Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / drivers / platform / goldfish / goldfish_pipe.c

/*
 * Copyright (C) 2012 Intel, Inc.
 * Copyright (C) 2013 Intel, Inc.
 * Copyright (C) 2014 Linaro Limited
 * Copyright (C) 2011-2016 Google, 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>
#include <linux/goldfish.h>
#include <linux/dma-mapping.h>
#include <linux/mm.h>
#include <linux/acpi.h>

/*
 * Update this when something changes in the driver's behavior so the host
 * can benefit from knowing it
 */
enum {
        PIPE_DRIVER_VERSION = 2,
        PIPE_CURRENT_DEVICE_VERSION = 2
};

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

/* List of bitflags returned in status of CMD_POLL command */
enum PipePollFlags {
        PIPE_POLL_IN    = 1 << 0,
        PIPE_POLL_OUT   = 1 << 1,
        PIPE_POLL_HUP   = 1 << 2
};

/* Possible status values used to signal errors - see goldfish_pipe_error_convert */
enum PipeErrors {
        PIPE_ERROR_INVAL  = -1,
        PIPE_ERROR_AGAIN  = -2,
        PIPE_ERROR_NOMEM  = -3,
        PIPE_ERROR_IO     = -4
};

/* Bit-flags used to signal events from the emulator */
enum PipeWakeFlags {
        PIPE_WAKE_CLOSED = 1 << 0,  /* emulator closed pipe */
        PIPE_WAKE_READ   = 1 << 1,  /* pipe can now be read from */
        PIPE_WAKE_WRITE  = 1 << 2  /* pipe can now be written to */
};

/* Bit flags for the 'flags' field */
enum PipeFlagsBits {
        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 */
};

enum PipeRegs {
        PIPE_REG_CMD = 0,

        PIPE_REG_SIGNAL_BUFFER_HIGH = 4,
        PIPE_REG_SIGNAL_BUFFER = 8,
        PIPE_REG_SIGNAL_BUFFER_COUNT = 12,

        PIPE_REG_OPEN_BUFFER_HIGH = 20,
        PIPE_REG_OPEN_BUFFER = 24,

        PIPE_REG_VERSION = 36,

        PIPE_REG_GET_SIGNALLED = 48,
};

enum PipeCmdCode {
        PIPE_CMD_OPEN = 1,      /* to be used by the pipe device itself */
        PIPE_CMD_CLOSE,
        PIPE_CMD_POLL,
        PIPE_CMD_WRITE,
        PIPE_CMD_WAKE_ON_WRITE,
        PIPE_CMD_READ,
        PIPE_CMD_WAKE_ON_READ,

        /*
         * TODO(zyy): implement a deferred read/write execution to allow
         * parallel processing of pipe operations on the host.
         */
        PIPE_CMD_WAKE_ON_DONE_IO,
};

enum {
        MAX_BUFFERS_PER_COMMAND = 336,
        MAX_SIGNALLED_PIPES = 64,
        INITIAL_PIPES_CAPACITY = 64
};

struct goldfish_pipe_dev;
struct goldfish_pipe;
struct goldfish_pipe_command;

/* A per-pipe command structure, shared with the host */
struct goldfish_pipe_command {
        s32 cmd;                /* PipeCmdCode, guest -> host */
        s32 id;                 /* pipe id, guest -> host */
        s32 status;             /* command execution status, host -> guest */
        s32 reserved;   /* to pad to 64-bit boundary */
        union {
                /* Parameters for PIPE_CMD_{READ,WRITE} */
                struct {
                        /* number of buffers, guest -> host */
                        u32 buffers_count;
                        /* number of consumed bytes, host -> guest */
                        s32 consumed_size;
                        /* buffer pointers, guest -> host */
                        u64 ptrs[MAX_BUFFERS_PER_COMMAND];
                        /* buffer sizes, guest -> host */
                        u32 sizes[MAX_BUFFERS_PER_COMMAND];
                } rw_params;
        };
};

/* A single signalled pipe information */
struct signalled_pipe_buffer {
        u32 id;
        u32 flags;
};

/* Parameters for the PIPE_CMD_OPEN command */
struct open_command_param {
        u64 command_buffer_ptr;
        u32 rw_params_max_count;
};

/* Device-level set of buffers shared with the host */
struct goldfish_pipe_dev_buffers {
        struct open_command_param open_command_params;
        struct signalled_pipe_buffer signalled_pipe_buffers[
                MAX_SIGNALLED_PIPES];
};

