// SPDX-License-Identifier: GPL-2.0

  /* ePAPR hypervisor byte channel device driver
   *
   * Copyright 2009-2011 Freescale Semiconductor, Inc.
   *
   * Author: Timur Tabi <timur@freescale.com>
   *

   * This driver support three distinct interfaces, all of which are related to
   * ePAPR hypervisor byte channels.
   *
   * 1) An early-console (udbg) driver.  This provides early console output
   * through a byte channel.  The byte channel handle must be specified in a
   * Kconfig option.
   *
   * 2) A normal console driver.  Output is sent to the byte channel designated
   * for stdout in the device tree.  The console driver is for handling kernel
   * printk calls.
   *
   * 3) A tty driver, which is used to handle user-space input and output.  The
   * byte channel used for the console is designated as the default tty.
   */

  #include <linux/init.h>
  #include <linux/slab.h>
  #include <linux/err.h>
  #include <linux/interrupt.h>
  #include <linux/fs.h>
  #include <linux/poll.h>
  #include <asm/epapr_hcalls.h>
  #include <linux/of.h>

  #include <linux/of_irq.h>

  #include <linux/platform_device.h>
  #include <linux/cdev.h>
  #include <linux/console.h>
  #include <linux/tty.h>
  #include <linux/tty_flip.h>
  #include <linux/circ_buf.h>
  #include <asm/udbg.h>
  
  /* The size of the transmit circular buffer.  This must be a power of two. */
  #define BUF_SIZE	2048
  
  /* Per-byte channel private data */
  struct ehv_bc_data {
  	struct device *dev;
  	struct tty_port port;
  	uint32_t handle;
  	unsigned int rx_irq;
  	unsigned int tx_irq;
  
  	spinlock_t lock;	/* lock for transmit buffer */
  	unsigned char buf[BUF_SIZE];	/* transmit circular buffer */
  	unsigned int head;	/* circular buffer head */
  	unsigned int tail;	/* circular buffer tail */
  
  	int tx_irq_enabled;	/* true == TX interrupt is enabled */
  };
  
  /* Array of byte channel objects */
  static struct ehv_bc_data *bcs;
  
  /* Byte channel handle for stdout (and stdin), taken from device tree */
  static unsigned int stdout_bc;
  
  /* Virtual IRQ for the byte channel handle for stdin, taken from device tree */
  static unsigned int stdout_irq;
  
  /**************************** SUPPORT FUNCTIONS ****************************/
  
  /*
   * Enable the transmit interrupt
   *
   * Unlike a serial device, byte channels have no mechanism for disabling their
   * own receive or transmit interrupts.  To emulate that feature, we toggle
   * the IRQ in the kernel.
   *
   * We cannot just blindly call enable_irq() or disable_irq(), because these
   * calls are reference counted.  This means that we cannot call enable_irq()
   * if interrupts are already enabled.  This can happen in two situations:
   *
   * 1. The tty layer makes two back-to-back calls to ehv_bc_tty_write()
   * 2. A transmit interrupt occurs while executing ehv_bc_tx_dequeue()
   *
   * To work around this, we keep a flag to tell us if the IRQ is enabled or not.
   */
  static void enable_tx_interrupt(struct ehv_bc_data *bc)
  {
  	if (!bc->tx_irq_enabled) {
  		enable_irq(bc->tx_irq);
  		bc->tx_irq_enabled = 1;
  	}
  }
  
  static void disable_tx_interrupt(struct ehv_bc_data *bc)
  {
  	if (bc->tx_irq_enabled) {
  		disable_irq_nosync(bc->tx_irq);
  		bc->tx_irq_enabled = 0;
  	}
  }
  
  /*
   * find the byte channel handle to use for the console
   *
   * The byte channel to be used for the console is specified via a "stdout"
   * property in the /chosen node.

