drivers/char/ipmi/bt-bmc.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (c) 2015-2016, IBM Corporation.
  */

 #include <linux/atomic.h>
 #include <linux/bt-bmc.h>
 #include <linux/errno.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/miscdevice.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/poll.h>
 #include <linux/sched.h>
 #include <linux/timer.h>

 /*
  * This is a BMC device used to communicate to the host
  */
 #define DEVICE_NAME	"ipmi-bt-host"

 #define BT_IO_BASE	0xe4
 #define BT_IRQ		10

 #define BT_CR0		0x0
 #define   BT_CR0_IO_BASE		16
 #define   BT_CR0_IRQ			12
 #define   BT_CR0_EN_CLR_SLV_RDP		0x8
 #define   BT_CR0_EN_CLR_SLV_WRP		0x4
 #define   BT_CR0_ENABLE_IBT		0x1
 #define BT_CR1		0x4
 #define   BT_CR1_IRQ_H2B	0x01
 #define   BT_CR1_IRQ_HBUSY	0x40
 #define BT_CR2		0x8
 #define   BT_CR2_IRQ_H2B	0x01
 #define   BT_CR2_IRQ_HBUSY	0x40
 #define BT_CR3		0xc
 #define BT_CTRL		0x10
 #define   BT_CTRL_B_BUSY		0x80
 #define   BT_CTRL_H_BUSY		0x40
 #define   BT_CTRL_OEM0			0x20
 #define   BT_CTRL_SMS_ATN		0x10
 #define   BT_CTRL_B2H_ATN		0x08
 #define   BT_CTRL_H2B_ATN		0x04
 #define   BT_CTRL_CLR_RD_PTR		0x02
 #define   BT_CTRL_CLR_WR_PTR		0x01
 #define BT_BMC2HOST	0x14
 #define BT_INTMASK	0x18
 #define   BT_INTMASK_B2H_IRQEN		0x01
 #define   BT_INTMASK_B2H_IRQ		0x02
 #define   BT_INTMASK_BMC_HWRST		0x80

 #define BT_BMC_BUFFER_SIZE 256

 struct bt_bmc {
 	struct device		dev;
 	struct miscdevice	miscdev;
 	void __iomem		*base;
 	int			irq;
 	wait_queue_head_t	queue;
 	struct timer_list	poll_timer;
 	struct mutex		mutex;
 };

 static atomic_t open_count = ATOMIC_INIT(0);

 static u8 bt_inb(struct bt_bmc *bt_bmc, int reg)
 {
 	return readb(bt_bmc->base + reg);
 }

 static void bt_outb(struct bt_bmc *bt_bmc, u8 data, int reg)
 {
 	writeb(data, bt_bmc->base + reg);
 }

 static void clr_rd_ptr(struct bt_bmc *bt_bmc)
 {
 	bt_outb(bt_bmc, BT_CTRL_CLR_RD_PTR, BT_CTRL);
 }

 static void clr_wr_ptr(struct bt_bmc *bt_bmc)
 {
 	bt_outb(bt_bmc, BT_CTRL_CLR_WR_PTR, BT_CTRL);
 }

 static void clr_h2b_atn(struct bt_bmc *bt_bmc)
 {
 	bt_outb(bt_bmc, BT_CTRL_H2B_ATN, BT_CTRL);
 }

 static void set_b_busy(struct bt_bmc *bt_bmc)
 {
 	if (!(bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_B_BUSY))
 		bt_outb(bt_bmc, BT_CTRL_B_BUSY, BT_CTRL);
 }

 static void clr_b_busy(struct bt_bmc *bt_bmc)
 {
 	if (bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_B_BUSY)
 		bt_outb(bt_bmc, BT_CTRL_B_BUSY, BT_CTRL);
 }

 static void set_b2h_atn(struct bt_bmc *bt_bmc)
 {
 	bt_outb(bt_bmc, BT_CTRL_B2H_ATN, BT_CTRL);
 }

 static u8 bt_read(struct bt_bmc *bt_bmc)
 {
 	return bt_inb(bt_bmc, BT_BMC2HOST);
 }

