/*
 * ACPI AML interfacing support
 *
 * Copyright (C) 2015, Intel Corporation
 * Authors: Lv Zheng <lv.zheng@intel.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

/* #define DEBUG */
#define pr_fmt(fmt) "ACPI: AML: " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/proc_fs.h>
#include <linux/debugfs.h>
#include <linux/circ_buf.h>
#include <linux/acpi.h>
#include "internal.h"

#define ACPI_AML_BUF_ALIGN      (sizeof (acpi_size))
#define ACPI_AML_BUF_SIZE       PAGE_SIZE

#define circ_count(circ) \
        (CIRC_CNT((circ)->head, (circ)->tail, ACPI_AML_BUF_SIZE))
#define circ_count_to_end(circ) \
        (CIRC_CNT_TO_END((circ)->head, (circ)->tail, ACPI_AML_BUF_SIZE))
#define circ_space(circ) \
        (CIRC_SPACE((circ)->head, (circ)->tail, ACPI_AML_BUF_SIZE))
#define circ_space_to_end(circ) \
        (CIRC_SPACE_TO_END((circ)->head, (circ)->tail, ACPI_AML_BUF_SIZE))

#define ACPI_AML_OPENED         0x0001
#define ACPI_AML_CLOSED         0x0002
#define ACPI_AML_IN_USER        0x0004 /* user space is writing cmd */
#define ACPI_AML_IN_KERN        0x0008 /* kernel space is reading cmd */
#define ACPI_AML_OUT_USER       0x0010 /* user space is reading log */
#define ACPI_AML_OUT_KERN       0x0020 /* kernel space is writing log */
#define ACPI_AML_USER           (ACPI_AML_IN_USER | ACPI_AML_OUT_USER)
#define ACPI_AML_KERN           (ACPI_AML_IN_KERN | ACPI_AML_OUT_KERN)
#define ACPI_AML_BUSY           (ACPI_AML_USER | ACPI_AML_KERN)
#define ACPI_AML_OPEN           (ACPI_AML_OPENED | ACPI_AML_CLOSED)

struct acpi_aml_io {
        wait_queue_head_t wait;
        unsigned long flags;
        unsigned long users;
        struct mutex lock;
        struct task_struct *thread;
        char out_buf[ACPI_AML_BUF_SIZE] __aligned(ACPI_AML_BUF_ALIGN);
        struct circ_buf out_crc;
        char in_buf[ACPI_AML_BUF_SIZE] __aligned(ACPI_AML_BUF_ALIGN);
        struct circ_buf in_crc;
        acpi_osd_exec_callback function;
        void *context;
        unsigned long usages;
};

static struct acpi_aml_io acpi_aml_io;
static bool acpi_aml_initialized;
static struct file *acpi_aml_active_reader;
static struct dentry *acpi_aml_dentry;

static inline bool __acpi_aml_running(void)
{
        return acpi_aml_io.thread ? true : false;
}

static inline bool __acpi_aml_access_ok(unsigned long flag)
{
        /*
         * The debugger interface is in opened state (OPENED && !CLOSED),
         * then it is allowed to access the debugger buffers from either
         * user space or the kernel space.
         * In addition, for the kernel space, only the debugger thread
         * (thread ID matched) is allowed to access.
         */
        if (!(acpi_aml_io.flags & ACPI_AML_OPENED) ||
            (acpi_aml_io.flags & ACPI_AML_CLOSED) ||
            !__acpi_aml_running())
                return false;
        if ((flag & ACPI_AML_KERN) &&
            current != acpi_aml_io.thread)
                return false;
        return true;
}

static inline bool __acpi_aml_readable(struct circ_buf *circ, unsigned long flag)
{
        /*
         * Another read is not in progress and there is data in buffer
         * available for read.
         */
        if (!(acpi_aml_io.flags & flag) && circ_count(circ))
                return true;
        return false;
}

static inline bool __acpi_aml_writable(struct circ_buf *circ, unsigned long flag)
{
        /*
         * Another write is not in progress and there is buffer space
         * available for write.
         */
        if (!(acpi_aml_io.flags & flag) && circ_space(circ))
                return true;
        return false;
}

