hwmon: (acpi_power_meter) Fix acpi_bus_get_device() return value check

[linux-drm-fsl-dcu.git] / drivers / misc / carma / carma-fpga.c

/*
 * CARMA DATA-FPGA Access Driver
 *
 * Copyright (c) 2009-2011 Ira W. Snyder <iws@ovro.caltech.edu>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 */

/*
 * FPGA Memory Dump Format
 *
 * FPGA #0 control registers (32 x 32-bit words)
 * FPGA #1 control registers (32 x 32-bit words)
 * FPGA #2 control registers (32 x 32-bit words)
 * FPGA #3 control registers (32 x 32-bit words)
 * SYSFPGA control registers (32 x 32-bit words)
 * FPGA #0 correlation array (NUM_CORL0 correlation blocks)
 * FPGA #1 correlation array (NUM_CORL1 correlation blocks)
 * FPGA #2 correlation array (NUM_CORL2 correlation blocks)
 * FPGA #3 correlation array (NUM_CORL3 correlation blocks)
 *
 * Each correlation array consists of:
 *
 * Correlation Data      (2 x NUM_LAGSn x 32-bit words)
 * Pipeline Metadata     (2 x NUM_METAn x 32-bit words)
 * Quantization Counters (2 x NUM_QCNTn x 32-bit words)
 *
 * The NUM_CORLn, NUM_LAGSn, NUM_METAn, and NUM_QCNTn values come from
 * the FPGA configuration registers. They do not change once the FPGA's
 * have been programmed, they only change on re-programming.
 */

/*
 * Basic Description:
 *
 * This driver is used to capture correlation spectra off of the four data
 * processing FPGAs. The FPGAs are often reprogrammed at runtime, therefore
 * this driver supports dynamic enable/disable of capture while the device
 * remains open.
 *
 * The nominal capture rate is 64Hz (every 15.625ms). To facilitate this fast
 * capture rate, all buffers are pre-allocated to avoid any potentially long
 * running memory allocations while capturing.
 *
 * There are two lists and one pointer which are used to keep track of the
 * different states of data buffers.
 *
 * 1) free list
 * This list holds all empty data buffers which are ready to receive data.
 *
 * 2) inflight pointer
 * This pointer holds the currently inflight data buffer. This buffer is having
 * data copied into it by the DMA engine.
 *
 * 3) used list
 * This list holds data buffers which have been filled, and are waiting to be
 * read by userspace.
 *
 * All buffers start life on the free list, then move successively to the
 * inflight pointer, and then to the used list. After they have been read by
 * userspace, they are moved back to the free list. The cycle repeats as long
 * as necessary.
 *
 * It should be noted that all buffers are mapped and ready for DMA when they
 * are on any of the three lists. They are only unmapped when they are in the
 * process of being read by userspace.
 */

/*
 * Notes on the IRQ masking scheme:
 *
 * The IRQ masking scheme here is different than most other hardware. The only
 * way for the DATA-FPGAs to detect if the kernel has taken too long to copy
 * the data is if the status registers are not cleared before the next
 * correlation data dump is ready.
 *
 * The interrupt line is connected to the status registers, such that when they
 * are cleared, the interrupt is de-asserted. Therein lies our problem. We need
 * to schedule a long-running DMA operation and return from the interrupt
 * handler quickly, but we cannot clear the status registers.
 *
 * To handle this, the system controller FPGA has the capability to connect the
 * interrupt line to a user-controlled GPIO pin. This pin is driven high
 * (unasserted) and left that way. To mask the interrupt, we change the
 * interrupt source to the GPIO pin. Tada, we hid the interrupt. :)
 */

#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/of_platform.h>
#include <linux/dma-mapping.h>
#include <linux/miscdevice.h>
#include <linux/interrupt.h>
#include <linux/dmaengine.h>
#include <linux/seq_file.h>
#include <linux/highmem.h>
#include <linux/debugfs.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/kref.h>
#include <linux/io.h>

#include <media/videobuf-dma-sg.h>

/* system controller registers */
#define SYS_IRQ_SOURCE_CTL      0x24
#define SYS_IRQ_OUTPUT_EN       0x28
#define SYS_IRQ_OUTPUT_DATA     0x2C
#define SYS_IRQ_INPUT_DATA      0x30
#define SYS_FPGA_CONFIG_STATUS  0x44

/* GPIO IRQ line assignment */
#define IRQ_CORL_DONE           0x10

/* FPGA registers */
#define MMAP_REG_VERSION        0x00
#define MMAP_REG_CORL_CONF1     0x08
#define MMAP_REG_CORL_CONF2     0x0C
#define MMAP_REG_STATUS         0x48

#define SYS_FPGA_BLOCK          0xF0000000

#define DATA_FPGA_START         0x400000
#define DATA_FPGA_SIZE          0x80000

static const char drv_name[] = "carma-fpga";

#define NUM_FPGA        4

#define MIN_DATA_BUFS   8
#define MAX_DATA_BUFS   64

struct fpga_info {
        unsigned int num_lag_ram;
        unsigned int blk_size;
};

struct data_buf {
        struct list_head entry;
        struct videobuf_dmabuf vb;
        size_t size;
};

struct fpga_device {
        /* character device */
        struct miscdevice miscdev;
        struct device *dev;
        struct mutex mutex;

        /* reference count */
        struct kref ref;

        /* FPGA registers and information */
        struct fpga_info info[NUM_FPGA];
        void __iomem *regs;
        int irq;

        /* FPGA Physical Address/Size Information */
        resource_size_t phys_addr;
        size_t phys_size;