 static ssize_t bt_readn(struct bt_bmc *bt_bmc, u8 *buf, size_t n)
 {
 	int i;

 	for (i = 0; i < n; i++)
 		buf[i] = bt_read(bt_bmc);
 	return n;
 }

 static void bt_write(struct bt_bmc *bt_bmc, u8 c)
 {
 	bt_outb(bt_bmc, c, BT_BMC2HOST);
 }

 static ssize_t bt_writen(struct bt_bmc *bt_bmc, u8 *buf, size_t n)
 {
 	int i;

 	for (i = 0; i < n; i++)
 		bt_write(bt_bmc, buf[i]);
 	return n;
 }

 static void set_sms_atn(struct bt_bmc *bt_bmc)
 {
 	bt_outb(bt_bmc, BT_CTRL_SMS_ATN, BT_CTRL);
 }

 static struct bt_bmc *file_bt_bmc(struct file *file)
 {
 	return container_of(file->private_data, struct bt_bmc, miscdev);
 }

 static int bt_bmc_open(struct inode *inode, struct file *file)
 {
 	struct bt_bmc *bt_bmc = file_bt_bmc(file);

 	if (atomic_inc_return(&open_count) == 1) {
 		clr_b_busy(bt_bmc);
 		return 0;
 	}

 	atomic_dec(&open_count);
 	return -EBUSY;
 }

 /*
  * The BT (Block Transfer) interface means that entire messages are
  * buffered by the host before a notification is sent to the BMC that
  * there is data to be read. The first byte is the length and the
  * message data follows. The read operation just tries to capture the
  * whole before returning it to userspace.
  *
  * BT Message format :
  *
  *    Byte 1  Byte 2     Byte 3  Byte 4  Byte 5:N
  *    Length  NetFn/LUN  Seq     Cmd     Data
  *
  */
 static ssize_t bt_bmc_read(struct file *file, char __user *buf,
 			   size_t count, loff_t *ppos)
 {
 	struct bt_bmc *bt_bmc = file_bt_bmc(file);
 	u8 len;
 	int len_byte = 1;
 	u8 kbuffer[BT_BMC_BUFFER_SIZE];
 	ssize_t ret = 0;
 	ssize_t nread;

 	WARN_ON(*ppos);

 	if (wait_event_interruptible(bt_bmc->queue,
 				     bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_H2B_ATN))
 		return -ERESTARTSYS;

 	mutex_lock(&bt_bmc->mutex);

 	if (unlikely(!(bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_H2B_ATN))) {
 		ret = -EIO;
 		goto out_unlock;
 	}

 	set_b_busy(bt_bmc);
 	clr_h2b_atn(bt_bmc);
 	clr_rd_ptr(bt_bmc);

 	/*
 	 * The BT frames start with the message length, which does not
 	 * include the length byte.
 	 */
 	kbuffer[0] = bt_read(bt_bmc);
 	len = kbuffer[0];

 	/* We pass the length back to userspace as well */
 	if (len + 1 > count)
 		len = count - 1;

 	while (len) {
 		nread = min_t(ssize_t, len, sizeof(kbuffer) - len_byte);

 		bt_readn(bt_bmc, kbuffer + len_byte, nread);

 		if (copy_to_user(buf, kbuffer, nread + len_byte)) {
 			ret = -EFAULT;
 			break;
 		}
 		len -= nread;
 		buf += nread + len_byte;
 		ret += nread + len_byte;
 		len_byte = 0;
 	}

 	clr_b_busy(bt_bmc);

 out_unlock:
 	mutex_unlock(&bt_bmc->mutex);
 	return ret;
 }

 /*
  * BT Message response format :
  *
  *    Byte 1  Byte 2     Byte 3  Byte 4  Byte 5  Byte 6:N
  *    Length  NetFn/LUN  Seq     Cmd     Code    Data
  */
 static ssize_t bt_bmc_write(struct file *file, const char __user *buf,
 			    size_t count, loff_t *ppos)
 {
 	struct bt_bmc *bt_bmc = file_bt_bmc(file);
 	u8 kbuffer[BT_BMC_BUFFER_SIZE];
 	ssize_t ret = 0;
 	ssize_t nwritten;

