[PATCH v2 2/2] platform/chrome: wilco_ec: Add telemetry char device interface

[Nick Crews]

The Wilco Embedded Controller is able to send telemetry data
which is useful for enterprise applications. A daemon running on
the OS sends a command to the EC via a write() to a char device,
and can read the response with a read(). The write() request is
verified by the driver to ensure that it is performing only one
of the whitelisted commands, and that no extraneous data is
being transmitted to the EC. The response is passed directly
back to the reader with no modification.

The character device will appear as /dev/wilco_telemN, where N
is some small non-negative integer, starting with 0. Only one
process may have the file descriptor open at a time. The calling
userspace program needs to keep the device file descriptor open
between the calls to write() and read() in order to preserve the
response. 32 bytes of data are expected for arguments, and 32
bytes will be available for reading.

For testing purposes, try requesting the EC's firmware build
date, by sending the WILCO_EC_CMD_GET_VERSION command with
argument index=3. i.e. write [0x38, 0x00, 0x03, ...(29 more 0s)]
to the device node. An ASCII string of the build date is
returned.

Signed-off-by: Nick Crews <ncrews@xxxxxxxxxxxx>
---
v2 changes:
- Add verification of userspace requests, so that only
  whitelisted commands and args can get sent to the EC
- Use EC firmware build date request as example/test
- Pass the wilco_ec_device to the child driver better,
  instead of the child driver needing to access the parent
  devices' data.

 drivers/platform/chrome/wilco_ec/Kconfig     |   7 +
 drivers/platform/chrome/wilco_ec/Makefile    |   2 +
 drivers/platform/chrome/wilco_ec/core.c      |  13 +
 drivers/platform/chrome/wilco_ec/debugfs.c   |   2 +-
 drivers/platform/chrome/wilco_ec/telemetry.c | 433 +++++++++++++++++++
 include/linux/platform_data/wilco-ec.h       |   2 +
 6 files changed, 458 insertions(+), 1 deletion(-)
 create mode 100644 drivers/platform/chrome/wilco_ec/telemetry.c

diff --git a/drivers/platform/chrome/wilco_ec/Kconfig b/drivers/platform/chrome/wilco_ec/Kconfig
index e09e4cebe9b4..2fc03aa624cf 100644
--- a/drivers/platform/chrome/wilco_ec/Kconfig
+++ b/drivers/platform/chrome/wilco_ec/Kconfig
@@ -18,3 +18,10 @@ config WILCO_EC_DEBUGFS
 	  manipulation and allow for testing arbitrary commands.  This
 	  interface is intended for debug only and will not be present
 	  on production devices.
+
+config WILCO_EC_TELEMETRY
+	tristate "Enable querying telemetry data from EC"
+	depends on WILCO_EC
+	help
+	  If you say Y here, you get support to query EC telemetry data from
+	  /dev/wilco_telem0 using write() and then read().
diff --git a/drivers/platform/chrome/wilco_ec/Makefile b/drivers/platform/chrome/wilco_ec/Makefile
index 063e7fb4ea17..b4aa6d26a3df 100644
--- a/drivers/platform/chrome/wilco_ec/Makefile
+++ b/drivers/platform/chrome/wilco_ec/Makefile
@@ -4,3 +4,5 @@ wilco_ec-objs				:= core.o mailbox.o
 obj-$(CONFIG_WILCO_EC)			+= wilco_ec.o
 wilco_ec_debugfs-objs			:= debugfs.o
 obj-$(CONFIG_WILCO_EC_DEBUGFS)		+= wilco_ec_debugfs.o
+wilco_ec_telem-objs			:= telemetry.o
+obj-$(CONFIG_WILCO_EC_TELEMETRY)	+= wilco_ec_telem.o
diff --git a/drivers/platform/chrome/wilco_ec/core.c b/drivers/platform/chrome/wilco_ec/core.c
index d060d3aa5bae..4cb05d80e5af 100644
--- a/drivers/platform/chrome/wilco_ec/core.c
+++ b/drivers/platform/chrome/wilco_ec/core.c
@@ -87,8 +87,20 @@ static int wilco_ec_probe(struct platform_device *pdev)
 		goto unregister_debugfs;
 	}
 