        /* DMA structures */
        struct sg_table corl_table;
        unsigned int corl_nents;
        struct dma_chan *chan;

        /* Protection for all members below */
        spinlock_t lock;

        /* Device enable/disable flag */
        bool enabled;

        /* Correlation data buffers */
        wait_queue_head_t wait;
        struct list_head free;
        struct list_head used;
        struct data_buf *inflight;

        /* Information about data buffers */
        unsigned int num_dropped;
        unsigned int num_buffers;
        size_t bufsize;
        struct dentry *dbg_entry;
};

struct fpga_reader {
        struct fpga_device *priv;
        struct data_buf *buf;
        off_t buf_start;
};

static void fpga_device_release(struct kref *ref)
{
        struct fpga_device *priv = container_of(ref, struct fpga_device, ref);

        /* the last reader has exited, cleanup the last bits */
        mutex_destroy(&priv->mutex);
        kfree(priv);
}

/*
 * Data Buffer Allocation Helpers
 */

/**
 * data_free_buffer() - free a single data buffer and all allocated memory
 * @buf: the buffer to free
 *
 * This will free all of the pages allocated to the given data buffer, and
 * then free the structure itself
 */
static void data_free_buffer(struct data_buf *buf)
{
        /* It is ok to free a NULL buffer */
        if (!buf)
                return;

        /* free all memory */
        videobuf_dma_free(&buf->vb);
        kfree(buf);
}

/**
 * data_alloc_buffer() - allocate and fill a data buffer with pages
 * @bytes: the number of bytes required
 *
 * This allocates all space needed for a data buffer. It must be mapped before
 * use in a DMA transaction using videobuf_dma_map().
 *
 * Returns NULL on failure
 */
static struct data_buf *data_alloc_buffer(const size_t bytes)
{
        unsigned int nr_pages;
        struct data_buf *buf;
        int ret;

        /* calculate the number of pages necessary */
        nr_pages = DIV_ROUND_UP(bytes, PAGE_SIZE);

        /* allocate the buffer structure */
        buf = kzalloc(sizeof(*buf), GFP_KERNEL);
        if (!buf)
                goto out_return;

        /* initialize internal fields */
        INIT_LIST_HEAD(&buf->entry);
        buf->size = bytes;

        /* allocate the videobuf */
        videobuf_dma_init(&buf->vb);
        ret = videobuf_dma_init_kernel(&buf->vb, DMA_FROM_DEVICE, nr_pages);
        if (ret)
                goto out_free_buf;

        return buf;

out_free_buf:
        kfree(buf);
out_return:
        return NULL;
}

/**
 * data_free_buffers() - free all allocated buffers
 * @priv: the driver's private data structure
 *
 * Free all buffers allocated by the driver (except those currently in the
 * process of being read by userspace).
 *
 * LOCKING: must hold dev->mutex
 * CONTEXT: user
 */
static void data_free_buffers(struct fpga_device *priv)
{
        struct data_buf *buf, *tmp;

        /* the device should be stopped, no DMA in progress */
        BUG_ON(priv->inflight != NULL);

        list_for_each_entry_safe(buf, tmp, &priv->free, entry) {
                list_del_init(&buf->entry);
                videobuf_dma_unmap(priv->dev, &buf->vb);
                data_free_buffer(buf);
        }

        list_for_each_entry_safe(buf, tmp, &priv->used, entry) {
                list_del_init(&buf->entry);
                videobuf_dma_unmap(priv->dev, &buf->vb);
                data_free_buffer(buf);
        }

        priv->num_buffers = 0;
        priv->bufsize = 0;
}

/**
 * data_alloc_buffers() - allocate 1 seconds worth of data buffers
 * @priv: the driver's private data structure
 *
 * Allocate enough buffers for a whole second worth of data
 *
 * This routine will attempt to degrade nicely by succeeding even if a full
 * second worth of data buffers could not be allocated, as long as a minimum
 * number were allocated. In this case, it will print a message to the kernel
 * log.
 *
 * The device must not be modifying any lists when this is called.
 *
 * CONTEXT: user
 * LOCKING: must hold dev->mutex
 *
 * Returns 0 on success, -ERRNO otherwise
 */
static int data_alloc_buffers(struct fpga_device *priv)
{
        struct data_buf *buf;
        int i, ret;

        for (i = 0; i < MAX_DATA_BUFS; i++) {

                /* allocate a buffer */
                buf = data_alloc_buffer(priv->bufsize);
                if (!buf)
                        break;

                /* map it for DMA */
                ret = videobuf_dma_map(priv->dev, &buf->vb);
                if (ret) {
                        data_free_buffer(buf);
                        break;
                }

                /* add it to the list of free buffers */
                list_add_tail(&buf->entry, &priv->free);
                priv->num_buffers++;
        }

        /* Make sure we allocated the minimum required number of buffers */
        if (priv->num_buffers < MIN_DATA_BUFS) {
                dev_err(priv->dev, "Unable to allocate enough data buffers\n");
                data_free_buffers(priv);
                return -ENOMEM;
        }

        /* Warn if we are running in a degraded state, but do not fail */
        if (priv->num_buffers < MAX_DATA_BUFS) {
                dev_warn(priv->dev,
                         "Unable to allocate %d buffers, using %d buffers instead\n",
                         MAX_DATA_BUFS, i);
        }

        return 0;
}

/*
 * DMA Operations Helpers
 */

/**
 * fpga_start_addr() - get the physical address a DATA-FPGA
 * @priv: the driver's private data structure
 * @fpga: the DATA-FPGA number (zero based)
 */
static dma_addr_t fpga_start_addr(struct fpga_device *priv, unsigned int fpga)
{
        return priv->phys_addr + 0x400000 + (0x80000 * fpga);
}