 	/*
 	 * send a minimum response size
 	 */
 	if (count < 5)
 		return -EINVAL;

 	WARN_ON(*ppos);

 	/*
 	 * There's no interrupt for clearing bmc busy so we have to
 	 * poll
 	 */
 	if (wait_event_interruptible(bt_bmc->queue,
 				     !(bt_inb(bt_bmc, BT_CTRL) &
 				       (BT_CTRL_H_BUSY | BT_CTRL_B2H_ATN))))
 		return -ERESTARTSYS;

 	mutex_lock(&bt_bmc->mutex);

 	if (unlikely(bt_inb(bt_bmc, BT_CTRL) &
 		     (BT_CTRL_H_BUSY | BT_CTRL_B2H_ATN))) {
 		ret = -EIO;
 		goto out_unlock;
 	}

 	clr_wr_ptr(bt_bmc);

 	while (count) {
 		nwritten = min_t(ssize_t, count, sizeof(kbuffer));
 		if (copy_from_user(&kbuffer, buf, nwritten)) {
 			ret = -EFAULT;
 			break;
 		}

 		bt_writen(bt_bmc, kbuffer, nwritten);

 		count -= nwritten;
 		buf += nwritten;
 		ret += nwritten;
 	}

 	set_b2h_atn(bt_bmc);

 out_unlock:
 	mutex_unlock(&bt_bmc->mutex);
 	return ret;
 }

 static long bt_bmc_ioctl(struct file *file, unsigned int cmd,
 			 unsigned long param)
 {
 	struct bt_bmc *bt_bmc = file_bt_bmc(file);

 	switch (cmd) {
 	case BT_BMC_IOCTL_SMS_ATN:
 		set_sms_atn(bt_bmc);
 		return 0;
 	}
 	return -EINVAL;
 }

 static int bt_bmc_release(struct inode *inode, struct file *file)
 {
 	struct bt_bmc *bt_bmc = file_bt_bmc(file);

 	atomic_dec(&open_count);
 	set_b_busy(bt_bmc);
 	return 0;
 }

 static __poll_t bt_bmc_poll(struct file *file, poll_table *wait)
 {
 	struct bt_bmc *bt_bmc = file_bt_bmc(file);
 	__poll_t mask = 0;
 	u8 ctrl;

 	poll_wait(file, &bt_bmc->queue, wait);

 	ctrl = bt_inb(bt_bmc, BT_CTRL);

 	if (ctrl & BT_CTRL_H2B_ATN)
 		mask |= EPOLLIN;

 	if (!(ctrl & (BT_CTRL_H_BUSY | BT_CTRL_B2H_ATN)))
 		mask |= EPOLLOUT;

 	return mask;
 }

 static const struct file_operations bt_bmc_fops = {
 	.owner		= THIS_MODULE,
 	.open		= bt_bmc_open,
 	.read		= bt_bmc_read,
 	.write		= bt_bmc_write,
 	.release	= bt_bmc_release,
 	.poll		= bt_bmc_poll,
 	.unlocked_ioctl	= bt_bmc_ioctl,
 };

 static void poll_timer(struct timer_list *t)
 {
 	struct bt_bmc *bt_bmc = from_timer(bt_bmc, t, poll_timer);

 	bt_bmc->poll_timer.expires += msecs_to_jiffies(500);
 	wake_up(&bt_bmc->queue);
 	add_timer(&bt_bmc->poll_timer);
 }

 static irqreturn_t bt_bmc_irq(int irq, void *arg)
 {
 	struct bt_bmc *bt_bmc = arg;
 	u32 reg;

 	reg = readl(bt_bmc->base + BT_CR2);

 	reg &= BT_CR2_IRQ_H2B | BT_CR2_IRQ_HBUSY;
 	if (!reg)
 		return IRQ_NONE;