   */
  static int find_console_handle(void)
  {

  	struct device_node *np = of_stdout;

  	const uint32_t *iprop;

  	/* We don't care what the aliased node is actually called.  We only
  	 * care if it's compatible with "epapr,hv-byte-channel", because that

  	 * indicates that it's a byte channel node.

  	 */

  	if (!np || !of_device_is_compatible(np, "epapr,hv-byte-channel"))

  		return 0;

  
  	stdout_irq = irq_of_parse_and_map(np, 0);
  	if (stdout_irq == NO_IRQ) {

  		pr_err("ehv-bc: no 'interrupts' property in %pOF node
  ", np);

  		return 0;
  	}
  
  	/*
  	 * The 'hv-handle' property contains the handle for this byte channel.
  	 */
  	iprop = of_get_property(np, "hv-handle", NULL);
  	if (!iprop) {

  		pr_err("ehv-bc: no 'hv-handle' property in %pOFn node
  ",
  		       np);

  		return 0;
  	}
  	stdout_bc = be32_to_cpu(*iprop);

  	return 1;
  }

  static unsigned int local_ev_byte_channel_send(unsigned int handle,
  					       unsigned int *count,
  					       const char *p)
  {
  	char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
  	unsigned int c = *count;
  
  	if (c < sizeof(buffer)) {
  		memcpy(buffer, p, c);
  		memset(&buffer[c], 0, sizeof(buffer) - c);
  		p = buffer;
  	}
  	return ev_byte_channel_send(handle, count, p);
  }

  /*************************** EARLY CONSOLE DRIVER ***************************/
  
  #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
  
  /*
   * send a byte to a byte channel, wait if necessary
   *
   * This function sends a byte to a byte channel, and it waits and
   * retries if the byte channel is full.  It returns if the character
   * has been sent, or if some error has occurred.
   *
   */
  static void byte_channel_spin_send(const char data)
  {
  	int ret, count;
  
  	do {
  		count = 1;

  		ret = local_ev_byte_channel_send(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,

  					   &count, &data);
  	} while (ret == EV_EAGAIN);
  }
  
  /*
   * The udbg subsystem calls this function to display a single character.
   * We convert CR to a CR/LF.
   */
  static void ehv_bc_udbg_putc(char c)
  {
  	if (c == '
  ')
  		byte_channel_spin_send('\r');
  
  	byte_channel_spin_send(c);
  }
  
  /*
   * early console initialization
   *
   * PowerPC kernels support an early printk console, also known as udbg.
   * This function must be called via the ppc_md.init_early function pointer.
   * At this point, the device tree has been unflattened, so we can obtain the
   * byte channel handle for stdout.
   *
   * We only support displaying of characters (putc).  We do not support
   * keyboard input.
   */
  void __init udbg_init_ehv_bc(void)
  {
  	unsigned int rx_count, tx_count;
  	unsigned int ret;

  	/* Verify the byte channel handle */
  	ret = ev_byte_channel_poll(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
  				   &rx_count, &tx_count);
  	if (ret)
  		return;
  
  	udbg_putc = ehv_bc_udbg_putc;
  	register_early_udbg_console();
  
  	udbg_printf("ehv-bc: early console using byte channel handle %u
  ",
  		    CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
  }
  
  #endif
  
  /****************************** CONSOLE DRIVER ******************************/
  
  static struct tty_driver *ehv_bc_driver;
  
  /*
   * Byte channel console sending worker function.
   *
   * For consoles, if the output buffer is full, we should just spin until it
   * clears.
   */
  static int ehv_bc_console_byte_channel_send(unsigned int handle, const char *s,
  			     unsigned int count)
  {
  	unsigned int len;
  	int ret = 0;
  
  	while (count) {
  		len = min_t(unsigned int, count, EV_BYTE_CHANNEL_MAX_BYTES);
  		do {

  			ret = local_ev_byte_channel_send(handle, &len, s);

