ .compatible = "google,cros-ec-rpmsg", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, cros_ec_rpmsg_of_match);
+
+static struct rpmsg_driver cros_ec_driver_rpmsg = {
+	.drv = {
+		.name   = "cros-ec-rpmsg",
+		.of_match_table = cros_ec_rpmsg_of_match,
+	},
+	.probe		= cros_ec_rpmsg_probe,
+	.remove		= cros_ec_rpmsg_remove,
+	.callback	= cros_ec_rpmsg_callback,
+};
+
+module_rpmsg_driver(cros_ec_driver_rpmsg);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("ChromeOS EC multi function device (rpmsg)");