 	/* ack pending IRQs */
 	writel(reg, bt_bmc->base + BT_CR2);

 	wake_up(&bt_bmc->queue);
 	return IRQ_HANDLED;
 }

 static int bt_bmc_config_irq(struct bt_bmc *bt_bmc,
 			     struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	int rc;
 	u32 reg;

 	bt_bmc->irq = platform_get_irq_optional(pdev, 0);
 	if (bt_bmc->irq < 0)
 		return bt_bmc->irq;

 	rc = devm_request_irq(dev, bt_bmc->irq, bt_bmc_irq, IRQF_SHARED,
 			      DEVICE_NAME, bt_bmc);
 	if (rc < 0) {
 		dev_warn(dev, "Unable to request IRQ %d\n", bt_bmc->irq);
 		bt_bmc->irq = rc;
 		return rc;
 	}

 	/*
 	 * Configure IRQs on the bmc clearing the H2B and HBUSY bits;
 	 * H2B will be asserted when the bmc has data for us; HBUSY
 	 * will be cleared (along with B2H) when we can write the next
 	 * message to the BT buffer
 	 */
 	reg = readl(bt_bmc->base + BT_CR1);
 	reg |= BT_CR1_IRQ_H2B | BT_CR1_IRQ_HBUSY;
 	writel(reg, bt_bmc->base + BT_CR1);

 	return 0;
 }

 static int bt_bmc_probe(struct platform_device *pdev)
 {
 	struct bt_bmc *bt_bmc;
 	struct device *dev;
 	int rc;

 	dev = &pdev->dev;
 	dev_info(dev, "Found bt bmc device\n");

 	bt_bmc = devm_kzalloc(dev, sizeof(*bt_bmc), GFP_KERNEL);
 	if (!bt_bmc)
 		return -ENOMEM;

 	dev_set_drvdata(&pdev->dev, bt_bmc);

 	bt_bmc->base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(bt_bmc->base))
 		return PTR_ERR(bt_bmc->base);

 	mutex_init(&bt_bmc->mutex);
 	init_waitqueue_head(&bt_bmc->queue);

 	bt_bmc->miscdev.minor	= MISC_DYNAMIC_MINOR;
 	bt_bmc->miscdev.name	= DEVICE_NAME;
 	bt_bmc->miscdev.fops	= &bt_bmc_fops;
 	bt_bmc->miscdev.parent = dev;
 	rc = misc_register(&bt_bmc->miscdev);
 	if (rc) {
 		dev_err(dev, "Unable to register misc device\n");
 		return rc;
 	}

 	bt_bmc_config_irq(bt_bmc, pdev);

 	if (bt_bmc->irq >= 0) {
 		dev_info(dev, "Using IRQ %d\n", bt_bmc->irq);
 	} else {
 		dev_info(dev, "No IRQ; using timer\n");
 		timer_setup(&bt_bmc->poll_timer, poll_timer, 0);
 		bt_bmc->poll_timer.expires = jiffies + msecs_to_jiffies(10);
 		add_timer(&bt_bmc->poll_timer);
 	}

 	writel((BT_IO_BASE << BT_CR0_IO_BASE) |
 		     (BT_IRQ << BT_CR0_IRQ) |
 		     BT_CR0_EN_CLR_SLV_RDP |
 		     BT_CR0_EN_CLR_SLV_WRP |
 		     BT_CR0_ENABLE_IBT,
 		bt_bmc->base + BT_CR0);

 	clr_b_busy(bt_bmc);

 	return 0;
 }

 static int bt_bmc_remove(struct platform_device *pdev)
 {
 	struct bt_bmc *bt_bmc = dev_get_drvdata(&pdev->dev);

 	misc_deregister(&bt_bmc->miscdev);
 	if (bt_bmc->irq < 0)
 		del_timer_sync(&bt_bmc->poll_timer);
 	return 0;
 }

 static const struct of_device_id bt_bmc_match[] = {
 	{ .compatible = "aspeed,ast2400-ibt-bmc" },
 	{ .compatible = "aspeed,ast2500-ibt-bmc" },
 	{ .compatible = "aspeed,ast2600-ibt-bmc" },
 	{ },
 };

 static struct platform_driver bt_bmc_driver = {
 	.driver = {
 		.name		= DEVICE_NAME,
 		.of_match_table = bt_bmc_match,
 	},
 	.probe = bt_bmc_probe,
 	.remove = bt_bmc_remove,
 };

 module_platform_driver(bt_bmc_driver);