static inline bool __acpi_aml_busy(void)
{
        if (acpi_aml_io.flags & ACPI_AML_BUSY)
                return true;
        return false;
}

static inline bool __acpi_aml_opened(void)
{
        if (acpi_aml_io.flags & ACPI_AML_OPEN)
                return true;
        return false;
}

static inline bool __acpi_aml_used(void)
{
        return acpi_aml_io.usages ? true : false;
}

static inline bool acpi_aml_running(void)
{
        bool ret;

        mutex_lock(&acpi_aml_io.lock);
        ret = __acpi_aml_running();
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static bool acpi_aml_busy(void)
{
        bool ret;

        mutex_lock(&acpi_aml_io.lock);
        ret = __acpi_aml_busy();
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static bool acpi_aml_used(void)
{
        bool ret;

        /*
         * The usage count is prepared to avoid race conditions between the
         * starts and the stops of the debugger thread.
         */
        mutex_lock(&acpi_aml_io.lock);
        ret = __acpi_aml_used();
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static bool acpi_aml_kern_readable(void)
{
        bool ret;

        mutex_lock(&acpi_aml_io.lock);
        ret = !__acpi_aml_access_ok(ACPI_AML_IN_KERN) ||
              __acpi_aml_readable(&acpi_aml_io.in_crc, ACPI_AML_IN_KERN);
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static bool acpi_aml_kern_writable(void)
{
        bool ret;

        mutex_lock(&acpi_aml_io.lock);
        ret = !__acpi_aml_access_ok(ACPI_AML_OUT_KERN) ||
              __acpi_aml_writable(&acpi_aml_io.out_crc, ACPI_AML_OUT_KERN);
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static bool acpi_aml_user_readable(void)
{
        bool ret;

        mutex_lock(&acpi_aml_io.lock);
        ret = !__acpi_aml_access_ok(ACPI_AML_OUT_USER) ||
              __acpi_aml_readable(&acpi_aml_io.out_crc, ACPI_AML_OUT_USER);
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static bool acpi_aml_user_writable(void)
{
        bool ret;

        mutex_lock(&acpi_aml_io.lock);
        ret = !__acpi_aml_access_ok(ACPI_AML_IN_USER) ||
              __acpi_aml_writable(&acpi_aml_io.in_crc, ACPI_AML_IN_USER);
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static int acpi_aml_lock_write(struct circ_buf *circ, unsigned long flag)
{
        int ret = 0;

        mutex_lock(&acpi_aml_io.lock);
        if (!__acpi_aml_access_ok(flag)) {
                ret = -EFAULT;
                goto out;
        }
        if (!__acpi_aml_writable(circ, flag)) {
                ret = -EAGAIN;
                goto out;
        }
        acpi_aml_io.flags |= flag;
out:
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static int acpi_aml_lock_read(struct circ_buf *circ, unsigned long flag)
{
        int ret = 0;

        mutex_lock(&acpi_aml_io.lock);
        if (!__acpi_aml_access_ok(flag)) {
                ret = -EFAULT;
                goto out;
        }
        if (!__acpi_aml_readable(circ, flag)) {
                ret = -EAGAIN;
                goto out;
        }
        acpi_aml_io.flags |= flag;
out:
        mutex_unlock(&acpi_aml_io.lock);
        return ret;
}

static void acpi_aml_unlock_fifo(unsigned long flag, bool wakeup)
{
        mutex_lock(&acpi_aml_io.lock);
        acpi_aml_io.flags &= ~flag;
        if (wakeup)
                wake_up_interruptible(&acpi_aml_io.wait);
        mutex_unlock(&acpi_aml_io.lock);
}

static int acpi_aml_write_kern(const char *buf, int len)
{
        int ret;
        struct circ_buf *crc = &acpi_aml_io.out_crc;
        int n;
        char *p;