/* This data type models a given pipe instance */
struct goldfish_pipe {
        /* pipe ID - index into goldfish_pipe_dev::pipes array */
        u32 id;
        /* The wake flags pipe is waiting for
         * Note: not protected with any lock, uses atomic operations
         *  and barriers to make it thread-safe.
         */
        unsigned long flags;
        /* wake flags host have signalled,
         *  - protected by goldfish_pipe_dev::lock
         */
        unsigned long signalled_flags;

        /* A pointer to command buffer */
        struct goldfish_pipe_command *command_buffer;

        /* doubly linked list of signalled pipes, protected by
         * goldfish_pipe_dev::lock
         */
        struct goldfish_pipe *prev_signalled;
        struct goldfish_pipe *next_signalled;

        /*
         * A pipe's own lock. Protects the following:
         *  - *command_buffer - makes sure a command can safely write its
         *    parameters to the host and read the results back.
         */
        struct mutex lock;

        /* A wake queue for sleeping until host signals an event */
        wait_queue_head_t wake_queue;
        /* Pointer to the parent goldfish_pipe_dev instance */
        struct goldfish_pipe_dev *dev;
};

/* 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 {
        /*
         * Global device spinlock. Protects the following members:
         *  - pipes, pipes_capacity
         *  - [*pipes, *pipes + pipes_capacity) - array data
         *  - first_signalled_pipe,
         *      goldfish_pipe::prev_signalled,
         *      goldfish_pipe::next_signalled,
         *      goldfish_pipe::signalled_flags - all singnalled-related fields,
         *                                       in all allocated pipes
         *  - open_command_params - PIPE_CMD_OPEN-related buffers
         *
         * It looks like a lot of different fields, but the trick is that
         * the only operation that happens often is the signalled pipes array
         * manipulation. That's why it's OK for now to keep the rest of the
         * fields under the same lock. If we notice too much contention because
         * of PIPE_CMD_OPEN, then we should add a separate lock there.
         */
        spinlock_t lock;

        /*
         * Array of the pipes of |pipes_capacity| elements,
         * indexed by goldfish_pipe::id
         */
        struct goldfish_pipe **pipes;
        u32 pipes_capacity;

        /* Pointers to the buffers host uses for interaction with this driver */
        struct goldfish_pipe_dev_buffers *buffers;

        /* Head of a doubly linked list of signalled pipes */
        struct goldfish_pipe *first_signalled_pipe;

        /* Some device-specific data */
        int irq;
        int version;
        unsigned char __iomem *base;
};

static struct goldfish_pipe_dev pipe_dev[1] = {};

static int goldfish_cmd_locked(struct goldfish_pipe *pipe, enum PipeCmdCode cmd)
{
        pipe->command_buffer->cmd = cmd;
        /* failure by default */
        pipe->command_buffer->status = PIPE_ERROR_INVAL;
        writel(pipe->id, pipe->dev->base + PIPE_REG_CMD);
        return pipe->command_buffer->status;
}

static int goldfish_cmd(struct goldfish_pipe *pipe, enum PipeCmdCode cmd)
{
        int status;

        if (mutex_lock_interruptible(&pipe->lock))
                return PIPE_ERROR_IO;
        status = goldfish_cmd_locked(pipe, cmd);
        mutex_unlock(&pipe->lock);
        return status;
}

/*
 * 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;
        }
}

static int pin_user_pages(unsigned long first_page, unsigned long last_page,
        unsigned int last_page_size, int is_write,
        struct page *pages[MAX_BUFFERS_PER_COMMAND],
        unsigned int *iter_last_page_size)
{
        int ret;
        int requested_pages = ((last_page - first_page) >> PAGE_SHIFT) + 1;

        if (requested_pages > MAX_BUFFERS_PER_COMMAND) {
                requested_pages = MAX_BUFFERS_PER_COMMAND;
                *iter_last_page_size = PAGE_SIZE;
        } else {
                *iter_last_page_size = last_page_size;
        }

        ret = get_user_pages_fast(
                        first_page, requested_pages, !is_write, pages);
        if (ret <= 0)
                return -EFAULT;
        if (ret < requested_pages)
                *iter_last_page_size = PAGE_SIZE;
        return ret;

}

static void release_user_pages(struct page **pages, int pages_count,
        int is_write, s32 consumed_size)
{
        int i;

        for (i = 0; i < pages_count; i++) {
                if (!is_write && consumed_size > 0)
                        set_page_dirty(pages[i]);
                put_page(pages[i]);
        }
}