/**
 * fpga_block_addr() - get the physical address of a correlation data block
 * @priv: the driver's private data structure
 * @fpga: the DATA-FPGA number (zero based)
 * @blknum: the correlation block number (zero based)
 */
static dma_addr_t fpga_block_addr(struct fpga_device *priv, unsigned int fpga,
                                  unsigned int blknum)
{
        return fpga_start_addr(priv, fpga) + (0x10000 * (1 + blknum));
}

#define REG_BLOCK_SIZE  (32 * 4)

/**
 * data_setup_corl_table() - create the scatterlist for correlation dumps
 * @priv: the driver's private data structure
 *
 * Create the scatterlist for transferring a correlation dump from the
 * DATA FPGAs. This structure will be reused for each buffer than needs
 * to be filled with correlation data.
 *
 * Returns 0 on success, -ERRNO otherwise
 */
static int data_setup_corl_table(struct fpga_device *priv)
{
        struct sg_table *table = &priv->corl_table;
        struct scatterlist *sg;
        struct fpga_info *info;
        int i, j, ret;

        /* Calculate the number of entries needed */
        priv->corl_nents = (1 + NUM_FPGA) * REG_BLOCK_SIZE;
        for (i = 0; i < NUM_FPGA; i++)
                priv->corl_nents += priv->info[i].num_lag_ram;

        /* Allocate the scatterlist table */
        ret = sg_alloc_table(table, priv->corl_nents, GFP_KERNEL);
        if (ret) {
                dev_err(priv->dev, "unable to allocate DMA table\n");
                return ret;
        }

        /* Add the DATA FPGA registers to the scatterlist */
        sg = table->sgl;
        for (i = 0; i < NUM_FPGA; i++) {
                sg_dma_address(sg) = fpga_start_addr(priv, i);
                sg_dma_len(sg) = REG_BLOCK_SIZE;
                sg = sg_next(sg);
        }

        /* Add the SYS-FPGA registers to the scatterlist */
        sg_dma_address(sg) = SYS_FPGA_BLOCK;
        sg_dma_len(sg) = REG_BLOCK_SIZE;
        sg = sg_next(sg);

        /* Add the FPGA correlation data blocks to the scatterlist */
        for (i = 0; i < NUM_FPGA; i++) {
                info = &priv->info[i];
                for (j = 0; j < info->num_lag_ram; j++) {
                        sg_dma_address(sg) = fpga_block_addr(priv, i, j);
                        sg_dma_len(sg) = info->blk_size;
                        sg = sg_next(sg);
                }
        }

        /*
         * All physical addresses and lengths are present in the structure
         * now. It can be reused for every FPGA DATA interrupt
         */
        return 0;
}

/*
 * FPGA Register Access Helpers
 */

static void fpga_write_reg(struct fpga_device *priv, unsigned int fpga,
                           unsigned int reg, u32 val)
{
        const int fpga_start = DATA_FPGA_START + (fpga * DATA_FPGA_SIZE);
        iowrite32be(val, priv->regs + fpga_start + reg);
}

static u32 fpga_read_reg(struct fpga_device *priv, unsigned int fpga,
                         unsigned int reg)
{
        const int fpga_start = DATA_FPGA_START + (fpga * DATA_FPGA_SIZE);
        return ioread32be(priv->regs + fpga_start + reg);
}

/**
 * data_calculate_bufsize() - calculate the data buffer size required
 * @priv: the driver's private data structure
 *
 * Calculate the total buffer size needed to hold a single block
 * of correlation data
 *
 * CONTEXT: user
 *
 * Returns 0 on success, -ERRNO otherwise
 */
static int data_calculate_bufsize(struct fpga_device *priv)
{
        u32 num_corl, num_lags, num_meta, num_qcnt, num_pack;
        u32 conf1, conf2, version;
        u32 num_lag_ram, blk_size;
        int i;

        /* Each buffer starts with the 5 FPGA register areas */
        priv->bufsize = (1 + NUM_FPGA) * REG_BLOCK_SIZE;

        /* Read and store the configuration data for each FPGA */
        for (i = 0; i < NUM_FPGA; i++) {
                version = fpga_read_reg(priv, i, MMAP_REG_VERSION);
                conf1 = fpga_read_reg(priv, i, MMAP_REG_CORL_CONF1);
                conf2 = fpga_read_reg(priv, i, MMAP_REG_CORL_CONF2);

                /* minor version 2 and later */
                if ((version & 0x000000FF) >= 2) {
                        num_corl = (conf1 & 0x000000F0) >> 4;
                        num_pack = (conf1 & 0x00000F00) >> 8;
                        num_lags = (conf1 & 0x00FFF000) >> 12;
                        num_meta = (conf1 & 0x7F000000) >> 24;
                        num_qcnt = (conf2 & 0x00000FFF) >> 0;
                } else {
                        num_corl = (conf1 & 0x000000F0) >> 4;
                        num_pack = 1; /* implied */
                        num_lags = (conf1 & 0x000FFF00) >> 8;
                        num_meta = (conf1 & 0x7FF00000) >> 20;
                        num_qcnt = (conf2 & 0x00000FFF) >> 0;
                }

                num_lag_ram = (num_corl + num_pack - 1) / num_pack;
                blk_size = ((num_pack * num_lags) + num_meta + num_qcnt) * 8;

                priv->info[i].num_lag_ram = num_lag_ram;
                priv->info[i].blk_size = blk_size;
                priv->bufsize += num_lag_ram * blk_size;

                dev_dbg(priv->dev, "FPGA %d NUM_CORL: %d\n", i, num_corl);
                dev_dbg(priv->dev, "FPGA %d NUM_PACK: %d\n", i, num_pack);
                dev_dbg(priv->dev, "FPGA %d NUM_LAGS: %d\n", i, num_lags);
                dev_dbg(priv->dev, "FPGA %d NUM_META: %d\n", i, num_meta);
                dev_dbg(priv->dev, "FPGA %d NUM_QCNT: %d\n", i, num_qcnt);
                dev_dbg(priv->dev, "FPGA %d BLK_SIZE: %d\n", i, blk_size);
        }

        dev_dbg(priv->dev, "TOTAL BUFFER SIZE: %zu bytes\n", priv->bufsize);
        return 0;
}

