/*
 * Copyright (C) 2011 Google, Inc.
 * Copyright (C) 2012 Intel, Inc.
 * Copyright (C) 2013 Intel, Inc.
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

/* This source file contains the implementation of a special device driver
 * that intends to provide a *very* fast communication channel between the
 * guest system and the QEMU emulator.
 *
 * Usage from the guest is simply the following (error handling simplified):
 *
 *    int  fd = open("/dev/qemu_pipe",O_RDWR);
 *    .... write() or read() through the pipe.
 *
 * This driver doesn't deal with the exact protocol used during the session.
 * It is intended to be as simple as something like:
 *
 *    // do this _just_ after opening the fd to connect to a specific
 *    // emulator service.
 *    const char*  msg = "<pipename>";
 *    if (write(fd, msg, strlen(msg)+1) < 0) {
 *       ... could not connect to <pipename> service
 *       close(fd);
 *    }
 *
 *    // after this, simply read() and write() to communicate with the
 *    // service. Exact protocol details left as an exercise to the reader.
 *
 * This driver is very fast because it doesn't copy any data through
 * intermediate buffers, since the emulator is capable of translating
 * guest user addresses into host ones.
 *
 * Note that we must however ensure that each user page involved in the
 * exchange is properly mapped during a transfer.
 */

#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/miscdevice.h>
#include <linux/platform_device.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/io.h>

/*
 * IMPORTANT: The following constants must match the ones used and defined
 * in external/qemu/hw/goldfish_pipe.c in the Android source tree.
 */

/* pipe device registers */
#define PIPE_REG_COMMAND                0x00  /* write: value = command */
#define PIPE_REG_STATUS                 0x04  /* read */
#define PIPE_REG_CHANNEL                0x08  /* read/write: channel id */
#define PIPE_REG_SIZE                   0x0c  /* read/write: buffer size */
#define PIPE_REG_ADDRESS                0x10  /* write: physical address */
#define PIPE_REG_WAKES                  0x14  /* read: wake flags */
#define PIPE_REG_PARAMS_ADDR_LOW        0x18  /* read/write: batch data address */
#define PIPE_REG_PARAMS_ADDR_HIGH       0x1c  /* read/write: batch data address */
#define PIPE_REG_ACCESS_PARAMS          0x20  /* write: batch access */

/* list of commands for PIPE_REG_COMMAND */
#define CMD_OPEN                        1  /* open new channel */
#define CMD_CLOSE                       2  /* close channel (from guest) */
#define CMD_POLL                        3  /* poll read/write status */

/* List of bitflags returned in status of CMD_POLL command */
#define PIPE_POLL_IN                    (1 << 0)
#define PIPE_POLL_OUT                   (1 << 1)
#define PIPE_POLL_HUP                   (1 << 2)

/* The following commands are related to write operations */
#define CMD_WRITE_BUFFER        4  /* send a user buffer to the emulator */
#define CMD_WAKE_ON_WRITE       5  /* tell the emulator to wake us when writing
                                     is possible */

/* The following commands are related to read operations, they must be
 * listed in the same order than the corresponding write ones, since we
 * will use (CMD_READ_BUFFER - CMD_WRITE_BUFFER) as a special offset
 * in goldfish_pipe_read_write() below.
 */
#define CMD_READ_BUFFER        6  /* receive a user buffer from the emulator */
#define CMD_WAKE_ON_READ       7  /* tell the emulator to wake us when reading
                                   * is possible */

/* Possible status values used to signal errors - see goldfish_pipe_error_convert */
#define PIPE_ERROR_INVAL       -1
#define PIPE_ERROR_AGAIN       -2
#define PIPE_ERROR_NOMEM       -3
#define PIPE_ERROR_IO          -4

/* Bit-flags used to signal events from the emulator */
#define PIPE_WAKE_CLOSED       (1 << 0)  /* emulator closed pipe */
#define PIPE_WAKE_READ         (1 << 1)  /* pipe can now be read from */
#define PIPE_WAKE_WRITE        (1 << 2)  /* pipe can now be written to */

struct access_params {
        u32 channel;
        u32 size;
        u32 address;
        u32 cmd;
        u32 result;
        /* reserved for future extension */
        u32 flags;
};