/* Populate the call parameters, merging adjacent pages together */
static void populate_rw_params(
        struct page **pages, int pages_count,
        unsigned long address, unsigned long address_end,
        unsigned long first_page, unsigned long last_page,
        unsigned int iter_last_page_size, int is_write,
        struct goldfish_pipe_command *command)
{
        /*
         * Process the first page separately - it's the only page that
         * needs special handling for its start address.
         */
        unsigned long xaddr = page_to_phys(pages[0]);
        unsigned long xaddr_prev = xaddr;
        int buffer_idx = 0;
        int i = 1;
        int size_on_page = first_page == last_page
                        ? (int)(address_end - address)
                        : (PAGE_SIZE - (address & ~PAGE_MASK));
        command->rw_params.ptrs[0] = (u64)(xaddr | (address & ~PAGE_MASK));
        command->rw_params.sizes[0] = size_on_page;
        for (; i < pages_count; ++i) {
                xaddr = page_to_phys(pages[i]);
                size_on_page = (i == pages_count - 1) ?
                        iter_last_page_size : PAGE_SIZE;
                if (xaddr == xaddr_prev + PAGE_SIZE) {
                        command->rw_params.sizes[buffer_idx] += size_on_page;
                } else {
                        ++buffer_idx;
                        command->rw_params.ptrs[buffer_idx] = (u64)xaddr;
                        command->rw_params.sizes[buffer_idx] = size_on_page;
                }
                xaddr_prev = xaddr;
        }
        command->rw_params.buffers_count = buffer_idx + 1;
}

static int transfer_max_buffers(struct goldfish_pipe *pipe,
        unsigned long address, unsigned long address_end, int is_write,
        unsigned long last_page, unsigned int last_page_size,
        s32 *consumed_size, int *status)
{
        static struct page *pages[MAX_BUFFERS_PER_COMMAND];
        unsigned long first_page = address & PAGE_MASK;
        unsigned int iter_last_page_size;
        int pages_count = pin_user_pages(first_page, last_page,
                        last_page_size, is_write,
                        pages, &iter_last_page_size);

        if (pages_count < 0)
                return pages_count;

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

        populate_rw_params(pages, pages_count, address, address_end,
                first_page, last_page, iter_last_page_size, is_write,
                pipe->command_buffer);

        /* Transfer the data */
        *status = goldfish_cmd_locked(pipe,
                                is_write ? PIPE_CMD_WRITE : PIPE_CMD_READ);

        *consumed_size = pipe->command_buffer->rw_params.consumed_size;

        release_user_pages(pages, pages_count, is_write, *consumed_size);

        mutex_unlock(&pipe->lock);

        return 0;
}

static int wait_for_host_signal(struct goldfish_pipe *pipe, int is_write)
{
        u32 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 */
        (void)goldfish_cmd(pipe,
                is_write ? PIPE_CMD_WAKE_ON_WRITE : PIPE_CMD_WAKE_ON_READ);

        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;
        }

        return 0;
}

static ssize_t goldfish_pipe_read_write(struct file *filp,
        char __user *buffer, size_t bufflen, int is_write)
{
        struct goldfish_pipe *pipe = filp->private_data;
        int count = 0, ret = -EINVAL;
        unsigned long address, address_end, last_page;
        unsigned int last_page_size;

        /* If the emulator already closed the pipe, no need to go further */
        if (unlikely(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 (unlikely(!access_ok(is_write ? VERIFY_WRITE : VERIFY_READ,
                        buffer, bufflen)))
                return -EFAULT;

        address = (unsigned long)buffer;
        address_end = address + bufflen;
        last_page = (address_end - 1) & PAGE_MASK;
        last_page_size = ((address_end - 1) & ~PAGE_MASK) + 1;

        while (address < address_end) {
                s32 consumed_size;
                int status;

                ret = transfer_max_buffers(pipe, address, address_end, is_write,
                                last_page, last_page_size, &consumed_size,
                                &status);
                if (ret < 0)
                        break;

                if (consumed_size > 0) {
                        /* No matter what's the status, we've transferred
                         * something.
                         */
                        count += consumed_size;
                        address += consumed_size;
                }
                if (status > 0)
                        continue;
                if (status == 0) {
                        /* EOF */
                        ret = 0;
                        break;
                }
                if (count > 0) {
                        /*
                         * An error occurred, but we already transferred
                         * something on one of the previous iterations.
                         * Just return what we already copied and log this
                         * err.
                         */
                        if (status != PIPE_ERROR_AGAIN)
                                pr_info_ratelimited("goldfish_pipe: backend error %d on %s\n",
                                        status, is_write ? "write" : "read");
                        break;
                }