        ret = acpi_aml_lock_write(crc, ACPI_AML_OUT_KERN);
        if (ret < 0)
                return ret;
        /* sync tail before inserting logs */
        smp_mb();
        p = &crc->buf[crc->head];
        n = min(len, circ_space_to_end(crc));
        memcpy(p, buf, n);
        /* sync head after inserting logs */
        smp_wmb();
        crc->head = (crc->head + n) & (ACPI_AML_BUF_SIZE - 1);
        acpi_aml_unlock_fifo(ACPI_AML_OUT_KERN, true);
        return n;
}

static int acpi_aml_readb_kern(void)
{
        int ret;
        struct circ_buf *crc = &acpi_aml_io.in_crc;
        char *p;

        ret = acpi_aml_lock_read(crc, ACPI_AML_IN_KERN);
        if (ret < 0)
                return ret;
        /* sync head before removing cmds */
        smp_rmb();
        p = &crc->buf[crc->tail];
        ret = (int)*p;
        /* sync tail before inserting cmds */
        smp_mb();
        crc->tail = (crc->tail + 1) & (ACPI_AML_BUF_SIZE - 1);
        acpi_aml_unlock_fifo(ACPI_AML_IN_KERN, true);
        return ret;
}

/*
 * acpi_aml_write_log() - Capture debugger output
 * @msg: the debugger output
 *
 * This function should be used to implement acpi_os_printf() to filter out
 * the debugger output and store the output into the debugger interface
 * buffer. Return the size of stored logs or errno.
 */
static ssize_t acpi_aml_write_log(const char *msg)
{
        int ret = 0;
        int count = 0, size = 0;

        if (!acpi_aml_initialized)
                return -ENODEV;
        if (msg)
                count = strlen(msg);
        while (count > 0) {
again:
                ret = acpi_aml_write_kern(msg + size, count);
                if (ret == -EAGAIN) {
                        ret = wait_event_interruptible(acpi_aml_io.wait,
                                acpi_aml_kern_writable());
                        /*
                         * We need to retry when the condition
                         * becomes true.
                         */
                        if (ret == 0)
                                goto again;
                        break;
                }
                if (ret < 0)
                        break;
                size += ret;
                count -= ret;
        }
        return size > 0 ? size : ret;
}

/*
 * acpi_aml_read_cmd() - Capture debugger input
 * @msg: the debugger input
 * @size: the size of the debugger input
 *
 * This function should be used to implement acpi_os_get_line() to capture
 * the debugger input commands and store the input commands into the
 * debugger interface buffer. Return the size of stored commands or errno.
 */
static ssize_t acpi_aml_read_cmd(char *msg, size_t count)
{
        int ret = 0;
        int size = 0;

        /*
         * This is ensured by the running fact of the debugger thread
         * unless a bug is introduced.
         */
        BUG_ON(!acpi_aml_initialized);
        while (count > 0) {
again:
                /*
                 * Check each input byte to find the end of the command.
                 */
                ret = acpi_aml_readb_kern();
                if (ret == -EAGAIN) {
                        ret = wait_event_interruptible(acpi_aml_io.wait,
                                acpi_aml_kern_readable());
                        /*
                         * We need to retry when the condition becomes
                         * true.
                         */
                        if (ret == 0)
                                goto again;
                }
                if (ret < 0)
                        break;
                *(msg + size) = (char)ret;
                size++;
                count--;
                if (ret == '\n') {
                        /*
                         * acpi_os_get_line() requires a zero terminated command
                         * string.
                         */
                        *(msg + size - 1) = '\0';
                        break;
                }
        }
        return size > 0 ? size : ret;
}

static int acpi_aml_thread(void *unsed)
{
        acpi_osd_exec_callback function = NULL;
        void *context;

        mutex_lock(&acpi_aml_io.lock);
        if (acpi_aml_io.function) {
                acpi_aml_io.usages++;
                function = acpi_aml_io.function;
                context = acpi_aml_io.context;
        }
        mutex_unlock(&acpi_aml_io.lock);

        if (function)
                function(context);

