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Subject[PATCH v5] platform/chrome: wilco_ec: Add telemetry char device interface
Date
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. Up to 32 bytes will be available for reading.

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

Signed-off-by: Nick Crews <ncrews@chromium.org>
---
v5 changes:
- Free device data in callback so that it isn't freed while
the character device is open.
- Remove under-used dev_num variable in probe()
- Change pr_warn to pr_err in module_init()
- Allow for telemetry requests smaller than 32 bytes,
and improve the validation on the requests.
- Return -EMSGSIZE instead of -EINVAL in for too-long requests.
- Zero out response buffer before making a request, so the
response is more clearly padded.
v3 changes:
- Change WILCO_EC_CMD_* commands to WILCO_EC_TELEM_* in
order to differentiate from the 0xF0 commannds.
- Use kernel-doc style for wilco_ec_telem_request.
- Change "GPL v2" to "GPL" in MODULE_LICENSE.
- Fix formatting in check_args_length().
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 | 450 +++++++++++++++++++
include/linux/platform_data/wilco-ec.h | 2 +
6 files changed, 475 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 72df9b5e1983..72a99f854241 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 properties.o sysfs.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 45cf3a5ed062..3724bf4b77c6 100644
--- a/drivers/platform/chrome/wilco_ec/core.c
+++ b/drivers/platform/chrome/wilco_ec/core.c
@@ -93,8 +93,20 @@ static int wilco_ec_probe(struct platform_device *pdev)
goto unregister_rtc;
}

+ /* 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 remove_sysfs;
+ }
+
return 0;

+remove_sysfs:
+ wilco_ec_remove_sysfs(ec);
unregister_rtc:
platform_device_unregister(ec->rtc_pdev);
unregister_debugfs:
@@ -109,6 +121,7 @@ static int wilco_ec_remove(struct platform_device *pdev)
struct wilco_ec_device *ec = platform_get_drvdata(pdev);

wilco_ec_remove_sysfs(ec);
+ 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..94cdc166c840
--- /dev/null
+++ b/drivers/platform/chrome/wilco_ec/telemetry.c
@@ -0,0 +1,450 @@
+// 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. Up to 32 bytes will be available for reading.
+ *
+ * For testing purposes, try requesting the EC's firmware build
+ * date, by sending the WILCO_EC_TELEM_GET_VERSION command with
+ * argument index=3. i.e. write [0x38, 0x00, 0x03]
+ * 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 telemetry command codes */
+#define WILCO_EC_TELEM_GET_LOG 0x99
+#define WILCO_EC_TELEM_GET_VERSION 0x38
+#define WILCO_EC_TELEM_GET_FAN_INFO 0x2E
+#define WILCO_EC_TELEM_GET_DIAG_INFO 0xFA
+#define WILCO_EC_TELEM_GET_TEMP_INFO 0x95
+#define WILCO_EC_TELEM_GET_TEMP_READ 0x2C
+#define WILCO_EC_TELEM_GET_BATT_EXT_INFO 0x07
+
+#define TELEM_ARGS_SIZE_MAX 30
+
+/**
+ * struct wilco_ec_telem_request - Telemetry command and arguments sent to EC.
+ * @command: One of WILCO_EC_TELEM_GET_* command codes.
+ * @reserved: Must be 0.
+ * @args: The first N bytes are one of telem_args_get_* structs, the rest is 0.
+ */
+struct wilco_ec_telem_request {
+ u8 command;
+ u8 reserved;
+ u8 args[TELEM_ARGS_SIZE_MAX];
+} __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;
+ u8 sub_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;
+
+/**
+ * check_telem_request() - Ensure that a request from userspace is valid.
+ * @rq: Request buffer copied from userspace.
+ * @size: Number of bytes copied from userspace.
+ *
+ * Return: 0 if valid, -EINVAL if bad command or reserved byte is non-zero,
+ * -EMSGSIZE if the request is too long.
+ *
+ * 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 request only contains the necessary data for the header and arguments.
+ */
+static int check_telem_request(struct wilco_ec_telem_request *rq,
+ size_t size)
+{
+ size_t max_size = offsetof(struct wilco_ec_telem_request, args);
+
+ if (rq->reserved)
+ return -EINVAL;
+
+ switch (rq->command) {
+ case WILCO_EC_TELEM_GET_LOG:
+ max_size += sizeof(struct telem_args_get_log);
+ break;
+ case WILCO_EC_TELEM_GET_VERSION:
+ max_size += sizeof(struct telem_args_get_version);
+ break;
+ case WILCO_EC_TELEM_GET_FAN_INFO:
+ max_size += sizeof(struct telem_args_get_fan_info);
+ break;
+ case WILCO_EC_TELEM_GET_DIAG_INFO:
+ max_size += sizeof(struct telem_args_get_diag_info);
+ break;
+ case WILCO_EC_TELEM_GET_TEMP_INFO:
+ max_size += sizeof(struct telem_args_get_temp_info);
+ break;
+ case WILCO_EC_TELEM_GET_TEMP_READ:
+ max_size += sizeof(struct telem_args_get_temp_read);
+ break;
+ case WILCO_EC_TELEM_GET_BATT_EXT_INFO:
+ max_size += sizeof(struct telem_args_get_batt_ext_info);
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return (size <= max_size) ? 0 : -EMSGSIZE;
+}
+
+/**
+ * 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;
+
+ get_device(&dev_data->dev);
+
+ 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 -EMSGSIZE;
+ if (copy_from_user(&sess_data->request, buf, count))
+ return -EFAULT;
+ ret = check_telem_request(&sess_data->request, count);
+ if (ret < 0)
+ return ret;
+
+ memset(sess_data->response, 0, sizeof(sess_data->response));
+ 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);
+ put_device(&sess_data->dev_data->dev);
+ 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_free() - Callback to free the telem_device_data structure.
+ * @d: The device embedded in our device data, which we have been ref counting.
+ *
+ * Once all open file descriptors are closed and the device has been removed,
+ * the refcount of the device will fall to 0 and this will be called.
+ */
+static void telem_device_free(struct device *d)
+{
+ struct telem_device_data *dev_data;
+
+ dev_data = container_of(d, struct telem_device_data, dev);
+ kfree(dev_data);
+}
+
+/**
+ * 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;
+ 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 = kzalloc(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_data->dev.devt = MKDEV(telem_major, minor);
+ dev_data->dev.class = &telem_class;
+ dev_data->dev.release = telem_device_free;
+ 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) {
+ put_device(&dev_data->dev);
+ 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);
+ put_device(&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_err(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_err(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_err(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@chromium.org>");
+MODULE_DESCRIPTION("Wilco EC telemetry driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:" DRV_NAME);
diff --git a/include/linux/platform_data/wilco-ec.h b/include/linux/platform_data/wilco-ec.h
index e3ce9ce49b11..ad03b586a095 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
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