                /*
                 * If the error is not PIPE_ERROR_AGAIN, or if we are 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;
                }

                status = wait_for_host_signal(pipe, is_write);
                if (status < 0)
                        return status;
        }

        if (count > 0)
                return count;
        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,
                        /* is_write */ 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,
                        /* cast away the const */(char __user *)buffer, bufflen,
                        /* is_write */ 1);
}

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

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

        status = goldfish_cmd(pipe, PIPE_CMD_POLL);
        if (status < 0)
                return -ERESTARTSYS;

        if (status & PIPE_POLL_IN)
                mask |= EPOLLIN | EPOLLRDNORM;
        if (status & PIPE_POLL_OUT)
                mask |= EPOLLOUT | EPOLLWRNORM;
        if (status & PIPE_POLL_HUP)
                mask |= EPOLLHUP;
        if (test_bit(BIT_CLOSED_ON_HOST, &pipe->flags))
                mask |= EPOLLERR;

        return mask;
}

static void signalled_pipes_add_locked(struct goldfish_pipe_dev *dev,
        u32 id, u32 flags)
{
        struct goldfish_pipe *pipe;

        if (WARN_ON(id >= dev->pipes_capacity))
                return;

        pipe = dev->pipes[id];
        if (!pipe)
                return;
        pipe->signalled_flags |= flags;

        if (pipe->prev_signalled || pipe->next_signalled
                || dev->first_signalled_pipe == pipe)
                return; /* already in the list */
        pipe->next_signalled = dev->first_signalled_pipe;
        if (dev->first_signalled_pipe)
                dev->first_signalled_pipe->prev_signalled = pipe;
        dev->first_signalled_pipe = pipe;
}

static void signalled_pipes_remove_locked(struct goldfish_pipe_dev *dev,
        struct goldfish_pipe *pipe) {
        if (pipe->prev_signalled)
                pipe->prev_signalled->next_signalled = pipe->next_signalled;
        if (pipe->next_signalled)
                pipe->next_signalled->prev_signalled = pipe->prev_signalled;
        if (pipe == dev->first_signalled_pipe)
                dev->first_signalled_pipe = pipe->next_signalled;
        pipe->prev_signalled = NULL;
        pipe->next_signalled = NULL;
}

static struct goldfish_pipe *signalled_pipes_pop_front(
                struct goldfish_pipe_dev *dev, int *wakes)
{
        struct goldfish_pipe *pipe;
        unsigned long flags;

        spin_lock_irqsave(&dev->lock, flags);

        pipe = dev->first_signalled_pipe;
        if (pipe) {
                *wakes = pipe->signalled_flags;
                pipe->signalled_flags = 0;
                /*
                 * This is an optimized version of
                 * signalled_pipes_remove_locked()
                 * - We want to make it as fast as possible to
                 * wake the sleeping pipe operations faster.
                 */
                dev->first_signalled_pipe = pipe->next_signalled;
                if (dev->first_signalled_pipe)
                        dev->first_signalled_pipe->prev_signalled = NULL;
                pipe->next_signalled = NULL;
        }

        spin_unlock_irqrestore(&dev->lock, flags);
        return pipe;
}

static void goldfish_interrupt_task(unsigned long unused)
{
        struct goldfish_pipe_dev *dev = pipe_dev;
        /* Iterate over the signalled pipes and wake them one by one */
        struct goldfish_pipe *pipe;
        int wakes;

        while ((pipe = signalled_pipes_pop_front(dev, &wakes)) != NULL) {
                if (wakes & PIPE_WAKE_CLOSED) {
                        pipe->flags = 1 << BIT_CLOSED_ON_HOST;
                } else {
                        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() implies a write barrier, so don't
                 * explicitly add another one here.
                 */
                wake_up_interruptible(&pipe->wake_queue);
        }
}
DECLARE_TASKLET(goldfish_interrupt_tasklet, goldfish_interrupt_task, 0);