  		} while (ret == EV_EAGAIN);
  		count -= len;
  		s += len;
  	}
  
  	return ret;
  }
  
  /*
   * write a string to the console
   *
   * This function gets called to write a string from the kernel, typically from
   * a printk().  This function spins until all data is written.
   *
   * We copy the data to a temporary buffer because we need to insert a \r in
   * front of every 
  .  It's more efficient to copy the data to the buffer than
   * it is to make multiple hcalls for each character or each newline.
   */
  static void ehv_bc_console_write(struct console *co, const char *s,
  				 unsigned int count)
  {

  	char s2[EV_BYTE_CHANNEL_MAX_BYTES];
  	unsigned int i, j = 0;
  	char c;
  
  	for (i = 0; i < count; i++) {
  		c = *s++;
  
  		if (c == '
  ')
  			s2[j++] = '\r';
  
  		s2[j++] = c;
  		if (j >= (EV_BYTE_CHANNEL_MAX_BYTES - 1)) {

  			if (ehv_bc_console_byte_channel_send(stdout_bc, s2, j))

  				return;
  			j = 0;
  		}
  	}
  
  	if (j)

  		ehv_bc_console_byte_channel_send(stdout_bc, s2, j);

  }
  
  /*
   * When /dev/console is opened, the kernel iterates the console list looking
   * for one with ->device and then calls that method. On success, it expects
   * the passed-in int* to contain the minor number to use.
   */
  static struct tty_driver *ehv_bc_console_device(struct console *co, int *index)
  {
  	*index = co->index;
  
  	return ehv_bc_driver;
  }
  
  static struct console ehv_bc_console = {
  	.name		= "ttyEHV",
  	.write		= ehv_bc_console_write,
  	.device		= ehv_bc_console_device,
  	.flags		= CON_PRINTBUFFER | CON_ENABLED,
  };
  
  /*
   * Console initialization
   *
   * This is the first function that is called after the device tree is
   * available, so here is where we determine the byte channel handle and IRQ for
   * stdout/stdin, even though that information is used by the tty and character
   * drivers.
   */
  static int __init ehv_bc_console_init(void)
  {
  	if (!find_console_handle()) {
  		pr_debug("ehv-bc: stdout is not a byte channel
  ");
  		return -ENODEV;
  	}
  
  #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
  	/* Print a friendly warning if the user chose the wrong byte channel
  	 * handle for udbg.
  	 */
  	if (stdout_bc != CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE)

  		pr_warn("ehv-bc: udbg handle %u is not the stdout handle
  ",
  			CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);

  #endif

  	/* add_preferred_console() must be called before register_console(),
  	   otherwise it won't work.  However, we don't want to enumerate all the
  	   byte channels here, either, since we only care about one. */
  
  	add_preferred_console(ehv_bc_console.name, ehv_bc_console.index, NULL);
  	register_console(&ehv_bc_console);
  
  	pr_info("ehv-bc: registered console driver for byte channel %u
  ",
  		stdout_bc);
  
  	return 0;
  }
  console_initcall(ehv_bc_console_init);
  
  /******************************** TTY DRIVER ********************************/
  
  /*

   * byte channel receive interrupt handler

   *
   * This ISR is called whenever data is available on a byte channel.
   */
  static irqreturn_t ehv_bc_tty_rx_isr(int irq, void *data)
  {
  	struct ehv_bc_data *bc = data;

  	unsigned int rx_count, tx_count, len;
  	int count;
  	char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
  	int ret;

  	/* Find out how much data needs to be read, and then ask the TTY layer
  	 * if it can handle that much.  We want to ensure that every byte we
  	 * read from the byte channel will be accepted by the TTY layer.
  	 */
  	ev_byte_channel_poll(bc->handle, &rx_count, &tx_count);

  	count = tty_buffer_request_room(&bc->port, rx_count);

  
  	/* 'count' is the maximum amount of data the TTY layer can accept at
  	 * this time.  However, during testing, I was never able to get 'count'
  	 * to be less than 'rx_count'.  I'm not sure whether I'm calling it
  	 * correctly.
  	 */
  
  	while (count > 0) {
  		len = min_t(unsigned int, count, sizeof(buffer));
  