+	/* Register child device that will be found by the telemetry driver. */
+	ec->telem_pdev = platform_device_register_data(dev, "wilco_telem",
+						       PLATFORM_DEVID_AUTO,
+						       ec, sizeof(*ec));
+	if (IS_ERR(ec->telem_pdev)) {
+		dev_err(dev, "Failed to create telemetry platform device\n");
+		ret = PTR_ERR(ec->telem_pdev);
+		goto unregister_rtc;
+	}
+
 	return 0;
 
+unregister_rtc:
+	platform_device_unregister(ec->rtc_pdev);
 unregister_debugfs:
 	if (ec->debugfs_pdev)
 		platform_device_unregister(ec->debugfs_pdev);
@@ -100,6 +112,7 @@ static int wilco_ec_remove(struct platform_device *pdev)
 {
 	struct wilco_ec_device *ec = platform_get_drvdata(pdev);
 
+	platform_device_unregister(ec->telem_pdev);
 	platform_device_unregister(ec->rtc_pdev);
 	if (ec->debugfs_pdev)
 		platform_device_unregister(ec->debugfs_pdev);
diff --git a/drivers/platform/chrome/wilco_ec/debugfs.c b/drivers/platform/chrome/wilco_ec/debugfs.c
index 281ec595e8e0..8d65a1e2f1a3 100644
--- a/drivers/platform/chrome/wilco_ec/debugfs.c
+++ b/drivers/platform/chrome/wilco_ec/debugfs.c
@@ -16,7 +16,7 @@
 
 #define DRV_NAME "wilco-ec-debugfs"
 
-/* The 256 raw bytes will take up more space when represented as a hex string */
+/* The raw bytes will take up more space when represented as a hex string */
 #define FORMATTED_BUFFER_SIZE (EC_MAILBOX_DATA_SIZE * 4)
 