/*
 * Interrupt Handling
 */

/**
 * data_disable_interrupts() - stop the device from generating interrupts
 * @priv: the driver's private data structure
 *
 * Hide interrupts by switching to GPIO interrupt source
 *
 * LOCKING: must hold dev->lock
 */
static void data_disable_interrupts(struct fpga_device *priv)
{
        /* hide the interrupt by switching the IRQ driver to GPIO */
        iowrite32be(0x2F, priv->regs + SYS_IRQ_SOURCE_CTL);
}

/**
 * data_enable_interrupts() - allow the device to generate interrupts
 * @priv: the driver's private data structure
 *
 * Unhide interrupts by switching to the FPGA interrupt source. At the
 * same time, clear the DATA-FPGA status registers.
 *
 * LOCKING: must hold dev->lock
 */
static void data_enable_interrupts(struct fpga_device *priv)
{
        /* clear the actual FPGA corl_done interrupt */
        fpga_write_reg(priv, 0, MMAP_REG_STATUS, 0x0);
        fpga_write_reg(priv, 1, MMAP_REG_STATUS, 0x0);
        fpga_write_reg(priv, 2, MMAP_REG_STATUS, 0x0);
        fpga_write_reg(priv, 3, MMAP_REG_STATUS, 0x0);

        /* flush the writes */
        fpga_read_reg(priv, 0, MMAP_REG_STATUS);
        fpga_read_reg(priv, 1, MMAP_REG_STATUS);
        fpga_read_reg(priv, 2, MMAP_REG_STATUS);
        fpga_read_reg(priv, 3, MMAP_REG_STATUS);

        /* switch back to the external interrupt source */
        iowrite32be(0x3F, priv->regs + SYS_IRQ_SOURCE_CTL);
}

/**
 * data_dma_cb() - DMAEngine callback for DMA completion
 * @data: the driver's private data structure
 *
 * Complete a DMA transfer from the DATA-FPGA's
 *
 * This is called via the DMA callback mechanism, and will handle moving the
 * completed DMA transaction to the used list, and then wake any processes
 * waiting for new data
 *
 * CONTEXT: any, softirq expected
 */
static void data_dma_cb(void *data)
{
        struct fpga_device *priv = data;
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);

        /* If there is no inflight buffer, we've got a bug */
        BUG_ON(priv->inflight == NULL);

        /* Move the inflight buffer onto the used list */
        list_move_tail(&priv->inflight->entry, &priv->used);
        priv->inflight = NULL;

        /*
         * If data dumping is still enabled, then clear the FPGA
         * status registers and re-enable FPGA interrupts
         */
        if (priv->enabled)
                data_enable_interrupts(priv);

        spin_unlock_irqrestore(&priv->lock, flags);

        /*
         * We've changed both the inflight and used lists, so we need
         * to wake up any processes that are blocking for those events
         */
        wake_up(&priv->wait);
}

/**
 * data_submit_dma() - prepare and submit the required DMA to fill a buffer
 * @priv: the driver's private data structure
 * @buf: the data buffer
 *
 * Prepare and submit the necessary DMA transactions to fill a correlation
 * data buffer.
 *
 * LOCKING: must hold dev->lock
 * CONTEXT: hardirq only
 *
 * Returns 0 on success, -ERRNO otherwise
 */
static int data_submit_dma(struct fpga_device *priv, struct data_buf *buf)
{
        struct scatterlist *dst_sg, *src_sg;
        unsigned int dst_nents, src_nents;
        struct dma_chan *chan = priv->chan;
        struct dma_async_tx_descriptor *tx;
        dma_cookie_t cookie;
        dma_addr_t dst, src;
        unsigned long dma_flags = DMA_COMPL_SKIP_DEST_UNMAP |
                                  DMA_COMPL_SKIP_SRC_UNMAP;

        dst_sg = buf->vb.sglist;
        dst_nents = buf->vb.sglen;

        src_sg = priv->corl_table.sgl;
        src_nents = priv->corl_nents;

        /*
         * All buffers passed to this function should be ready and mapped
         * for DMA already. Therefore, we don't need to do anything except
         * submit it to the Freescale DMA Engine for processing
         */

        /* setup the scatterlist to scatterlist transfer */
        tx = chan->device->device_prep_dma_sg(chan,
                                              dst_sg, dst_nents,
                                              src_sg, src_nents,
                                              0);
        if (!tx) {
                dev_err(priv->dev, "unable to prep scatterlist DMA\n");
                return -ENOMEM;
        }

        /* submit the transaction to the DMA controller */
        cookie = tx->tx_submit(tx);
        if (dma_submit_error(cookie)) {
                dev_err(priv->dev, "unable to submit scatterlist DMA\n");
                return -ENOMEM;
        }