 MODULE_DEVICE_TABLE(of, bt_bmc_match);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Alistair Popple <alistair@popple.id.au>");
 MODULE_DESCRIPTION("Linux device interface to the IPMI BT interface");
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* Copyright (c) 2015-2016, IBM Corporation.
	*/

	#include <linux/atomic.h>
	#include <linux/bt-bmc.h>
	#include <linux/errno.h>
	#include <linux/interrupt.h>
	#include <linux/io.h>
	#include <linux/miscdevice.h>
	#include <linux/module.h>
	#include <linux/of.h>
	#include <linux/platform_device.h>
	#include <linux/poll.h>
	#include <linux/sched.h>
	#include <linux/timer.h>

	/*
	* This is a BMC device used to communicate to the host
	*/
	#define DEVICE_NAME "ipmi-bt-host"

	#define BT_IO_BASE 0xe4
	#define BT_IRQ 10

	#define BT_CR0 0x0
	#define BT_CR0_IO_BASE 16
	#define BT_CR0_IRQ 12
	#define BT_CR0_EN_CLR_SLV_RDP 0x8
	#define BT_CR0_EN_CLR_SLV_WRP 0x4
	#define BT_CR0_ENABLE_IBT 0x1
	#define BT_CR1 0x4
	#define BT_CR1_IRQ_H2B 0x01
	#define BT_CR1_IRQ_HBUSY 0x40
	#define BT_CR2 0x8
	#define BT_CR2_IRQ_H2B 0x01
	#define BT_CR2_IRQ_HBUSY 0x40
	#define BT_CR3 0xc
	#define BT_CTRL 0x10
	#define BT_CTRL_B_BUSY 0x80
	#define BT_CTRL_H_BUSY 0x40
	#define BT_CTRL_OEM0 0x20
	#define BT_CTRL_SMS_ATN 0x10
	#define BT_CTRL_B2H_ATN 0x08
	#define BT_CTRL_H2B_ATN 0x04
	#define BT_CTRL_CLR_RD_PTR 0x02
	#define BT_CTRL_CLR_WR_PTR 0x01
	#define BT_BMC2HOST 0x14
	#define BT_INTMASK 0x18
	#define BT_INTMASK_B2H_IRQEN 0x01
	#define BT_INTMASK_B2H_IRQ 0x02
	#define BT_INTMASK_BMC_HWRST 0x80

	#define BT_BMC_BUFFER_SIZE 256

	struct bt_bmc {
	struct device dev;
	struct miscdevice miscdev;
	void __iomem *base;
	int irq;
	wait_queue_head_t queue;
	struct timer_list poll_timer;
	struct mutex mutex;
	};

	static atomic_t open_count = ATOMIC_INIT(0);

	static u8 bt_inb(struct bt_bmc *bt_bmc, int reg)
	{
	return readb(bt_bmc->base + reg);
	}

	static void bt_outb(struct bt_bmc *bt_bmc, u8 data, int reg)
	{
	writeb(data, bt_bmc->base + reg);
	}

	static void clr_rd_ptr(struct bt_bmc *bt_bmc)
	{
	bt_outb(bt_bmc, BT_CTRL_CLR_RD_PTR, BT_CTRL);
	}

	static void clr_wr_ptr(struct bt_bmc *bt_bmc)
	{
	bt_outb(bt_bmc, BT_CTRL_CLR_WR_PTR, BT_CTRL);
	}

	static void clr_h2b_atn(struct bt_bmc *bt_bmc)
	{
	bt_outb(bt_bmc, BT_CTRL_H2B_ATN, BT_CTRL);
	}

	static void set_b_busy(struct bt_bmc *bt_bmc)
	{
	if (!(bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_B_BUSY))
	bt_outb(bt_bmc, BT_CTRL_B_BUSY, BT_CTRL);
	}

	static void clr_b_busy(struct bt_bmc *bt_bmc)
	{
	if (bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_B_BUSY)
	bt_outb(bt_bmc, BT_CTRL_B_BUSY, BT_CTRL);
	}