  		/* Read some data from the byte channel.  This function will
  		 * never return more than EV_BYTE_CHANNEL_MAX_BYTES bytes.
  		 */
  		ev_byte_channel_receive(bc->handle, &len, buffer);
  
  		/* 'len' is now the amount of data that's been received. 'len'
  		 * can't be zero, and most likely it's equal to one.
  		 */
  
  		/* Pass the received data to the tty layer. */

  		ret = tty_insert_flip_string(&bc->port, buffer, len);

  
  		/* 'ret' is the number of bytes that the TTY layer accepted.
  		 * If it's not equal to 'len', then it means the buffer is
  		 * full, which should never happen.  If it does happen, we can
  		 * exit gracefully, but we drop the last 'len - ret' characters
  		 * that we read from the byte channel.
  		 */
  		if (ret != len)
  			break;
  
  		count -= len;
  	}
  
  	/* Tell the tty layer that we're done. */

  	tty_flip_buffer_push(&bc->port);

  
  	return IRQ_HANDLED;
  }
  
  /*
   * dequeue the transmit buffer to the hypervisor
   *
   * This function, which can be called in interrupt context, dequeues as much
   * data as possible from the transmit buffer to the byte channel.
   */
  static void ehv_bc_tx_dequeue(struct ehv_bc_data *bc)
  {
  	unsigned int count;
  	unsigned int len, ret;
  	unsigned long flags;
  
  	do {
  		spin_lock_irqsave(&bc->lock, flags);
  		len = min_t(unsigned int,
  			    CIRC_CNT_TO_END(bc->head, bc->tail, BUF_SIZE),
  			    EV_BYTE_CHANNEL_MAX_BYTES);

  		ret = local_ev_byte_channel_send(bc->handle, &len, bc->buf + bc->tail);

  
  		/* 'len' is valid only if the return code is 0 or EV_EAGAIN */
  		if (!ret || (ret == EV_EAGAIN))
  			bc->tail = (bc->tail + len) & (BUF_SIZE - 1);
  
  		count = CIRC_CNT(bc->head, bc->tail, BUF_SIZE);
  		spin_unlock_irqrestore(&bc->lock, flags);
  	} while (count && !ret);
  
  	spin_lock_irqsave(&bc->lock, flags);
  	if (CIRC_CNT(bc->head, bc->tail, BUF_SIZE))
  		/*
  		 * If we haven't emptied the buffer, then enable the TX IRQ.
  		 * We'll get an interrupt when there's more room in the
  		 * hypervisor's output buffer.
  		 */
  		enable_tx_interrupt(bc);
  	else
  		disable_tx_interrupt(bc);
  	spin_unlock_irqrestore(&bc->lock, flags);
  }
  
  /*

   * byte channel transmit interrupt handler

   *
   * This ISR is called whenever space becomes available for transmitting
   * characters on a byte channel.
   */
  static irqreturn_t ehv_bc_tty_tx_isr(int irq, void *data)
  {
  	struct ehv_bc_data *bc = data;

  
  	ehv_bc_tx_dequeue(bc);

  	tty_port_tty_wakeup(&bc->port);

  
  	return IRQ_HANDLED;
  }
  
  /*
   * This function is called when the tty layer has data for us send.  We store
   * the data first in a circular buffer, and then dequeue as much of that data
   * as possible.
   *
   * We don't need to worry about whether there is enough room in the buffer for
   * all the data.  The purpose of ehv_bc_tty_write_room() is to tell the tty
   * layer how much data it can safely send to us.  We guarantee that
   * ehv_bc_tty_write_room() will never lie, so the tty layer will never send us
   * too much data.
   */
  static int ehv_bc_tty_write(struct tty_struct *ttys, const unsigned char *s,
  			    int count)
  {
  	struct ehv_bc_data *bc = ttys->driver_data;
  	unsigned long flags;
  	unsigned int len;
  	unsigned int written = 0;
  