        /* Prepare the re-read of the SYS-FPGA block */
        dst = sg_dma_address(dst_sg) + (NUM_FPGA * REG_BLOCK_SIZE);
        src = SYS_FPGA_BLOCK;
        tx = chan->device->device_prep_dma_memcpy(chan, dst, src,
                                                  REG_BLOCK_SIZE,
                                                  dma_flags);
        if (!tx) {
                dev_err(priv->dev, "unable to prep SYS-FPGA DMA\n");
                return -ENOMEM;
        }

        /* Setup the callback */
        tx->callback = data_dma_cb;
        tx->callback_param = priv;

        /* submit the transaction to the DMA controller */
        cookie = tx->tx_submit(tx);
        if (dma_submit_error(cookie)) {
                dev_err(priv->dev, "unable to submit SYS-FPGA DMA\n");
                return -ENOMEM;
        }

        return 0;
}

#define CORL_DONE       0x1
#define CORL_ERR        0x2

static irqreturn_t data_irq(int irq, void *dev_id)
{
        struct fpga_device *priv = dev_id;
        bool submitted = false;
        struct data_buf *buf;
        u32 status;
        int i;

        /* detect spurious interrupts via FPGA status */
        for (i = 0; i < 4; i++) {
                status = fpga_read_reg(priv, i, MMAP_REG_STATUS);
                if (!(status & (CORL_DONE | CORL_ERR))) {
                        dev_err(priv->dev, "spurious irq detected (FPGA)\n");
                        return IRQ_NONE;
                }
        }

        /* detect spurious interrupts via raw IRQ pin readback */
        status = ioread32be(priv->regs + SYS_IRQ_INPUT_DATA);
        if (status & IRQ_CORL_DONE) {
                dev_err(priv->dev, "spurious irq detected (IRQ)\n");
                return IRQ_NONE;
        }

        spin_lock(&priv->lock);

        /*
         * This is an error case that should never happen.
         *
         * If this driver has a bug and manages to re-enable interrupts while
         * a DMA is in progress, then we will hit this statement and should
         * start paying attention immediately.
         */
        BUG_ON(priv->inflight != NULL);

        /* hide the interrupt by switching the IRQ driver to GPIO */
        data_disable_interrupts(priv);

        /* If there are no free buffers, drop this data */
        if (list_empty(&priv->free)) {
                priv->num_dropped++;
                goto out;
        }

        buf = list_first_entry(&priv->free, struct data_buf, entry);
        list_del_init(&buf->entry);
        BUG_ON(buf->size != priv->bufsize);

        /* Submit a DMA transfer to get the correlation data */
        if (data_submit_dma(priv, buf)) {
                dev_err(priv->dev, "Unable to setup DMA transfer\n");
                list_move_tail(&buf->entry, &priv->free);
                goto out;
        }

        /* Save the buffer for the DMA callback */
        priv->inflight = buf;
        submitted = true;

        /* Start the DMA Engine */
        dma_async_issue_pending(priv->chan);

out:
        /* If no DMA was submitted, re-enable interrupts */
        if (!submitted)
                data_enable_interrupts(priv);

        spin_unlock(&priv->lock);
        return IRQ_HANDLED;
}

/*
 * Realtime Device Enable Helpers
 */

/**
 * data_device_enable() - enable the device for buffered dumping
 * @priv: the driver's private data structure
 *
 * Enable the device for buffered dumping. Allocates buffers and hooks up
 * the interrupt handler. When this finishes, data will come pouring in.
 *
 * LOCKING: must hold dev->mutex
 * CONTEXT: user context only
 *
 * Returns 0 on success, -ERRNO otherwise
 */
static int data_device_enable(struct fpga_device *priv)
{
        bool enabled;
        u32 val;
        int ret;

        /* multiple enables are safe: they do nothing */
        spin_lock_irq(&priv->lock);
        enabled = priv->enabled;
        spin_unlock_irq(&priv->lock);
        if (enabled)
                return 0;

        /* check that the FPGAs are programmed */
        val = ioread32be(priv->regs + SYS_FPGA_CONFIG_STATUS);
        if (!(val & (1 << 18))) {
                dev_err(priv->dev, "DATA-FPGAs are not enabled\n");
                return -ENODATA;
        }

        /* read the FPGAs to calculate the buffer size */
        ret = data_calculate_bufsize(priv);
        if (ret) {
                dev_err(priv->dev, "unable to calculate buffer size\n");
                goto out_error;
        }

        /* allocate the correlation data buffers */
        ret = data_alloc_buffers(priv);
        if (ret) {
                dev_err(priv->dev, "unable to allocate buffers\n");
                goto out_error;
        }

        /* setup the source scatterlist for dumping correlation data */
        ret = data_setup_corl_table(priv);
        if (ret) {
                dev_err(priv->dev, "unable to setup correlation DMA table\n");
                goto out_error;
        }

        /* prevent the FPGAs from generating interrupts */
        data_disable_interrupts(priv);

        /* hookup the irq handler */
        ret = request_irq(priv->irq, data_irq, IRQF_SHARED, drv_name, priv);
        if (ret) {
                dev_err(priv->dev, "unable to request IRQ handler\n");
                goto out_error;
        }

        /* allow the DMA callback to re-enable FPGA interrupts */
        spin_lock_irq(&priv->lock);
        priv->enabled = true;
        spin_unlock_irq(&priv->lock);

        /* allow the FPGAs to generate interrupts */
        data_enable_interrupts(priv);
        return 0;

out_error:
        sg_free_table(&priv->corl_table);
        priv->corl_nents = 0;

        data_free_buffers(priv);
        return ret;
}

/**
 * data_device_disable() - disable the device for buffered dumping
 * @priv: the driver's private data structure
 *
 * Disable the device for buffered dumping. Stops new DMA transactions from
 * being generated, waits for all outstanding DMA to complete, and then frees
 * all buffers.
 *
 * LOCKING: must hold dev->mutex
 * CONTEXT: user only
 *
 * Returns 0 on success, -ERRNO otherwise
 */
static int data_device_disable(struct fpga_device *priv)
{
        spin_lock_irq(&priv->lock);