/* The global driver data. Holds a reference to the i/o page used to
 * communicate with the emulator, and a wake queue for blocked tasks
 * waiting to be awoken.
 */
struct goldfish_pipe_dev {
        spinlock_t lock;
        unsigned char __iomem *base;
        struct access_params *aps;
        int irq;
};

static struct goldfish_pipe_dev   pipe_dev[1];

/* This data type models a given pipe instance */
struct goldfish_pipe {
        struct goldfish_pipe_dev *dev;
        struct mutex lock;
        unsigned long flags;
        wait_queue_head_t wake_queue;
};


/* Bit flags for the 'flags' field */
enum {
        BIT_CLOSED_ON_HOST = 0,  /* pipe closed by host */
        BIT_WAKE_ON_WRITE  = 1,  /* want to be woken on writes */
        BIT_WAKE_ON_READ   = 2,  /* want to be woken on reads */
};


static u32 goldfish_cmd_status(struct goldfish_pipe *pipe, u32 cmd)
{ 
        unsigned long flags;
        u32 status;
        struct goldfish_pipe_dev *dev = pipe->dev;

        spin_lock_irqsave(&dev->lock, flags);
        writel((u32)pipe, dev->base + PIPE_REG_CHANNEL);
        writel(cmd, dev->base + PIPE_REG_COMMAND);
        status = readl(dev->base + PIPE_REG_STATUS);
        spin_unlock_irqrestore(&dev->lock, flags);
        return status;
}

static void goldfish_cmd(struct goldfish_pipe *pipe, u32 cmd)
{ 
        unsigned long flags;
        struct goldfish_pipe_dev *dev = pipe->dev;

        spin_lock_irqsave(&dev->lock, flags);
        writel((u32)pipe, dev->base + PIPE_REG_CHANNEL);
        writel(cmd, dev->base + PIPE_REG_COMMAND);
        spin_unlock_irqrestore(&dev->lock, flags);
}

/* This function converts an error code returned by the emulator through
 * the PIPE_REG_STATUS i/o register into a valid negative errno value.
 */
static int goldfish_pipe_error_convert(int status)
{
        switch (status) {
        case PIPE_ERROR_AGAIN:
                return -EAGAIN;
        case PIPE_ERROR_NOMEM:
                return -ENOMEM;
        case PIPE_ERROR_IO:
                return -EIO;
        default:
                return -EINVAL;
        }
}

/*
 * Notice: QEMU will return 0 for un-known register access, indicating
 * param_acess is supported or not
 */
static int valid_batchbuffer_addr(struct goldfish_pipe_dev *dev,
                                  struct access_params *aps)
{
        u32 aph, apl;
        u64 paddr;
        aph = readl(dev->base + PIPE_REG_PARAMS_ADDR_HIGH);
        apl = readl(dev->base + PIPE_REG_PARAMS_ADDR_LOW);

        paddr = ((u64)aph << 32) | apl;
        if (paddr != (__pa(aps)))
                return 0;
        return 1;
}

/* 0 on success */
static int setup_access_params_addr(struct platform_device *pdev,
                                        struct goldfish_pipe_dev *dev)
{
        u64 paddr;
        struct access_params *aps;

        aps = devm_kzalloc(&pdev->dev, sizeof(struct access_params), GFP_KERNEL);
        if (!aps)
                return -1;

        /* FIXME */
        paddr = __pa(aps);
        writel((u32)(paddr >> 32), dev->base + PIPE_REG_PARAMS_ADDR_HIGH);
        writel((u32)paddr, dev->base + PIPE_REG_PARAMS_ADDR_LOW);

        if (valid_batchbuffer_addr(dev, aps)) {
                dev->aps = aps;
                return 0;
        } else
                return -1;
}