	static void set_b2h_atn(struct bt_bmc *bt_bmc)
	{
	bt_outb(bt_bmc, BT_CTRL_B2H_ATN, BT_CTRL);
	}

	static u8 bt_read(struct bt_bmc *bt_bmc)
	{
	return bt_inb(bt_bmc, BT_BMC2HOST);
	}

	static ssize_t bt_readn(struct bt_bmc bt_bmc, u8 buf, size_t n)
	{
	int i;

	for (i = 0; i < n; i++)
	buf[i] = bt_read(bt_bmc);
	return n;
	}

	static void bt_write(struct bt_bmc *bt_bmc, u8 c)
	{
	bt_outb(bt_bmc, c, BT_BMC2HOST);
	}

	static ssize_t bt_writen(struct bt_bmc bt_bmc, u8 buf, size_t n)
	{
	int i;

	for (i = 0; i < n; i++)
	bt_write(bt_bmc, buf[i]);
	return n;
	}

	static void set_sms_atn(struct bt_bmc *bt_bmc)
	{
	bt_outb(bt_bmc, BT_CTRL_SMS_ATN, BT_CTRL);
	}

	static struct bt_bmc file_bt_bmc(struct file file)
	{
	return container_of(file->private_data, struct bt_bmc, miscdev);
	}

	static int bt_bmc_open(struct inode inode, struct file file)
	{
	struct bt_bmc *bt_bmc = file_bt_bmc(file);

	if (atomic_inc_return(&open_count) == 1) {
	clr_b_busy(bt_bmc);
	return 0;
	}

	atomic_dec(&open_count);
	return -EBUSY;
	}

	/*
	* The BT (Block Transfer) interface means that entire messages are
	* buffered by the host before a notification is sent to the BMC that
	* there is data to be read. The first byte is the length and the
	* message data follows. The read operation just tries to capture the
	* whole before returning it to userspace.
	*
	* BT Message format :
	*
	* Byte 1 Byte 2 Byte 3 Byte 4 Byte 5:N
	* Length NetFn/LUN Seq Cmd Data
	*
	*/
	static ssize_t bt_bmc_read(struct file file, char __user buf,
	size_t count, loff_t *ppos)
	{
	struct bt_bmc *bt_bmc = file_bt_bmc(file);
	u8 len;
	int len_byte = 1;
	u8 kbuffer[BT_BMC_BUFFER_SIZE];
	ssize_t ret = 0;
	ssize_t nread;

	WARN_ON(*ppos);

	if (wait_event_interruptible(bt_bmc->queue,
	bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_H2B_ATN))
	return -ERESTARTSYS;

	mutex_lock(&bt_bmc->mutex);

	if (unlikely(!(bt_inb(bt_bmc, BT_CTRL) & BT_CTRL_H2B_ATN))) {
	ret = -EIO;
	goto out_unlock;
	}

	set_b_busy(bt_bmc);
	clr_h2b_atn(bt_bmc);
	clr_rd_ptr(bt_bmc);

	/*
	* The BT frames start with the message length, which does not
	* include the length byte.
	*/
	kbuffer[0] = bt_read(bt_bmc);
	len = kbuffer[0];

	/* We pass the length back to userspace as well */
	if (len + 1 > count)
	len = count - 1;

	while (len) {
	nread = min_t(ssize_t, len, sizeof(kbuffer) - len_byte);

	bt_readn(bt_bmc, kbuffer + len_byte, nread);

	if (copy_to_user(buf, kbuffer, nread + len_byte)) {
	ret = -EFAULT;
	break;
	}
	len -= nread;
	buf += nread + len_byte;
	ret += nread + len_byte;
	len_byte = 0;
	}

	clr_b_busy(bt_bmc);

	out_unlock:
	mutex_unlock(&bt_bmc->mutex);
	return ret;
	}

	/*
	* BT Message response format :
	*
	* Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6:N
	* Length NetFn/LUN Seq Cmd Code Data
	*/
	static ssize_t bt_bmc_write(struct file file, const char __user buf,
	size_t count, loff_t *ppos)
	{
	struct bt_bmc *bt_bmc = file_bt_bmc(file);
	u8 kbuffer[BT_BMC_BUFFER_SIZE];
	ssize_t ret = 0;
	ssize_t nwritten;