        /* allow multiple disable */
        if (!priv->enabled) {
                spin_unlock_irq(&priv->lock);
                return 0;
        }

        /*
         * Mark the device disabled
         *
         * This stops DMA callbacks from re-enabling interrupts
         */
        priv->enabled = false;

        /* prevent the FPGAs from generating interrupts */
        data_disable_interrupts(priv);

        /* wait until all ongoing DMA has finished */
        while (priv->inflight != NULL) {
                spin_unlock_irq(&priv->lock);
                wait_event(priv->wait, priv->inflight == NULL);
                spin_lock_irq(&priv->lock);
        }

        spin_unlock_irq(&priv->lock);

        /* unhook the irq handler */
        free_irq(priv->irq, priv);

        /* free the correlation table */
        sg_free_table(&priv->corl_table);
        priv->corl_nents = 0;

        /* free all buffers: the free and used lists are not being changed */
        data_free_buffers(priv);
        return 0;
}

/*
 * DEBUGFS Interface
 */
#ifdef CONFIG_DEBUG_FS

/*
 * Count the number of entries in the given list
 */
static unsigned int list_num_entries(struct list_head *list)
{
        struct list_head *entry;
        unsigned int ret = 0;

        list_for_each(entry, list)
                ret++;

        return ret;
}

static int data_debug_show(struct seq_file *f, void *offset)
{
        struct fpga_device *priv = f->private;

        spin_lock_irq(&priv->lock);

        seq_printf(f, "enabled: %d\n", priv->enabled);
        seq_printf(f, "bufsize: %d\n", priv->bufsize);
        seq_printf(f, "num_buffers: %d\n", priv->num_buffers);
        seq_printf(f, "num_free: %d\n", list_num_entries(&priv->free));
        seq_printf(f, "inflight: %d\n", priv->inflight != NULL);
        seq_printf(f, "num_used: %d\n", list_num_entries(&priv->used));
        seq_printf(f, "num_dropped: %d\n", priv->num_dropped);

        spin_unlock_irq(&priv->lock);
        return 0;
}

static int data_debug_open(struct inode *inode, struct file *file)
{
        return single_open(file, data_debug_show, inode->i_private);
}

static const struct file_operations data_debug_fops = {
        .owner          = THIS_MODULE,
        .open           = data_debug_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static int data_debugfs_init(struct fpga_device *priv)
{
        priv->dbg_entry = debugfs_create_file(drv_name, S_IRUGO, NULL, priv,
                                              &data_debug_fops);
        if (IS_ERR(priv->dbg_entry))
                return PTR_ERR(priv->dbg_entry);

        return 0;
}

static void data_debugfs_exit(struct fpga_device *priv)
{
        debugfs_remove(priv->dbg_entry);
}

#else

static inline int data_debugfs_init(struct fpga_device *priv)
{
        return 0;
}

static inline void data_debugfs_exit(struct fpga_device *priv)
{
}

#endif  /* CONFIG_DEBUG_FS */

/*
 * SYSFS Attributes
 */

static ssize_t data_en_show(struct device *dev, struct device_attribute *attr,
                            char *buf)
{
        struct fpga_device *priv = dev_get_drvdata(dev);
        int ret;

        spin_lock_irq(&priv->lock);
        ret = snprintf(buf, PAGE_SIZE, "%u\n", priv->enabled);
        spin_unlock_irq(&priv->lock);

        return ret;
}

static ssize_t data_en_set(struct device *dev, struct device_attribute *attr,
                           const char *buf, size_t count)
{
        struct fpga_device *priv = dev_get_drvdata(dev);
        unsigned long enable;
        int ret;

        ret = kstrtoul(buf, 0, &enable);
        if (ret) {
                dev_err(priv->dev, "unable to parse enable input\n");
                return ret;
        }

        /* protect against concurrent enable/disable */
        ret = mutex_lock_interruptible(&priv->mutex);
        if (ret)
                return ret;

        if (enable)
                ret = data_device_enable(priv);
        else
                ret = data_device_disable(priv);

        if (ret) {
                dev_err(priv->dev, "device %s failed\n",
                        enable ? "enable" : "disable");
                count = ret;
                goto out_unlock;
        }

out_unlock:
        mutex_unlock(&priv->mutex);
        return count;
}

static DEVICE_ATTR(enable, S_IWUSR | S_IRUGO, data_en_show, data_en_set);

static struct attribute *data_sysfs_attrs[] = {
        &dev_attr_enable.attr,
        NULL,
};

static const struct attribute_group rt_sysfs_attr_group = {
        .attrs = data_sysfs_attrs,
};

/*
 * FPGA Realtime Data Character Device
 */

static int data_open(struct inode *inode, struct file *filp)
{
        /*
         * The miscdevice layer puts our struct miscdevice into the
         * filp->private_data field. We use this to find our private
         * data and then overwrite it with our own private structure.
         */
        struct fpga_device *priv = container_of(filp->private_data,
                                                struct fpga_device, miscdev);
        struct fpga_reader *reader;
        int ret;

        /* allocate private data */
        reader = kzalloc(sizeof(*reader), GFP_KERNEL);
        if (!reader)
                return -ENOMEM;

        reader->priv = priv;
        reader->buf = NULL;

        filp->private_data = reader;
        ret = nonseekable_open(inode, filp);
        if (ret) {
                dev_err(priv->dev, "nonseekable-open failed\n");
                kfree(reader);
                return ret;
        }