/* A value that will not be set by qemu emulator */
#define INITIAL_BATCH_RESULT (0xdeadbeaf)
static int access_with_param(struct goldfish_pipe_dev *dev, const int cmd,
                                unsigned long address, unsigned long avail,
                                struct goldfish_pipe *pipe, int *status)
{
        struct access_params *aps = dev->aps;

        if (aps == NULL)
                return -1;

        aps->result = INITIAL_BATCH_RESULT;
        aps->channel = (unsigned long)pipe;
        aps->size = avail;
        aps->address = address;
        aps->cmd = cmd;
        writel(cmd, dev->base + PIPE_REG_ACCESS_PARAMS);
        /*
         * If the aps->result has not changed, that means
         * that the batch command failed
         */
        if (aps->result == INITIAL_BATCH_RESULT)
                return -1;
        *status = aps->result;
        return 0;
}

/* This function is used for both reading from and writing to a given
 * pipe.
 */
static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
                                    size_t bufflen, int is_write)
{
        unsigned long irq_flags;
        struct goldfish_pipe *pipe = filp->private_data;
        struct goldfish_pipe_dev *dev = pipe->dev;
        const int cmd_offset = is_write ? 0
                                        : (CMD_READ_BUFFER - CMD_WRITE_BUFFER);
        unsigned long address, address_end;
        int ret = 0;

        /* If the emulator already closed the pipe, no need to go further */
        if (test_bit(BIT_CLOSED_ON_HOST, &pipe->flags))
                return -EIO;

        /* Null reads or writes succeeds */
        if (unlikely(bufflen) == 0)
                return 0;

        /* Check the buffer range for access */
        if (!access_ok(is_write ? VERIFY_WRITE : VERIFY_READ,
                        buffer, bufflen))
                return -EFAULT;

        /* Serialize access to the pipe */
        if (mutex_lock_interruptible(&pipe->lock))
                return -ERESTARTSYS;

        address = (unsigned long)(void *)buffer;
        address_end = address + bufflen;

        while (address < address_end) {
                unsigned long  page_end = (address & PAGE_MASK) + PAGE_SIZE;
                unsigned long  next     = page_end < address_end ? page_end
                                                                 : address_end;
                unsigned long  avail    = next - address;
                int status, wakeBit;

                /* Ensure that the corresponding page is properly mapped */
                /* FIXME: this isn't safe or sufficient - use get_user_pages */
                if (is_write) {
                        char c;
                        /* Ensure that the page is mapped and readable */
                        if (__get_user(c, (char __user *)address)) {
                                if (!ret)
                                        ret = -EFAULT;
                                break;
                        }
                } else {
                        /* Ensure that the page is mapped and writable */
                        if (__put_user(0, (char __user *)address)) {
                                if (!ret)
                                        ret = -EFAULT;
                                break;
                        }
                }

                /* Now, try to transfer the bytes in the current page */
                spin_lock_irqsave(&dev->lock, irq_flags);
                if (access_with_param(dev, CMD_WRITE_BUFFER + cmd_offset,
                                address, avail, pipe, &status)) {
                        writel((u32)pipe, dev->base + PIPE_REG_CHANNEL);
                        writel(avail, dev->base + PIPE_REG_SIZE);
                        writel(address, dev->base + PIPE_REG_ADDRESS);
                        writel(CMD_WRITE_BUFFER + cmd_offset,
                                        dev->base + PIPE_REG_COMMAND);
                        status = readl(dev->base + PIPE_REG_STATUS);
                }
                spin_unlock_irqrestore(&dev->lock, irq_flags);

                if (status > 0) { /* Correct transfer */
                        ret += status;
                        address += status;
                        continue;
                }

                if (status == 0)  /* EOF */
                        break;

                /* An error occured. If we already transfered stuff, just
                * return with its count. We expect the next call to return
                * an error code */
                if (ret > 0)
                        break;

                /* If the error is not PIPE_ERROR_AGAIN, or if we are not in
                * non-blocking mode, just return the error code.
                */
                if (status != PIPE_ERROR_AGAIN ||
                        (filp->f_flags & O_NONBLOCK) != 0) {
                        ret = goldfish_pipe_error_convert(status);
                        break;
                }