 struct wilco_ec_debugfs {
diff --git a/drivers/platform/chrome/wilco_ec/telemetry.c b/drivers/platform/chrome/wilco_ec/telemetry.c
new file mode 100644
index 000000000000..3eed7f44ff09
--- /dev/null
+++ b/drivers/platform/chrome/wilco_ec/telemetry.c
@@ -0,0 +1,433 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Telemetry communication for Wilco EC
+ *
+ * Copyright 2019 Google LLC
+ *
+ * The Wilco Embedded Controller is able to send telemetry data
+ * which is useful for enterprise applications. A daemon running on
+ * the OS sends a command to the EC via a write() to a char device,
+ * and can read the response with a read(). The write() request is
+ * verified by the driver to ensure that it is performing only one
+ * of the whitelisted commands, and that no extraneous data is
+ * being transmitted to the EC. The response is passed directly
+ * back to the reader with no modification.
+ *
+ * The character device will appear as /dev/wilco_telemN, where N
+ * is some small non-negative integer, starting with 0. Only one
+ * process may have the file descriptor open at a time. The calling
+ * userspace program needs to keep the device file descriptor open
+ * between the calls to write() and read() in order to preserve the
+ * response. 32 bytes of data are expected for arguments, and 32
+ * bytes will be available for reading.
+ *
+ * For testing purposes, try requesting the EC's firmware build
+ * date, by sending the WILCO_EC_CMD_GET_VERSION command with
+ * argument index=3. i.e. write [0x38, 0x00, 0x03, ...(29 more 0s)]
+ * to the device node. An ASCII string of the build date is
+ * returned.
+ */
+
+#include <linux/cdev.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/platform_data/wilco-ec.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+
+#define TELEM_DEV_NAME		"wilco_telem"
+#define TELEM_CLASS_NAME	TELEM_DEV_NAME
+#define DRV_NAME		TELEM_DEV_NAME
+#define TELEM_DEV_NAME_FMT	(TELEM_DEV_NAME "%d")
+static struct class telem_class = {
+	.owner	= THIS_MODULE,
+	.name	= TELEM_CLASS_NAME,
+};
+
+/* Keep track of all the device numbers used. */
+#define TELEM_MAX_DEV 128
+static int telem_major;
+static DEFINE_IDA(telem_ida);
+
+/* EC command codes */
+#define WILCO_EC_CMD_GET_LOG		0x99
+#define WILCO_EC_CMD_GET_VERSION	0x38
+#define WILCO_EC_CMD_GET_FAN_INFO	0x2E
+#define WILCO_EC_CMD_GET_DIAG_INFO	0xFA
+#define WILCO_EC_CMD_GET_TEMP_INFO	0x95
+#define WILCO_EC_CMD_GET_TEMP_READ	0x2C
+#define WILCO_EC_CMD_GET_BATT_EXT_INFO	0x07
+
+#define TELEM_ARGS_SIZE_MAX	30
+
+struct wilco_ec_telem_request {
+	u8 command;	/* One of WILCO_EC_CMD_GET_* command codes */
+	u8 reserved;	/* Must be 0 */
+	u8 args[TELEM_ARGS_SIZE_MAX];	/* One of telem_args_get_* structs */
+} __packed;
+
+/*
+ * The following telem_args_get_* structs are embedded within the |args| field
+ * of wilco_ec_telem_request.
+ */
+
+struct telem_args_get_log {
+	u8 log_type;
+	u8 log_index;
+} __packed;
+
+/*
+ * Get a piece of info about the EC firmware version:
+ * 0 = label
+ * 1 = svn_rev
+ * 2 = model_no
+ * 3 = build_date
+ * 4 = frio_version
+ */
+struct telem_args_get_version {
+	u8 index;
+} __packed;
+
+struct telem_args_get_fan_info {
+	u8 command;
+	u8 fan_number;
+	u8 arg;
+} __packed;
+
+struct telem_args_get_diag_info {
+	u8 type;
+} __packed;
+
+struct telem_args_get_temp_info {
+	u8 command;
+	u8 index;
+	u8 field;
+	u8 zone;
+} __packed;
+
+struct telem_args_get_temp_read {
+	u8 sensor_index;
+} __packed;
+
+struct telem_args_get_batt_ext_info {
+	u8 var_args[5];
+} __packed;
+
+static const char TELEM_ARGS_ZERO[TELEM_ARGS_SIZE_MAX] = {0};
+
+/**
+ * check_args_length() - Ensure that un-needed argument bytes are 0.
+ * @rq:	Request to be validated.
+ * @arg_size: Number of bytes of rq->args that are allowed to be non-zero.
+ */
+static int check_args_length(struct wilco_ec_telem_request *rq, size_t arg_size)
+{
+	if (memcmp(rq->args + arg_size, TELEM_ARGS_ZERO,
+		   TELEM_ARGS_SIZE_MAX-arg_size) != 0)
+		return -EINVAL;
+
+	return 0;
+}
+
+/*
+ * We do not want to allow userspace to send arbitrary telemetry commands to
+ * the EC. Therefore we check to ensure that
+ * 1. The request follows the format of struct wilco_ec_telem_request.
+ * 2. The supplied command code is one of the whitelisted commands.
+ * 3. The arguments only contain the necessary data. Each command takes a
+ *    different format of arguments, and only these arguments can be
+ *    non-zero. For instance, if the request uses command WILCO_EC_CMD_GET_LOG,