        /*
         * success, increase the reference count of the private data structure
         * so that it doesn't disappear if the device is unbound
         */
        kref_get(&priv->ref);
        return 0;
}

static int data_release(struct inode *inode, struct file *filp)
{
        struct fpga_reader *reader = filp->private_data;
        struct fpga_device *priv = reader->priv;

        /* free the per-reader structure */
        data_free_buffer(reader->buf);
        kfree(reader);
        filp->private_data = NULL;

        /* decrement our reference count to the private data */
        kref_put(&priv->ref, fpga_device_release);
        return 0;
}

static ssize_t data_read(struct file *filp, char __user *ubuf, size_t count,
                         loff_t *f_pos)
{
        struct fpga_reader *reader = filp->private_data;
        struct fpga_device *priv = reader->priv;
        struct list_head *used = &priv->used;
        bool drop_buffer = false;
        struct data_buf *dbuf;
        size_t avail;
        void *data;
        int ret;

        /* check if we already have a partial buffer */
        if (reader->buf) {
                dbuf = reader->buf;
                goto have_buffer;
        }

        spin_lock_irq(&priv->lock);

        /* Block until there is at least one buffer on the used list */
        while (list_empty(used)) {
                spin_unlock_irq(&priv->lock);

                if (filp->f_flags & O_NONBLOCK)
                        return -EAGAIN;

                ret = wait_event_interruptible(priv->wait, !list_empty(used));
                if (ret)
                        return ret;

                spin_lock_irq(&priv->lock);
        }

        /* Grab the first buffer off of the used list */
        dbuf = list_first_entry(used, struct data_buf, entry);
        list_del_init(&dbuf->entry);

        spin_unlock_irq(&priv->lock);

        /* Buffers are always mapped: unmap it */
        videobuf_dma_unmap(priv->dev, &dbuf->vb);

        /* save the buffer for later */
        reader->buf = dbuf;
        reader->buf_start = 0;

have_buffer:
        /* Get the number of bytes available */
        avail = dbuf->size - reader->buf_start;
        data = dbuf->vb.vaddr + reader->buf_start;

        /* Get the number of bytes we can transfer */
        count = min(count, avail);

        /* Copy the data to the userspace buffer */
        if (copy_to_user(ubuf, data, count))
                return -EFAULT;

        /* Update the amount of available space */
        avail -= count;

        /*
         * If there is still some data available, save the buffer for the
         * next userspace call to read() and return
         */
        if (avail > 0) {
                reader->buf_start += count;
                reader->buf = dbuf;
                return count;
        }

        /*
         * Get the buffer ready to be reused for DMA
         *
         * If it fails, we pretend that the read never happed and return
         * -EFAULT to userspace. The read will be retried.
         */
        ret = videobuf_dma_map(priv->dev, &dbuf->vb);
        if (ret) {
                dev_err(priv->dev, "unable to remap buffer for DMA\n");
                return -EFAULT;
        }

        /* Lock against concurrent enable/disable */
        spin_lock_irq(&priv->lock);

        /* the reader is finished with this buffer */
        reader->buf = NULL;

        /*
         * One of two things has happened, the device is disabled, or the
         * device has been reconfigured underneath us. In either case, we
         * should just throw away the buffer.
         *
         * Lockdep complains if this is done under the spinlock, so we
         * handle it during the unlock path.
         */
        if (!priv->enabled || dbuf->size != priv->bufsize) {
                drop_buffer = true;
                goto out_unlock;
        }

        /* The buffer is safe to reuse, so add it back to the free list */
        list_add_tail(&dbuf->entry, &priv->free);

out_unlock:
        spin_unlock_irq(&priv->lock);

        if (drop_buffer) {
                videobuf_dma_unmap(priv->dev, &dbuf->vb);
                data_free_buffer(dbuf);
        }

        return count;
}

static unsigned int data_poll(struct file *filp, struct poll_table_struct *tbl)
{
        struct fpga_reader *reader = filp->private_data;
        struct fpga_device *priv = reader->priv;
        unsigned int mask = 0;

        poll_wait(filp, &priv->wait, tbl);

        if (!list_empty(&priv->used))
                mask |= POLLIN | POLLRDNORM;

        return mask;
}

static int data_mmap(struct file *filp, struct vm_area_struct *vma)
{
        struct fpga_reader *reader = filp->private_data;
        struct fpga_device *priv = reader->priv;
        unsigned long offset, vsize, psize, addr;

        /* VMA properties */
        offset = vma->vm_pgoff << PAGE_SHIFT;
        vsize = vma->vm_end - vma->vm_start;
        psize = priv->phys_size - offset;
        addr = (priv->phys_addr + offset) >> PAGE_SHIFT;

        /* Check against the FPGA region's physical memory size */
        if (vsize > psize) {
                dev_err(priv->dev, "requested mmap mapping too large\n");
                return -EINVAL;
        }

        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);

        return io_remap_pfn_range(vma, vma->vm_start, addr, vsize,
                                  vma->vm_page_prot);
}

static const struct file_operations data_fops = {
        .owner          = THIS_MODULE,
        .open           = data_open,
        .release        = data_release,
        .read           = data_read,
        .poll           = data_poll,
        .mmap           = data_mmap,
        .llseek         = no_llseek,
};