/*
 * The general idea of the interrupt handling:
 *
 *  1. device raises an interrupt if there's at least one signalled pipe
 *  2. IRQ handler reads the signalled pipes and their count from the device
 *  3. device writes them into a shared buffer and returns the count
 *      it only resets the IRQ if it has returned all signalled pipes,
 *      otherwise it leaves it raised, so IRQ handler will be called
 *      again for the next chunk
 *  4. IRQ handler adds all returned pipes to the device's signalled pipes list
 *  5. IRQ handler launches a tasklet to process the signalled pipes from the
 *      list in a separate context
 */
static irqreturn_t goldfish_pipe_interrupt(int irq, void *dev_id)
{
        u32 count;
        u32 i;
        unsigned long flags;
        struct goldfish_pipe_dev *dev = dev_id;

        if (dev != pipe_dev)
                return IRQ_NONE;

        /* Request the signalled pipes from the device */
        spin_lock_irqsave(&dev->lock, flags);

        count = readl(dev->base + PIPE_REG_GET_SIGNALLED);
        if (count == 0) {
                spin_unlock_irqrestore(&dev->lock, flags);
                return IRQ_NONE;
        }
        if (count > MAX_SIGNALLED_PIPES)
                count = MAX_SIGNALLED_PIPES;

        for (i = 0; i < count; ++i)
                signalled_pipes_add_locked(dev,
                        dev->buffers->signalled_pipe_buffers[i].id,
                        dev->buffers->signalled_pipe_buffers[i].flags);

        spin_unlock_irqrestore(&dev->lock, flags);

        tasklet_schedule(&goldfish_interrupt_tasklet);
        return IRQ_HANDLED;
}

static int get_free_pipe_id_locked(struct goldfish_pipe_dev *dev)
{
        int id;

        for (id = 0; id < dev->pipes_capacity; ++id)
                if (!dev->pipes[id])
                        return id;

        {
                /* Reallocate the array */
                u32 new_capacity = 2 * dev->pipes_capacity;
                struct goldfish_pipe **pipes =
                        kcalloc(new_capacity, sizeof(*pipes), GFP_ATOMIC);
                if (!pipes)
                        return -ENOMEM;
                memcpy(pipes, dev->pipes, sizeof(*pipes) * dev->pipes_capacity);
                kfree(dev->pipes);
                dev->pipes = pipes;
                id = dev->pipes_capacity;
                dev->pipes_capacity = new_capacity;
        }
        return id;
}

/**
 *      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_dev *dev = pipe_dev;
        unsigned long flags;
        int id;
        int status;

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

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

        /*
         * Command buffer needs to be allocated on its own page to make sure
         * it is physically contiguous in host's address space.
         */
        pipe->command_buffer =
                (struct goldfish_pipe_command *)__get_free_page(GFP_KERNEL);
        if (!pipe->command_buffer) {
                status = -ENOMEM;
                goto err_pipe;
        }

        spin_lock_irqsave(&dev->lock, flags);

        id = get_free_pipe_id_locked(dev);
        if (id < 0) {
                status = id;
                goto err_id_locked;
        }

        dev->pipes[id] = pipe;
        pipe->id = id;
        pipe->command_buffer->id = id;

        /* Now tell the emulator we're opening a new pipe. */
        dev->buffers->open_command_params.rw_params_max_count =
                        MAX_BUFFERS_PER_COMMAND;
        dev->buffers->open_command_params.command_buffer_ptr =
                        (u64)(unsigned long)__pa(pipe->command_buffer);
        status = goldfish_cmd_locked(pipe, PIPE_CMD_OPEN);
        spin_unlock_irqrestore(&dev->lock, flags);
        if (status < 0)
                goto err_cmd;
        /* All is done, save the pipe into the file's private data field */
        file->private_data = pipe;
        return 0;

err_cmd:
        spin_lock_irqsave(&dev->lock, flags);
        dev->pipes[id] = NULL;
err_id_locked:
        spin_unlock_irqrestore(&dev->lock, flags);
        free_page((unsigned long)pipe->command_buffer);
err_pipe:
        kfree(pipe);
        return status;
}

static int goldfish_pipe_release(struct inode *inode, struct file *filp)
{
        unsigned long flags;
        struct goldfish_pipe *pipe = filp->private_data;
        struct goldfish_pipe_dev *dev = pipe->dev;