+ *    then the command uses the argument format of telem_args_get_log, which
+ *    contains 2 bytes of arguments. Thus, everything in the args besides these
+ *    two bytes had better be zero.
+ */
+static int check_telem_request(struct wilco_ec_telem_request *rq)
+{
+	if (rq->reserved)
+		return -EINVAL;
+
+	switch (rq->command) {
+	case WILCO_EC_CMD_GET_LOG:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_log));
+	case WILCO_EC_CMD_GET_VERSION:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_version));
+	case WILCO_EC_CMD_GET_FAN_INFO:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_fan_info));
+	case WILCO_EC_CMD_GET_DIAG_INFO:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_diag_info));
+	case WILCO_EC_CMD_GET_TEMP_INFO:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_temp_info));
+	case WILCO_EC_CMD_GET_TEMP_READ:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_temp_read));
+	case WILCO_EC_CMD_GET_BATT_EXT_INFO:
+		return check_args_length(rq,
+				sizeof(struct telem_args_get_batt_ext_info));
+	default:
+		return -EINVAL;
+	}
+}
+
+/**
+ * struct telem_device_data - Data for a Wilco EC device that queries telemetry.
+ * @cdev: Char dev that userspace reads and polls from.
+ * @dev: Device associated with the %cdev.
+ * @ec: Wilco EC that we will be communicating with using the mailbox interface.
+ * @available: Boolean of if the device can be opened.
+ */
+struct telem_device_data {
+	struct device dev;
+	struct cdev cdev;
+	struct wilco_ec_device *ec;
+	atomic_t available;
+};
+
+#define TELEM_RESPONSE_SIZE	EC_MAILBOX_DATA_SIZE
+
+/**
+ * struct telem_session_data - Data that exists between open() and release().
+ * @dev_data: Pointer to get back to the device data and EC.
+ * @request: Command and arguments sent to EC.
+ * @response: Response buffer of data from EC.
+ * @has_msg: Is there data available to read from a previous write?
+ */
+struct telem_session_data {
+	struct telem_device_data *dev_data;
+	struct wilco_ec_telem_request request;
+	u8 response[TELEM_RESPONSE_SIZE];
+	bool has_msg;
+};
+
+/**
+ * telem_open() - Callback for when the device node is opened.
+ * @inode: inode for this char device node.
+ * @filp: file for this char device node.
+ *
+ * We need to ensure that after writing a command to the device,
+ * the same userspace process reads the corresponding result.
+ * Therefore, we increment a refcount on opening the device, so that
+ * only one process can communicate with the EC at a time.
+ *
+ * Return: 0 on success, or negative error code on failure.
+ */
+static int telem_open(struct inode *inode, struct file *filp)
+{
+	struct telem_device_data *dev_data;
+	struct telem_session_data *sess_data;
+
+	/* Ensure device isn't already open */
+	dev_data = container_of(inode->i_cdev, struct telem_device_data, cdev);
+	if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
+		return -EBUSY;
+
+	sess_data = kzalloc(sizeof(*sess_data), GFP_KERNEL);
+	if (!sess_data) {
+		atomic_set(&dev_data->available, 1);
+		return -ENOMEM;
+	}
+	sess_data->dev_data = dev_data;
+	sess_data->has_msg = false;
+
+	nonseekable_open(inode, filp);
+	filp->private_data = sess_data;
+
+	return 0;
+}
+
+static ssize_t telem_write(struct file *filp, const char __user *buf,
+			   size_t count, loff_t *pos)
+{
+	struct telem_session_data *sess_data = filp->private_data;
+	struct wilco_ec_message msg = {};
+	int ret;
+
+	if (count != sizeof(sess_data->request))
+		return -EINVAL;
+	if (copy_from_user(&sess_data->request, buf, count))
+		return -EFAULT;
+	ret = check_telem_request(&sess_data->request);
+	if (ret < 0)
+		return ret;
+
+	msg.type = WILCO_EC_MSG_TELEMETRY;
+	msg.request_data = &sess_data->request;
+	msg.request_size = sizeof(sess_data->request);
+	msg.response_data = sess_data->response;
+	msg.response_size = sizeof(sess_data->response);
+
+	ret = wilco_ec_mailbox(sess_data->dev_data->ec, &msg);
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(sess_data->response))
+		return -EMSGSIZE;
+
+	sess_data->has_msg = true;
+
+	return count;
+}
+
+static ssize_t telem_read(struct file *filp, char __user *buf, size_t count,
+			  loff_t *pos)
+{
+	struct telem_session_data *sess_data = filp->private_data;
+
+	if (!sess_data->has_msg)
+		return -ENODATA;
+	if (count > sizeof(sess_data->response))
+		return -EINVAL;
+
+	if (copy_to_user(buf, sess_data->response, count))
+		return -EFAULT;
+
+	sess_data->has_msg = false;
+
+	return count;