/*
 * OpenFirmware Device Subsystem
 */

static bool dma_filter(struct dma_chan *chan, void *data)
{
        /*
         * DMA Channel #0 is used for the FPGA Programmer, so ignore it
         *
         * This probably won't survive an unload/load cycle of the Freescale
         * DMAEngine driver, but that won't be a problem
         */
        if (chan->chan_id == 0 && chan->device->dev_id == 0)
                return false;

        return true;
}

static int data_of_probe(struct platform_device *op)
{
        struct device_node *of_node = op->dev.of_node;
        struct device *this_device;
        struct fpga_device *priv;
        struct resource res;
        dma_cap_mask_t mask;
        int ret;

        /* Allocate private data */
        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (!priv) {
                dev_err(&op->dev, "Unable to allocate device private data\n");
                ret = -ENOMEM;
                goto out_return;
        }

        platform_set_drvdata(op, priv);
        priv->dev = &op->dev;
        kref_init(&priv->ref);
        mutex_init(&priv->mutex);

        dev_set_drvdata(priv->dev, priv);
        spin_lock_init(&priv->lock);
        INIT_LIST_HEAD(&priv->free);
        INIT_LIST_HEAD(&priv->used);
        init_waitqueue_head(&priv->wait);

        /* Setup the misc device */
        priv->miscdev.minor = MISC_DYNAMIC_MINOR;
        priv->miscdev.name = drv_name;
        priv->miscdev.fops = &data_fops;

        /* Get the physical address of the FPGA registers */
        ret = of_address_to_resource(of_node, 0, &res);
        if (ret) {
                dev_err(&op->dev, "Unable to find FPGA physical address\n");
                ret = -ENODEV;
                goto out_free_priv;
        }

        priv->phys_addr = res.start;
        priv->phys_size = resource_size(&res);

        /* ioremap the registers for use */
        priv->regs = of_iomap(of_node, 0);
        if (!priv->regs) {
                dev_err(&op->dev, "Unable to ioremap registers\n");
                ret = -ENOMEM;
                goto out_free_priv;
        }

        dma_cap_zero(mask);
        dma_cap_set(DMA_MEMCPY, mask);
        dma_cap_set(DMA_INTERRUPT, mask);
        dma_cap_set(DMA_SLAVE, mask);
        dma_cap_set(DMA_SG, mask);

        /* Request a DMA channel */
        priv->chan = dma_request_channel(mask, dma_filter, NULL);
        if (!priv->chan) {
                dev_err(&op->dev, "Unable to request DMA channel\n");
                ret = -ENODEV;
                goto out_unmap_regs;
        }

        /* Find the correct IRQ number */
        priv->irq = irq_of_parse_and_map(of_node, 0);
        if (priv->irq == NO_IRQ) {
                dev_err(&op->dev, "Unable to find IRQ line\n");
                ret = -ENODEV;
                goto out_release_dma;
        }

        /* Drive the GPIO for FPGA IRQ high (no interrupt) */
        iowrite32be(IRQ_CORL_DONE, priv->regs + SYS_IRQ_OUTPUT_DATA);

        /* Register the miscdevice */
        ret = misc_register(&priv->miscdev);
        if (ret) {
                dev_err(&op->dev, "Unable to register miscdevice\n");
                goto out_irq_dispose_mapping;
        }

        /* Create the debugfs files */
        ret = data_debugfs_init(priv);
        if (ret) {
                dev_err(&op->dev, "Unable to create debugfs files\n");
                goto out_misc_deregister;
        }

        /* Create the sysfs files */
        this_device = priv->miscdev.this_device;
        dev_set_drvdata(this_device, priv);
        ret = sysfs_create_group(&this_device->kobj, &rt_sysfs_attr_group);
        if (ret) {
                dev_err(&op->dev, "Unable to create sysfs files\n");
                goto out_data_debugfs_exit;
        }

        dev_info(&op->dev, "CARMA FPGA Realtime Data Driver Loaded\n");
        return 0;

out_data_debugfs_exit:
        data_debugfs_exit(priv);
out_misc_deregister:
        misc_deregister(&priv->miscdev);
out_irq_dispose_mapping:
        irq_dispose_mapping(priv->irq);
out_release_dma:
        dma_release_channel(priv->chan);
out_unmap_regs:
        iounmap(priv->regs);
out_free_priv:
        kref_put(&priv->ref, fpga_device_release);
out_return:
        return ret;
}

static int data_of_remove(struct platform_device *op)
{
        struct fpga_device *priv = platform_get_drvdata(op);
        struct device *this_device = priv->miscdev.this_device;

        /* remove all sysfs files, now the device cannot be re-enabled */
        sysfs_remove_group(&this_device->kobj, &rt_sysfs_attr_group);

        /* remove all debugfs files */
        data_debugfs_exit(priv);

        /* disable the device from generating data */
        data_device_disable(priv);

        /* remove the character device to stop new readers from appearing */
        misc_deregister(&priv->miscdev);

        /* cleanup everything not needed by readers */
        irq_dispose_mapping(priv->irq);
        dma_release_channel(priv->chan);
        iounmap(priv->regs);

        /* release our reference */
        kref_put(&priv->ref, fpga_device_release);
        return 0;
}

static struct of_device_id data_of_match[] = {
        { .compatible = "carma,carma-fpga", },
        {},
};

static struct platform_driver data_of_driver = {
        .probe          = data_of_probe,
        .remove         = data_of_remove,
        .driver         = {
                .name           = drv_name,
                .of_match_table = data_of_match,
                .owner          = THIS_MODULE,
        },
};

module_platform_driver(data_of_driver);

MODULE_AUTHOR("Ira W. Snyder <iws@ovro.caltech.edu>");
MODULE_DESCRIPTION("CARMA DATA-FPGA Access Driver");
MODULE_LICENSE("GPL");