        mutex_lock(&acpi_aml_io.lock);
        acpi_aml_io.usages--;
        if (!__acpi_aml_used()) {
                acpi_aml_io.thread = NULL;
                wake_up(&acpi_aml_io.wait);
        }
        mutex_unlock(&acpi_aml_io.lock);

        return 0;
}

/*
 * acpi_aml_create_thread() - Create AML debugger thread
 * @function: the debugger thread callback
 * @context: the context to be passed to the debugger thread
 *
 * This function should be used to implement acpi_os_execute() which is
 * used by the ACPICA debugger to create the debugger thread.
 */
static int acpi_aml_create_thread(acpi_osd_exec_callback function, void *context)
{
        struct task_struct *t;

        mutex_lock(&acpi_aml_io.lock);
        acpi_aml_io.function = function;
        acpi_aml_io.context = context;
        mutex_unlock(&acpi_aml_io.lock);

        t = kthread_create(acpi_aml_thread, NULL, "aml");
        if (IS_ERR(t)) {
                pr_err("Failed to create AML debugger thread.\n");
                return PTR_ERR(t);
        }

        mutex_lock(&acpi_aml_io.lock);
        acpi_aml_io.thread = t;
        acpi_set_debugger_thread_id((acpi_thread_id)(unsigned long)t);
        wake_up_process(t);
        mutex_unlock(&acpi_aml_io.lock);
        return 0;
}

static int acpi_aml_wait_command_ready(bool single_step,
                                       char *buffer, size_t length)
{
        acpi_status status;

        if (single_step)
                acpi_os_printf("\n%1c ", ACPI_DEBUGGER_EXECUTE_PROMPT);
        else
                acpi_os_printf("\n%1c ", ACPI_DEBUGGER_COMMAND_PROMPT);

        status = acpi_os_get_line(buffer, length, NULL);
        if (ACPI_FAILURE(status))
                return -EINVAL;
        return 0;
}

static int acpi_aml_notify_command_complete(void)
{
        return 0;
}

static int acpi_aml_open(struct inode *inode, struct file *file)
{
        int ret = 0;
        acpi_status status;

        mutex_lock(&acpi_aml_io.lock);
        /*
         * The debugger interface is being closed, no new user is allowed
         * during this period.
         */
        if (acpi_aml_io.flags & ACPI_AML_CLOSED) {
                ret = -EBUSY;
                goto err_lock;
        }
        if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
                /*
                 * Only one reader is allowed to initiate the debugger
                 * thread.
                 */
                if (acpi_aml_active_reader) {
                        ret = -EBUSY;
                        goto err_lock;
                } else {
                        pr_debug("Opening debugger reader.\n");
                        acpi_aml_active_reader = file;
                }
        } else {
                /*
                 * No writer is allowed unless the debugger thread is
                 * ready.
                 */
                if (!(acpi_aml_io.flags & ACPI_AML_OPENED)) {
                        ret = -ENODEV;
                        goto err_lock;
                }
        }
        if (acpi_aml_active_reader == file) {
                pr_debug("Opening debugger interface.\n");
                mutex_unlock(&acpi_aml_io.lock);

                pr_debug("Initializing debugger thread.\n");
                status = acpi_initialize_debugger();
                if (ACPI_FAILURE(status)) {
                        pr_err("Failed to initialize debugger.\n");
                        ret = -EINVAL;
                        goto err_exit;
                }
                pr_debug("Debugger thread initialized.\n");

                mutex_lock(&acpi_aml_io.lock);
                acpi_aml_io.flags |= ACPI_AML_OPENED;
                acpi_aml_io.out_crc.head = acpi_aml_io.out_crc.tail = 0;
                acpi_aml_io.in_crc.head = acpi_aml_io.in_crc.tail = 0;
                pr_debug("Debugger interface opened.\n");
        }
        acpi_aml_io.users++;
err_lock:
        if (ret < 0) {
                if (acpi_aml_active_reader == file)
                        acpi_aml_active_reader = NULL;
        }
        mutex_unlock(&acpi_aml_io.lock);
err_exit:
        return ret;
}

static int acpi_aml_release(struct inode *inode, struct file *file)
{
        mutex_lock(&acpi_aml_io.lock);
        acpi_aml_io.users--;
        if (file == acpi_aml_active_reader) {
                pr_debug("Closing debugger reader.\n");
                acpi_aml_active_reader = NULL;

                pr_debug("Closing debugger interface.\n");
                acpi_aml_io.flags |= ACPI_AML_CLOSED;