                /* We will have to wait until more data/space is available.
                * First, mark the pipe as waiting for a specific wake signal.
                */
                wakeBit = is_write ? BIT_WAKE_ON_WRITE : BIT_WAKE_ON_READ;
                set_bit(wakeBit, &pipe->flags);

                /* Tell the emulator we're going to wait for a wake event */
                goldfish_cmd(pipe, CMD_WAKE_ON_WRITE + cmd_offset);

                /* Unlock the pipe, then wait for the wake signal */
                mutex_unlock(&pipe->lock);

                while (test_bit(wakeBit, &pipe->flags)) {
                        if (wait_event_interruptible(
                                        pipe->wake_queue,
                                        !test_bit(wakeBit, &pipe->flags)))
                                return -ERESTARTSYS;

                        if (test_bit(BIT_CLOSED_ON_HOST, &pipe->flags))
                                return -EIO;
                }

                /* Try to re-acquire the lock */
                if (mutex_lock_interruptible(&pipe->lock))
                        return -ERESTARTSYS;

                /* Try the transfer again */
                continue;
        }
        mutex_unlock(&pipe->lock);
        return ret;
}

static ssize_t goldfish_pipe_read(struct file *filp, char __user *buffer,
                              size_t bufflen, loff_t *ppos)
{
        return goldfish_pipe_read_write(filp, buffer, bufflen, 0);
}

static ssize_t goldfish_pipe_write(struct file *filp,
                                const char __user *buffer, size_t bufflen,
                                loff_t *ppos)
{
        return goldfish_pipe_read_write(filp, (char __user *)buffer,
                                                                bufflen, 1);
}


static unsigned int goldfish_pipe_poll(struct file *filp, poll_table *wait)
{
        struct goldfish_pipe *pipe = filp->private_data;
        unsigned int mask = 0;
        int status;

        mutex_lock(&pipe->lock);

        poll_wait(filp, &pipe->wake_queue, wait);

        status = goldfish_cmd_status(pipe, CMD_POLL);

        mutex_unlock(&pipe->lock);

        if (status & PIPE_POLL_IN)
                mask |= POLLIN | POLLRDNORM;

        if (status & PIPE_POLL_OUT)
                mask |= POLLOUT | POLLWRNORM;

        if (status & PIPE_POLL_HUP)
                mask |= POLLHUP;

        if (test_bit(BIT_CLOSED_ON_HOST, &pipe->flags))
                mask |= POLLERR;

        return mask;
}

static irqreturn_t goldfish_pipe_interrupt(int irq, void *dev_id)
{
        struct goldfish_pipe_dev *dev = dev_id;
        unsigned long irq_flags;
        int count = 0;

        /* We're going to read from the emulator a list of (channel,flags)
        * pairs corresponding to the wake events that occured on each
        * blocked pipe (i.e. channel).
        */
        spin_lock_irqsave(&dev->lock, irq_flags);
        for (;;) {
                /* First read the channel, 0 means the end of the list */
                struct goldfish_pipe *pipe;
                unsigned long wakes;
                unsigned long channel = readl(dev->base + PIPE_REG_CHANNEL);

                if (channel == 0)
                        break;

                /* Convert channel to struct pipe pointer + read wake flags */
                wakes = readl(dev->base + PIPE_REG_WAKES);
                pipe  = (struct goldfish_pipe *)(ptrdiff_t)channel;

                /* Did the emulator just closed a pipe? */
                if (wakes & PIPE_WAKE_CLOSED) {
                        set_bit(BIT_CLOSED_ON_HOST, &pipe->flags);
                        wakes |= PIPE_WAKE_READ | PIPE_WAKE_WRITE;
                }
                if (wakes & PIPE_WAKE_READ)
                        clear_bit(BIT_WAKE_ON_READ, &pipe->flags);
                if (wakes & PIPE_WAKE_WRITE)
                        clear_bit(BIT_WAKE_ON_WRITE, &pipe->flags);

                wake_up_interruptible(&pipe->wake_queue);
                count++;
        }
        spin_unlock_irqrestore(&dev->lock, irq_flags);

        return (count == 0) ? IRQ_NONE : IRQ_HANDLED;
}

/**
 *      goldfish_pipe_open      -       open a channel to the AVD
 *      @inode: inode of device
 *      @file: file struct of opener
 *
 *      Create a new pipe link between the emulator and the use application.
 *      Each new request produces a new pipe.
 *
 *      Note: we use the pipe ID as a mux. All goldfish emulations are 32bit
 *      right now so this is fine. A move to 64bit will need this addressing
 */
static int goldfish_pipe_open(struct inode *inode, struct file *file)
{
        struct goldfish_pipe *pipe;
        struct goldfish_pipe_dev *dev = pipe_dev;
        int32_t status;

