// 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 allowlisted 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/mod_devicetable.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 … #define TELEM_CLASS_NAME … #define DRV_NAME … #define TELEM_DEV_NAME_FMT … static struct class telem_class = …; /* Keep track of all the device numbers used. */ #define TELEM_MAX_DEV … static int telem_major; static DEFINE_IDA(telem_ida); /* EC telemetry command codes */ #define WILCO_EC_TELEM_GET_LOG … #define WILCO_EC_TELEM_GET_VERSION … #define WILCO_EC_TELEM_GET_FAN_INFO … #define WILCO_EC_TELEM_GET_DIAG_INFO … #define WILCO_EC_TELEM_GET_TEMP_INFO … #define WILCO_EC_TELEM_GET_TEMP_READ … #define WILCO_EC_TELEM_GET_BATT_EXT_INFO … #define WILCO_EC_TELEM_GET_BATT_PPID_INFO … #define TELEM_ARGS_SIZE_MAX … /* * The following telem_args_get_* structs are embedded within the |args| field * of wilco_ec_telem_request. */ struct telem_args_get_log { … } __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 { … } __packed; struct telem_args_get_fan_info { … } __packed; struct telem_args_get_diag_info { … } __packed; struct telem_args_get_temp_info { … } __packed; struct telem_args_get_temp_read { … } __packed; struct telem_args_get_batt_ext_info { … } __packed; struct telem_args_get_batt_ppid_info { … } __packed; /** * 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 { … } __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 allowlisted 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) { … } /** * 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 { … }; #define TELEM_RESPONSE_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 { … }; /** * 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) { … } static ssize_t telem_write(struct file *filp, const char __user *buf, size_t count, loff_t *pos) { … } static ssize_t telem_read(struct file *filp, char __user *buf, size_t count, loff_t *pos) { … } static int telem_release(struct inode *inode, struct file *filp) { … } static const struct file_operations telem_fops = …; /** * 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) { … } /** * 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) { … } static void telem_device_remove(struct platform_device *pdev) { … } static const struct platform_device_id telem_id[] = …; MODULE_DEVICE_TABLE(platform, telem_id); static struct platform_driver telem_driver = …; static int __init telem_module_init(void) { … } static void __exit telem_module_exit(void) { … } module_init(…) …; module_exit(telem_module_exit); MODULE_AUTHOR(…) …; MODULE_DESCRIPTION(…) …; MODULE_LICENSE(…) …;
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