                /*
                 * Wake up all user space/kernel space blocked
                 * readers/writers.
                 */
                wake_up_interruptible(&acpi_aml_io.wait);
                mutex_unlock(&acpi_aml_io.lock);
                /*
                 * Wait all user space/kernel space readers/writers to
                 * stop so that ACPICA command loop of the debugger thread
                 * should fail all its command line reads after this point.
                 */
                wait_event(acpi_aml_io.wait, !acpi_aml_busy());

                /*
                 * Then we try to terminate the debugger thread if it is
                 * not terminated.
                 */
                pr_debug("Terminating debugger thread.\n");
                acpi_terminate_debugger();
                wait_event(acpi_aml_io.wait, !acpi_aml_used());
                pr_debug("Debugger thread terminated.\n");

                mutex_lock(&acpi_aml_io.lock);
                acpi_aml_io.flags &= ~ACPI_AML_OPENED;
        }
        if (acpi_aml_io.users == 0) {
                pr_debug("Debugger interface closed.\n");
                acpi_aml_io.flags &= ~ACPI_AML_CLOSED;
        }
        mutex_unlock(&acpi_aml_io.lock);
        return 0;
}

static int acpi_aml_read_user(char __user *buf, int len)
{
        int ret;
        struct circ_buf *crc = &acpi_aml_io.out_crc;
        int n;
        char *p;

        ret = acpi_aml_lock_read(crc, ACPI_AML_OUT_USER);
        if (ret < 0)
                return ret;
        /* sync head before removing logs */
        smp_rmb();
        p = &crc->buf[crc->tail];
        n = min(len, circ_count_to_end(crc));
        if (copy_to_user(buf, p, n)) {
                ret = -EFAULT;
                goto out;
        }
        /* sync tail after removing logs */
        smp_mb();
        crc->tail = (crc->tail + n) & (ACPI_AML_BUF_SIZE - 1);
        ret = n;
out:
        acpi_aml_unlock_fifo(ACPI_AML_OUT_USER, ret >= 0);
        return ret;
}

static ssize_t acpi_aml_read(struct file *file, char __user *buf,
                             size_t count, loff_t *ppos)
{
        int ret = 0;
        int size = 0;

        if (!count)
                return 0;
        if (!access_ok(buf, count))
                return -EFAULT;

        while (count > 0) {
again:
                ret = acpi_aml_read_user(buf + size, count);
                if (ret == -EAGAIN) {
                        if (file->f_flags & O_NONBLOCK)
                                break;
                        else {
                                ret = wait_event_interruptible(acpi_aml_io.wait,
                                        acpi_aml_user_readable());
                                /*
                                 * We need to retry when the condition
                                 * becomes true.
                                 */
                                if (ret == 0)
                                        goto again;
                        }
                }
                if (ret < 0) {
                        if (!acpi_aml_running())
                                ret = 0;
                        break;
                }
                if (ret) {
                        size += ret;
                        count -= ret;
                        *ppos += ret;
                        break;
                }
        }
        return size > 0 ? size : ret;
}

static int acpi_aml_write_user(const char __user *buf, int len)
{
        int ret;
        struct circ_buf *crc = &acpi_aml_io.in_crc;
        int n;
        char *p;

        ret = acpi_aml_lock_write(crc, ACPI_AML_IN_USER);
        if (ret < 0)
                return ret;
        /* sync tail before inserting cmds */
        smp_mb();
        p = &crc->buf[crc->head];
        n = min(len, circ_space_to_end(crc));
        if (copy_from_user(p, buf, n)) {
                ret = -EFAULT;
                goto out;
        }
        /* sync head after inserting cmds */
        smp_wmb();
        crc->head = (crc->head + n) & (ACPI_AML_BUF_SIZE - 1);
        ret = n;
out:
        acpi_aml_unlock_fifo(ACPI_AML_IN_USER, ret >= 0);
        return n;
}