+}
+
+static int telem_release(struct inode *inode, struct file *filp)
+{
+	struct telem_session_data *sess_data = filp->private_data;
+
+	atomic_set(&sess_data->dev_data->available, 1);
+	kfree(sess_data);
+
+	return 0;
+}
+
+static const struct file_operations telem_fops = {
+	.open = telem_open,
+	.write = telem_write,
+	.read = telem_read,
+	.release = telem_release,
+	.llseek = no_llseek,
+	.owner = THIS_MODULE,
+};
+
+/**
+ * telem_device_probe() - Callback when creating a new device.
+ * @pdev: platform device that we will be receiving telems from.
+ *
+ * This finds a free minor number for the device, allocates and initializes
+ * some device data, and creates a new device and char dev node.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+static int telem_device_probe(struct platform_device *pdev)
+{
+	struct telem_device_data *dev_data;
+	dev_t dev_num;
+	int error, minor;
+
+	/* Get the next available device number */
+	minor = ida_alloc_max(&telem_ida, TELEM_MAX_DEV-1, GFP_KERNEL);
+	if (minor < 0) {
+		error = minor;
+		dev_err(&pdev->dev, "Failed to find minor number: %d", error);
+		return error;
+	}
+
+	dev_data = devm_kzalloc(&pdev->dev, sizeof(*dev_data), GFP_KERNEL);
+	if (!dev_data) {
+		ida_simple_remove(&telem_ida, minor);
+		return -ENOMEM;
+	}
+
+	/* Initialize the device data */
+	dev_data->ec = dev_get_platdata(&pdev->dev);
+	atomic_set(&dev_data->available, 1);
+	platform_set_drvdata(pdev, dev_data);
+
+	/* Initialize the device */
+	dev_num = MKDEV(telem_major, minor);
+	dev_data->dev.devt = dev_num;
+	dev_data->dev.class = &telem_class;
+	dev_set_name(&dev_data->dev, TELEM_DEV_NAME_FMT, minor);
+	device_initialize(&dev_data->dev);
+
+	/* Initialize the character device and add it to userspace */;
+	cdev_init(&dev_data->cdev, &telem_fops);
+	error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
+	if (error) {
+		ida_simple_remove(&telem_ida, minor);
+		return error;
+	}
+
+	return 0;
+}
+
+static int telem_device_remove(struct platform_device *pdev)
+{
+	struct telem_device_data *dev_data = platform_get_drvdata(pdev);
+
+	cdev_device_del(&dev_data->cdev, &dev_data->dev);
+	ida_simple_remove(&telem_ida, MINOR(dev_data->dev.devt));
+
+	return 0;
+}
+
+static struct platform_driver telem_driver = {
+	.probe = telem_device_probe,
+	.remove = telem_device_remove,
+	.driver = {
+		.name = DRV_NAME,
+	},
+};
+
+static int __init telem_module_init(void)
+{
+	dev_t dev_num = 0;
+	int ret;
+
+	ret = class_register(&telem_class);
+	if (ret) {
+		pr_warn(DRV_NAME ": Failed registering class: %d", ret);
+		return ret;
+	}
+
+	/* Request the kernel for device numbers, starting with minor=0 */
+	ret = alloc_chrdev_region(&dev_num, 0, TELEM_MAX_DEV, TELEM_DEV_NAME);
+	if (ret) {
+		pr_warn(DRV_NAME ": Failed allocating dev numbers: %d", ret);
+		goto destroy_class;
+	}
+	telem_major = MAJOR(dev_num);
+
+	ret = platform_driver_register(&telem_driver);
+	if (ret < 0) {
+		pr_warn(DRV_NAME ": Failed registering driver: %d\n", ret);
+		goto unregister_region;
+	}
+
+	return 0;
+
+unregister_region:
+	unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
+destroy_class:
+	class_unregister(&telem_class);
+	ida_destroy(&telem_ida);
+	return ret;
+}
+
+static void __exit telem_module_exit(void)
+{
+	platform_driver_unregister(&telem_driver);
+	unregister_chrdev_region(MKDEV(telem_major, 0), TELEM_MAX_DEV);
+	class_unregister(&telem_class);
+	ida_destroy(&telem_ida);
+}
+
+module_init(telem_module_init);
+module_exit(telem_module_exit);
+
+MODULE_AUTHOR("Nick Crews <ncrews@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Wilco EC telemetry driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:" DRV_NAME);
diff --git a/include/linux/platform_data/wilco-ec.h b/include/linux/platform_data/wilco-ec.h
index e8e1c6e52d83..1a5aeceb6270 100644
--- a/include/linux/platform_data/wilco-ec.h
+++ b/include/linux/platform_data/wilco-ec.h
@@ -29,6 +29,7 @@
  * @data_size: Size of the data buffer used for EC communication.
  * @debugfs_pdev: The child platform_device used by the debugfs sub-driver.
  * @rtc_pdev: The child platform_device used by the RTC sub-driver.
+ * @telem_pdev: The child platform_device used by the telemetry sub-driver.
  */
 struct wilco_ec_device {
 	struct device *dev;
@@ -40,6 +41,7 @@ struct wilco_ec_device {
 	size_t data_size;
 	struct platform_device *debugfs_pdev;
 	struct platform_device *rtc_pdev;
+	struct platform_device *telem_pdev;
 };
 
 /**
-- 
2.20.1