	/*
	* send a minimum response size
	*/
	if (count < 5)
	return -EINVAL;

	WARN_ON(*ppos);

	/*
	* There's no interrupt for clearing bmc busy so we have to
	* poll
	*/
	if (wait_event_interruptible(bt_bmc->queue,
	!(bt_inb(bt_bmc, BT_CTRL) &
	(BT_CTRL_H_BUSY \| BT_CTRL_B2H_ATN))))
	return -ERESTARTSYS;

	mutex_lock(&bt_bmc->mutex);

	if (unlikely(bt_inb(bt_bmc, BT_CTRL) &
	(BT_CTRL_H_BUSY \| BT_CTRL_B2H_ATN))) {
	ret = -EIO;
	goto out_unlock;
	}

	clr_wr_ptr(bt_bmc);

	while (count) {
	nwritten = min_t(ssize_t, count, sizeof(kbuffer));
	if (copy_from_user(&kbuffer, buf, nwritten)) {
	ret = -EFAULT;
	break;
	}

	bt_writen(bt_bmc, kbuffer, nwritten);

	count -= nwritten;
	buf += nwritten;
	ret += nwritten;
	}

	set_b2h_atn(bt_bmc);

	out_unlock:
	mutex_unlock(&bt_bmc->mutex);
	return ret;
	}

	static long bt_bmc_ioctl(struct file *file, unsigned int cmd,
	unsigned long param)
	{
	struct bt_bmc *bt_bmc = file_bt_bmc(file);

	switch (cmd) {
	case BT_BMC_IOCTL_SMS_ATN:
	set_sms_atn(bt_bmc);
	return 0;
	}
	return -EINVAL;
	}

	static int bt_bmc_release(struct inode inode, struct file file)
	{
	struct bt_bmc *bt_bmc = file_bt_bmc(file);

	atomic_dec(&open_count);
	set_b_busy(bt_bmc);
	return 0;
	}

	static __poll_t bt_bmc_poll(struct file file, poll_table wait)
	{
	struct bt_bmc *bt_bmc = file_bt_bmc(file);
	__poll_t mask = 0;
	u8 ctrl;

	poll_wait(file, &bt_bmc->queue, wait);

	ctrl = bt_inb(bt_bmc, BT_CTRL);

	if (ctrl & BT_CTRL_H2B_ATN)
	mask \|= EPOLLIN;

	if (!(ctrl & (BT_CTRL_H_BUSY \| BT_CTRL_B2H_ATN)))
	mask \|= EPOLLOUT;

	return mask;
	}

	static const struct file_operations bt_bmc_fops = {
	.owner = THIS_MODULE,
	.open = bt_bmc_open,
	.read = bt_bmc_read,
	.write = bt_bmc_write,
	.release = bt_bmc_release,
	.poll = bt_bmc_poll,
	.unlocked_ioctl = bt_bmc_ioctl,
	};

	static void poll_timer(struct timer_list *t)
	{
	struct bt_bmc *bt_bmc = from_timer(bt_bmc, t, poll_timer);

	bt_bmc->poll_timer.expires += msecs_to_jiffies(500);
	wake_up(&bt_bmc->queue);
	add_timer(&bt_bmc->poll_timer);
	}

	static irqreturn_t bt_bmc_irq(int irq, void *arg)
	{
	struct bt_bmc *bt_bmc = arg;
	u32 reg;

	reg = readl(bt_bmc->base + BT_CR2);

	reg &= BT_CR2_IRQ_H2B \| BT_CR2_IRQ_HBUSY;
	if (!reg)
	return IRQ_NONE;

	/* ack pending IRQs */
	writel(reg, bt_bmc->base + BT_CR2);

	wake_up(&bt_bmc->queue);
	return IRQ_HANDLED;
	}

	static int bt_bmc_config_irq(struct bt_bmc *bt_bmc,
	struct platform_device *pdev)
	{
	struct device *dev = &pdev->dev;
	int rc;
	u32 reg;

	bt_bmc->irq = platform_get_irq_optional(pdev, 0);
	if (bt_bmc->irq < 0)
	return bt_bmc->irq;

	rc = devm_request_irq(dev, bt_bmc->irq, bt_bmc_irq, IRQF_SHARED,
	DEVICE_NAME, bt_bmc);
	if (rc < 0) {
	dev_warn(dev, "Unable to request IRQ %d\n", bt_bmc->irq);
	bt_bmc->irq = rc;
	return rc;
	}