static ssize_t acpi_aml_write(struct file *file, const char __user *buf,
                              size_t count, loff_t *ppos)
{
        int ret = 0;
        int size = 0;

        if (!count)
                return 0;
        if (!access_ok(buf, count))
                return -EFAULT;

        while (count > 0) {
again:
                ret = acpi_aml_write_user(buf + size, count);
                if (ret == -EAGAIN) {
                        if (file->f_flags & O_NONBLOCK)
                                break;
                        else {
                                ret = wait_event_interruptible(acpi_aml_io.wait,
                                        acpi_aml_user_writable());
                                /*
                                 * We need to retry when the condition
                                 * becomes true.
                                 */
                                if (ret == 0)
                                        goto again;
                        }
                }
                if (ret < 0) {
                        if (!acpi_aml_running())
                                ret = 0;
                        break;
                }
                if (ret) {
                        size += ret;
                        count -= ret;
                        *ppos += ret;
                }
        }
        return size > 0 ? size : ret;
}

static __poll_t acpi_aml_poll(struct file *file, poll_table *wait)
{
        __poll_t masks = 0;

        poll_wait(file, &acpi_aml_io.wait, wait);
        if (acpi_aml_user_readable())
                masks |= EPOLLIN | EPOLLRDNORM;
        if (acpi_aml_user_writable())
                masks |= EPOLLOUT | EPOLLWRNORM;

        return masks;
}

static const struct file_operations acpi_aml_operations = {
        .read           = acpi_aml_read,
        .write          = acpi_aml_write,
        .poll           = acpi_aml_poll,
        .open           = acpi_aml_open,
        .release        = acpi_aml_release,
        .llseek         = generic_file_llseek,
};

static const struct acpi_debugger_ops acpi_aml_debugger = {
        .create_thread           = acpi_aml_create_thread,
        .read_cmd                = acpi_aml_read_cmd,
        .write_log               = acpi_aml_write_log,
        .wait_command_ready      = acpi_aml_wait_command_ready,
        .notify_command_complete = acpi_aml_notify_command_complete,
};

int __init acpi_aml_init(void)
{
        int ret = 0;

        if (!acpi_debugfs_dir) {
                ret = -ENOENT;
                goto err_exit;
        }

        /* Initialize AML IO interface */
        mutex_init(&acpi_aml_io.lock);
        init_waitqueue_head(&acpi_aml_io.wait);
        acpi_aml_io.out_crc.buf = acpi_aml_io.out_buf;
        acpi_aml_io.in_crc.buf = acpi_aml_io.in_buf;
        acpi_aml_dentry = debugfs_create_file("acpidbg",
                                              S_IFREG | S_IRUGO | S_IWUSR,
                                              acpi_debugfs_dir, NULL,
                                              &acpi_aml_operations);
        if (acpi_aml_dentry == NULL) {
                ret = -ENODEV;
                goto err_exit;
        }
        ret = acpi_register_debugger(THIS_MODULE, &acpi_aml_debugger);
        if (ret)
                goto err_fs;
        acpi_aml_initialized = true;

err_fs:
        if (ret) {
                debugfs_remove(acpi_aml_dentry);
                acpi_aml_dentry = NULL;
        }
err_exit:
        return ret;
}

void __exit acpi_aml_exit(void)
{
        if (acpi_aml_initialized) {
                acpi_unregister_debugger(&acpi_aml_debugger);
                if (acpi_aml_dentry) {
                        debugfs_remove(acpi_aml_dentry);
                        acpi_aml_dentry = NULL;
                }
                acpi_aml_initialized = false;
        }
}

module_init(acpi_aml_init);
module_exit(acpi_aml_exit);

MODULE_AUTHOR("Lv Zheng");
MODULE_DESCRIPTION("ACPI debugger userspace IO driver");
MODULE_LICENSE("GPL");