  	while (1) {
  		spin_lock_irqsave(&bc->lock, flags);
  		len = CIRC_SPACE_TO_END(bc->head, bc->tail, BUF_SIZE);
  		if (count < len)
  			len = count;
  		if (len) {
  			memcpy(bc->buf + bc->head, s, len);
  			bc->head = (bc->head + len) & (BUF_SIZE - 1);
  		}
  		spin_unlock_irqrestore(&bc->lock, flags);
  		if (!len)
  			break;
  
  		s += len;
  		count -= len;
  		written += len;
  	}
  
  	ehv_bc_tx_dequeue(bc);
  
  	return written;
  }
  
  /*
   * This function can be called multiple times for a given tty_struct, which is
   * why we initialize bc->ttys in ehv_bc_tty_port_activate() instead.
   *
   * The tty layer will still call this function even if the device was not
   * registered (i.e. tty_register_device() was not called).  This happens
   * because tty_register_device() is optional and some legacy drivers don't
   * use it.  So we need to check for that.
   */
  static int ehv_bc_tty_open(struct tty_struct *ttys, struct file *filp)
  {
  	struct ehv_bc_data *bc = &bcs[ttys->index];
  
  	if (!bc->dev)
  		return -ENODEV;
  
  	return tty_port_open(&bc->port, ttys, filp);
  }
  
  /*
   * Amazingly, if ehv_bc_tty_open() returns an error code, the tty layer will
   * still call this function to close the tty device.  So we can't assume that
   * the tty port has been initialized.
   */
  static void ehv_bc_tty_close(struct tty_struct *ttys, struct file *filp)
  {
  	struct ehv_bc_data *bc = &bcs[ttys->index];
  
  	if (bc->dev)
  		tty_port_close(&bc->port, ttys, filp);
  }
  
  /*
   * Return the amount of space in the output buffer
   *
   * This is actually a contract between the driver and the tty layer outlining
   * how much write room the driver can guarantee will be sent OR BUFFERED.  This
   * driver MUST honor the return value.
   */
  static int ehv_bc_tty_write_room(struct tty_struct *ttys)
  {
  	struct ehv_bc_data *bc = ttys->driver_data;
  	unsigned long flags;
  	int count;
  
  	spin_lock_irqsave(&bc->lock, flags);
  	count = CIRC_SPACE(bc->head, bc->tail, BUF_SIZE);
  	spin_unlock_irqrestore(&bc->lock, flags);
  
  	return count;
  }
  
  /*
   * Stop sending data to the tty layer
   *
   * This function is called when the tty layer's input buffers are getting full,
   * so the driver should stop sending it data.  The easiest way to do this is to
   * disable the RX IRQ, which will prevent ehv_bc_tty_rx_isr() from being
   * called.
   *
   * The hypervisor will continue to queue up any incoming data.  If there is any
   * data in the queue when the RX interrupt is enabled, we'll immediately get an
   * RX interrupt.
   */
  static void ehv_bc_tty_throttle(struct tty_struct *ttys)
  {
  	struct ehv_bc_data *bc = ttys->driver_data;
  
  	disable_irq(bc->rx_irq);
  }
  
  /*
   * Resume sending data to the tty layer
   *
   * This function is called after previously calling ehv_bc_tty_throttle().  The
   * tty layer's input buffers now have more room, so the driver can resume
   * sending it data.
   */
  static void ehv_bc_tty_unthrottle(struct tty_struct *ttys)
  {
  	struct ehv_bc_data *bc = ttys->driver_data;
  