	/*
	* Configure IRQs on the bmc clearing the H2B and HBUSY bits;
	* H2B will be asserted when the bmc has data for us; HBUSY
	* will be cleared (along with B2H) when we can write the next
	* message to the BT buffer
	*/
	reg = readl(bt_bmc->base + BT_CR1);
	reg \|= BT_CR1_IRQ_H2B \| BT_CR1_IRQ_HBUSY;
	writel(reg, bt_bmc->base + BT_CR1);

	return 0;
	}

	static int bt_bmc_probe(struct platform_device *pdev)
	{
	struct bt_bmc *bt_bmc;
	struct device *dev;
	int rc;

	dev = &pdev->dev;
	dev_info(dev, "Found bt bmc device\n");

	bt_bmc = devm_kzalloc(dev, sizeof(*bt_bmc), GFP_KERNEL);
	if (!bt_bmc)
	return -ENOMEM;

	dev_set_drvdata(&pdev->dev, bt_bmc);

	bt_bmc->base = devm_platform_ioremap_resource(pdev, 0);
	if (IS_ERR(bt_bmc->base))
	return PTR_ERR(bt_bmc->base);

	mutex_init(&bt_bmc->mutex);
	init_waitqueue_head(&bt_bmc->queue);

	bt_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
	bt_bmc->miscdev.name = DEVICE_NAME;
	bt_bmc->miscdev.fops = &bt_bmc_fops;
	bt_bmc->miscdev.parent = dev;
	rc = misc_register(&bt_bmc->miscdev);
	if (rc) {
	dev_err(dev, "Unable to register misc device\n");
	return rc;
	}

	bt_bmc_config_irq(bt_bmc, pdev);

	if (bt_bmc->irq >= 0) {
	dev_info(dev, "Using IRQ %d\n", bt_bmc->irq);
	} else {
	dev_info(dev, "No IRQ; using timer\n");
	timer_setup(&bt_bmc->poll_timer, poll_timer, 0);
	bt_bmc->poll_timer.expires = jiffies + msecs_to_jiffies(10);
	add_timer(&bt_bmc->poll_timer);
	}

	writel((BT_IO_BASE << BT_CR0_IO_BASE) \|
	(BT_IRQ << BT_CR0_IRQ) \|
	BT_CR0_EN_CLR_SLV_RDP \|
	BT_CR0_EN_CLR_SLV_WRP \|
	BT_CR0_ENABLE_IBT,
	bt_bmc->base + BT_CR0);

	clr_b_busy(bt_bmc);

	return 0;
	}

	static int bt_bmc_remove(struct platform_device *pdev)
	{
	struct bt_bmc *bt_bmc = dev_get_drvdata(&pdev->dev);

	misc_deregister(&bt_bmc->miscdev);
	if (bt_bmc->irq < 0)
	del_timer_sync(&bt_bmc->poll_timer);
	return 0;
	}

	static const struct of_device_id bt_bmc_match[] = {
	{ .compatible = "aspeed,ast2400-ibt-bmc" },
	{ .compatible = "aspeed,ast2500-ibt-bmc" },
	{ .compatible = "aspeed,ast2600-ibt-bmc" },
	{ },
	};

	static struct platform_driver bt_bmc_driver = {
	.driver = {
	.name = DEVICE_NAME,
	.of_match_table = bt_bmc_match,
	},
	.probe = bt_bmc_probe,
	.remove = bt_bmc_remove,
	};

	module_platform_driver(bt_bmc_driver);

	MODULE_DEVICE_TABLE(of, bt_bmc_match);
	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("Alistair Popple <alistair@popple.id.au>");
	MODULE_DESCRIPTION("Linux device interface to the IPMI BT interface");