OSCL-LXR linux-6.0.1/​drivers/​tty/​ehv_bytechan.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // 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\n", 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\n",
                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 == '\n')
         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\n",
             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 \n.  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 == '\n')
             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\n");
         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\n",
             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\n",
         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 unsigned int ehv_bc_tty_write_room(struct tty_struct *ttys)
 {
     struct ehv_bc_data *bc = ttys->driver_data;
     unsigned long flags;
     unsigned 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)\n",
                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)\n",
                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\n",
             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\n",
             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)\n", ret);
         goto error;
     }
 
     dev_set_drvdata(&pdev->dev, bc);
 
     dev_info(&pdev->dev, "registered /dev/%s%u for byte channel %u\n",
         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 tty_driver *driver;
     struct device_node *np;
     unsigned int count = 0; /* Number of elements in bcs[] */
     int ret;
 
     pr_info("ePAPR hypervisor byte channel driver\n");
 
     /* 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;
 
     driver = tty_alloc_driver(count, TTY_DRIVER_REAL_RAW |
             TTY_DRIVER_DYNAMIC_DEV);
     if (IS_ERR(driver)) {
         ret = PTR_ERR(driver);
         goto err_free_bcs;
     }
 
     driver->driver_name = "ehv-bc";
     driver->name = ehv_bc_console.name;
     driver->type = TTY_DRIVER_TYPE_CONSOLE;
     driver->subtype = SYSTEM_TYPE_CONSOLE;
     driver->init_termios = tty_std_termios;
     tty_set_operations(driver, &ehv_bc_ops);
 
     ret = tty_register_driver(driver);
     if (ret) {
         pr_err("ehv-bc: could not register tty driver (ret=%i)\n", ret);
         goto err_tty_driver_kref_put;
     }
 
     ehv_bc_driver = driver;
 
     ret = platform_driver_register(&ehv_bc_tty_driver);
     if (ret) {
         pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
                ret);
         goto err_deregister_tty_driver;
     }
 
     return 0;
 
 err_deregister_tty_driver:
     ehv_bc_driver = NULL;
     tty_unregister_driver(driver);
 err_tty_driver_kref_put:
     tty_driver_kref_put(driver);
 err_free_bcs:
     kfree(bcs);
 
     return ret;
 }
 device_initcall(ehv_bc_init);

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