        /* Allocate new pipe kernel object */
        pipe = kzalloc(sizeof(*pipe), GFP_KERNEL);
        if (pipe == NULL)
                return -ENOMEM;

        pipe->dev = dev;
        mutex_init(&pipe->lock);
        init_waitqueue_head(&pipe->wake_queue);

        /*
         * Now, tell the emulator we're opening a new pipe. We use the
         * pipe object's address as the channel identifier for simplicity.
         */

        status = goldfish_cmd_status(pipe, CMD_OPEN);
        if (status < 0) {
                kfree(pipe);
                return status;
        }

        /* All is done, save the pipe into the file's private data field */
        file->private_data = pipe;
        return 0;
}

static int goldfish_pipe_release(struct inode *inode, struct file *filp)
{
        struct goldfish_pipe *pipe = filp->private_data;

        /* The guest is closing the channel, so tell the emulator right now */
        goldfish_cmd(pipe, CMD_CLOSE);
        kfree(pipe);
        filp->private_data = NULL;
        return 0;
}

static const struct file_operations goldfish_pipe_fops = {
        .owner = THIS_MODULE,
        .read = goldfish_pipe_read,
        .write = goldfish_pipe_write,
        .poll = goldfish_pipe_poll,
        .open = goldfish_pipe_open,
        .release = goldfish_pipe_release,
};

static struct miscdevice goldfish_pipe_device = {
        .minor = MISC_DYNAMIC_MINOR,
        .name = "goldfish_pipe",
        .fops = &goldfish_pipe_fops,
};

static int goldfish_pipe_probe(struct platform_device *pdev)
{
        int err;
        struct resource *r;
        struct goldfish_pipe_dev *dev = pipe_dev;

        /* not thread safe, but this should not happen */
        WARN_ON(dev->base != NULL);

        spin_lock_init(&dev->lock);

        r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (r == NULL || resource_size(r) < PAGE_SIZE) {
                dev_err(&pdev->dev, "can't allocate i/o page\n");
                return -EINVAL;
        }
        dev->base = devm_ioremap(&pdev->dev, r->start, PAGE_SIZE);
        if (dev->base == NULL) {
                dev_err(&pdev->dev, "ioremap failed\n");
                return -EINVAL;
        }

        r = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
        if (r == NULL) {
                err = -EINVAL;
                goto error;
        }
        dev->irq = r->start;

        err = devm_request_irq(&pdev->dev, dev->irq, goldfish_pipe_interrupt,
                                IRQF_SHARED, "goldfish_pipe", dev);
        if (err) {
                dev_err(&pdev->dev, "unable to allocate IRQ\n");
                goto error;
        }

        err = misc_register(&goldfish_pipe_device);
        if (err) {
                dev_err(&pdev->dev, "unable to register device\n");
                goto error;
        }
        setup_access_params_addr(pdev, dev);
        return 0;

error:
        dev->base = NULL;
        return err;
}

static int goldfish_pipe_remove(struct platform_device *pdev)
{
        struct goldfish_pipe_dev *dev = pipe_dev;
        misc_deregister(&goldfish_pipe_device);
        dev->base = NULL;
        return 0;
}

static struct platform_driver goldfish_pipe = {
        .probe = goldfish_pipe_probe,
        .remove = goldfish_pipe_remove,
        .driver = {
                .name = "goldfish_pipe"
        }
};

module_platform_driver(goldfish_pipe);
MODULE_AUTHOR("David Turner <digit@google.com>");
MODULE_LICENSE("GPL");