        /* The guest is closing the channel, so tell the emulator right now */
        (void)goldfish_cmd(pipe, PIPE_CMD_CLOSE);

        spin_lock_irqsave(&dev->lock, flags);
        dev->pipes[pipe->id] = NULL;
        signalled_pipes_remove_locked(dev, pipe);
        spin_unlock_irqrestore(&dev->lock, flags);

        filp->private_data = NULL;
        free_page((unsigned long)pipe->command_buffer);
        kfree(pipe);
        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_dev = {
        .minor = MISC_DYNAMIC_MINOR,
        .name = "goldfish_pipe",
        .fops = &goldfish_pipe_fops,
};

static int goldfish_pipe_device_init(struct platform_device *pdev)
{
        char *page;
        struct goldfish_pipe_dev *dev = pipe_dev;
        int 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 for v2\n");
                return err;
        }

        err = misc_register(&goldfish_pipe_dev);
        if (err) {
                dev_err(&pdev->dev, "unable to register v2 device\n");
                return err;
        }

        dev->first_signalled_pipe = NULL;
        dev->pipes_capacity = INITIAL_PIPES_CAPACITY;
        dev->pipes = kcalloc(dev->pipes_capacity, sizeof(*dev->pipes),
                                        GFP_KERNEL);
        if (!dev->pipes)
                return -ENOMEM;

        /*
         * We're going to pass two buffers, open_command_params and
         * signalled_pipe_buffers, to the host. This means each of those buffers
         * needs to be contained in a single physical page. The easiest choice
         * is to just allocate a page and place the buffers in it.
         */
        if (WARN_ON(sizeof(*dev->buffers) > PAGE_SIZE))
                return -ENOMEM;

        page = (char *)__get_free_page(GFP_KERNEL);
        if (!page) {
                kfree(dev->pipes);
                return -ENOMEM;
        }
        dev->buffers = (struct goldfish_pipe_dev_buffers *)page;

        /* Send the buffer addresses to the host */
        {
                u64 paddr = __pa(&dev->buffers->signalled_pipe_buffers);

                writel((u32)(unsigned long)(paddr >> 32),
                        dev->base + PIPE_REG_SIGNAL_BUFFER_HIGH);
                writel((u32)(unsigned long)paddr,
                        dev->base + PIPE_REG_SIGNAL_BUFFER);
                writel((u32)MAX_SIGNALLED_PIPES,
                        dev->base + PIPE_REG_SIGNAL_BUFFER_COUNT);

                paddr = __pa(&dev->buffers->open_command_params);
                writel((u32)(unsigned long)(paddr >> 32),
                        dev->base + PIPE_REG_OPEN_BUFFER_HIGH);
                writel((u32)(unsigned long)paddr,
                        dev->base + PIPE_REG_OPEN_BUFFER);
        }
        return 0;
}

static void goldfish_pipe_device_deinit(struct platform_device *pdev)
{
        struct goldfish_pipe_dev *dev = pipe_dev;

        misc_deregister(&goldfish_pipe_dev);
        kfree(dev->pipes);
        free_page((unsigned long)dev->buffers);
}

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

        if (WARN_ON(sizeof(struct goldfish_pipe_command) > PAGE_SIZE))
                return -ENOMEM;

        /* 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;

        /*
         * Exchange the versions with the host device
         *
         * Note: v1 driver used to not report its version, so we write it before
         *  reading device version back: this allows the host implementation to
         *  detect the old driver (if there was no version write before read).
         */
        writel((u32)PIPE_DRIVER_VERSION, dev->base + PIPE_REG_VERSION);
        dev->version = readl(dev->base + PIPE_REG_VERSION);
        if (WARN_ON(dev->version < PIPE_CURRENT_DEVICE_VERSION))
                return -EINVAL;

        err = goldfish_pipe_device_init(pdev);
        if (!err)
                return 0;

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

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

static const struct acpi_device_id goldfish_pipe_acpi_match[] = {
        { "GFSH0003", 0 },
        { },
};
MODULE_DEVICE_TABLE(acpi, goldfish_pipe_acpi_match);

static const struct of_device_id goldfish_pipe_of_match[] = {
        { .compatible = "google,android-pipe", },
        {},
};
MODULE_DEVICE_TABLE(of, goldfish_pipe_of_match);

static struct platform_driver goldfish_pipe_driver = {
        .probe = goldfish_pipe_probe,
        .remove = goldfish_pipe_remove,
        .driver = {
                .name = "goldfish_pipe",
                .of_match_table = goldfish_pipe_of_match,
                .acpi_match_table = ACPI_PTR(goldfish_pipe_acpi_match),
        }
};

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