linux/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_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);

	/* 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;

	/* clear the FPGA status and re-enable interrupts */
	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;

	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_PREP_INTERRUPT);
	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);

	/* 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_memcpy_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)
{
	u32 val;
	int ret;

	/* multiple enables are safe: they do nothing */
	if (priv->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;
	}

	/* 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;
	}

	/* switch to the external FPGA IRQ line */
	data_enable_interrupts(priv);

	/* success, we're enabled */
	priv->enabled = true;
	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)
{
	int ret;

	/* allow multiple disable */
	if (!priv->enabled)
		return 0;

	/* switch to the internal GPIO IRQ line */
	data_disable_interrupts(priv);

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

	/*
	 * wait for all outstanding DMA to complete
	 *
	 * Device interrupts are disabled, therefore another buffer cannot
	 * be marked inflight.
	 */
	ret = wait_event_interruptible(priv->wait, priv->inflight == NULL);
	if (ret)
		return ret;

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

	/*
	 * We are taking the spinlock not to protect priv->enabled, but instead
	 * to make sure that there are no readers in the process of altering
	 * the free or used lists while we are setting this flag.
	 */
	spin_lock_irq(&priv->lock);
	priv->enabled = false;
	spin_unlock_irq(&priv->lock);

	/* 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;
	int ret;

	/*
	 * Lock the mutex first, so that we get an accurate value for enable
	 * Lock the spinlock next, to get accurate list counts
	 */
	ret = mutex_lock_interruptible(&priv->mutex);
	if (ret)
		return ret;

	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);
	mutex_unlock(&priv->mutex);
	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);
	return snprintf(buf, PAGE_SIZE, "%u\n", priv->enabled);
}

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

	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;
	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.
	 */
	if (!priv->enabled || dbuf->size != priv->bufsize) {
		videobuf_dma_unmap(priv->dev, &dbuf->vb);
		data_free_buffer(dbuf);
		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);
	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;
	}

	/* IO memory (stop cacheing) */
	vma->vm_flags |= VM_IO | VM_RESERVED;
	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;
	}

	dev_set_drvdata(&op->dev, 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 = dev_get_drvdata(&op->dev);
	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 Init / Exit
 */

static int __init data_init(void)
{
	return platform_driver_register(&data_of_driver);
}

static void __exit data_exit(void)
{
	platform_driver_unregister(&data_of_driver);
}

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

module_init(data_init);
module_exit(data_exit);