  	/* If there is any data in the queue when the RX interrupt is enabled,
  	 * we'll immediately get an RX interrupt.
  	 */
  	enable_irq(bc->rx_irq);
  }
  
  static void ehv_bc_tty_hangup(struct tty_struct *ttys)
  {
  	struct ehv_bc_data *bc = ttys->driver_data;
  
  	ehv_bc_tx_dequeue(bc);
  	tty_port_hangup(&bc->port);
  }
  
  /*
   * TTY driver operations
   *
   * If we could ask the hypervisor how much data is still in the TX buffer, or
   * at least how big the TX buffers are, then we could implement the
   * .wait_until_sent and .chars_in_buffer functions.
   */
  static const struct tty_operations ehv_bc_ops = {
  	.open		= ehv_bc_tty_open,
  	.close		= ehv_bc_tty_close,
  	.write		= ehv_bc_tty_write,
  	.write_room	= ehv_bc_tty_write_room,
  	.throttle	= ehv_bc_tty_throttle,
  	.unthrottle	= ehv_bc_tty_unthrottle,
  	.hangup		= ehv_bc_tty_hangup,
  };
  
  /*
   * initialize the TTY port
   *
   * This function will only be called once, no matter how many times
   * ehv_bc_tty_open() is called.  That's why we register the ISR here, and also
   * why we initialize tty_struct-related variables here.
   */
  static int ehv_bc_tty_port_activate(struct tty_port *port,
  				    struct tty_struct *ttys)
  {
  	struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
  	int ret;
  
  	ttys->driver_data = bc;
  
  	ret = request_irq(bc->rx_irq, ehv_bc_tty_rx_isr, 0, "ehv-bc", bc);
  	if (ret < 0) {
  		dev_err(bc->dev, "could not request rx irq %u (ret=%i)
  ",
  		       bc->rx_irq, ret);
  		return ret;
  	}
  
  	/* request_irq also enables the IRQ */
  	bc->tx_irq_enabled = 1;
  
  	ret = request_irq(bc->tx_irq, ehv_bc_tty_tx_isr, 0, "ehv-bc", bc);
  	if (ret < 0) {
  		dev_err(bc->dev, "could not request tx irq %u (ret=%i)
  ",
  		       bc->tx_irq, ret);
  		free_irq(bc->rx_irq, bc);
  		return ret;
  	}
  
  	/* The TX IRQ is enabled only when we can't write all the data to the
  	 * byte channel at once, so by default it's disabled.
  	 */
  	disable_tx_interrupt(bc);
  
  	return 0;
  }
  
  static void ehv_bc_tty_port_shutdown(struct tty_port *port)
  {
  	struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
  
  	free_irq(bc->tx_irq, bc);
  	free_irq(bc->rx_irq, bc);
  }
  
  static const struct tty_port_operations ehv_bc_tty_port_ops = {
  	.activate = ehv_bc_tty_port_activate,
  	.shutdown = ehv_bc_tty_port_shutdown,
  };

  static int ehv_bc_tty_probe(struct platform_device *pdev)

  {
  	struct device_node *np = pdev->dev.of_node;
  	struct ehv_bc_data *bc;
  	const uint32_t *iprop;
  	unsigned int handle;
  	int ret;
  	static unsigned int index = 1;
  	unsigned int i;
  
  	iprop = of_get_property(np, "hv-handle", NULL);
  	if (!iprop) {

  		dev_err(&pdev->dev, "no 'hv-handle' property in %pOFn node
  ",
  			np);

  		return -ENODEV;
  	}
  
  	/* We already told the console layer that the index for the console
  	 * device is zero, so we need to make sure that we use that index when
  	 * we probe the console byte channel node.
  	 */
  	handle = be32_to_cpu(*iprop);
  	i = (handle == stdout_bc) ? 0 : index++;
  	bc = &bcs[i];
  
  	bc->handle = handle;
  	bc->head = 0;
  	bc->tail = 0;
  	spin_lock_init(&bc->lock);
  
  	bc->rx_irq = irq_of_parse_and_map(np, 0);
  	bc->tx_irq = irq_of_parse_and_map(np, 1);
  	if ((bc->rx_irq == NO_IRQ) || (bc->tx_irq == NO_IRQ)) {

  		dev_err(&pdev->dev, "no 'interrupts' property in %pOFn node
  ",
  			np);

  		ret = -ENODEV;
  		goto error;
  	}

  	tty_port_init(&bc->port);
  	bc->port.ops = &ehv_bc_tty_port_ops;
  
  	bc->dev = tty_port_register_device(&bc->port, ehv_bc_driver, i,
  			&pdev->dev);

  	if (IS_ERR(bc->dev)) {
  		ret = PTR_ERR(bc->dev);
  		dev_err(&pdev->dev, "could not register tty (ret=%i)
  ", ret);
  		goto error;
  	}

  	dev_set_drvdata(&pdev->dev, bc);
  
  	dev_info(&pdev->dev, "registered /dev/%s%u for byte channel %u
  ",
  		ehv_bc_driver->name, i, bc->handle);
  
  	return 0;
  
  error:

  	tty_port_destroy(&bc->port);

  	irq_dispose_mapping(bc->tx_irq);
  	irq_dispose_mapping(bc->rx_irq);
  
  	memset(bc, 0, sizeof(struct ehv_bc_data));
  	return ret;
  }

  static const struct of_device_id ehv_bc_tty_of_ids[] = {
  	{ .compatible = "epapr,hv-byte-channel" },
  	{}
  };
  
  static struct platform_driver ehv_bc_tty_driver = {
  	.driver = {

  		.name = "ehv-bc",
  		.of_match_table = ehv_bc_tty_of_ids,

  		.suppress_bind_attrs = true,

  	},
  	.probe		= ehv_bc_tty_probe,

  };
  
  /**
   * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
   *

   * This function is called when this driver is loaded.

   */
  static int __init ehv_bc_init(void)
  {
  	struct device_node *np;
  	unsigned int count = 0; /* Number of elements in bcs[] */
  	int ret;
  
  	pr_info("ePAPR hypervisor byte channel driver
  ");
  
  	/* Count the number of byte channels */
  	for_each_compatible_node(np, NULL, "epapr,hv-byte-channel")
  		count++;
  
  	if (!count)
  		return -ENODEV;
  
  	/* The array index of an element in bcs[] is the same as the tty index
  	 * for that element.  If you know the address of an element in the
  	 * array, then you can use pointer math (e.g. "bc - bcs") to get its
  	 * tty index.
  	 */

  	bcs = kcalloc(count, sizeof(struct ehv_bc_data), GFP_KERNEL);

  	if (!bcs)
  		return -ENOMEM;
  
  	ehv_bc_driver = alloc_tty_driver(count);
  	if (!ehv_bc_driver) {
  		ret = -ENOMEM;

  		goto err_free_bcs;

  	}

  	ehv_bc_driver->driver_name = "ehv-bc";
  	ehv_bc_driver->name = ehv_bc_console.name;
  	ehv_bc_driver->type = TTY_DRIVER_TYPE_CONSOLE;
  	ehv_bc_driver->subtype = SYSTEM_TYPE_CONSOLE;
  	ehv_bc_driver->init_termios = tty_std_termios;
  	ehv_bc_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
  	tty_set_operations(ehv_bc_driver, &ehv_bc_ops);
  
  	ret = tty_register_driver(ehv_bc_driver);
  	if (ret) {
  		pr_err("ehv-bc: could not register tty driver (ret=%i)
  ", ret);

  		goto err_put_tty_driver;

  	}
  
  	ret = platform_driver_register(&ehv_bc_tty_driver);
  	if (ret) {
  		pr_err("ehv-bc: could not register platform driver (ret=%i)
  ",
  		       ret);

  		goto err_deregister_tty_driver;

  	}
  
  	return 0;

  err_deregister_tty_driver:
  	tty_unregister_driver(ehv_bc_driver);
  err_put_tty_driver:
  	put_tty_driver(ehv_bc_driver);
  err_free_bcs:

  	kfree(bcs);
  
  	return ret;
  }

  device_initcall(ehv_bc_init);