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Linux/drivers/tty/ehv_bytechan.c

  1 /* ePAPR hypervisor byte channel device driver
  2  *
  3  * Copyright 2009-2011 Freescale Semiconductor, Inc.
  4  *
  5  * Author: Timur Tabi <timur@freescale.com>
  6  *
  7  * This file is licensed under the terms of the GNU General Public License
  8  * version 2.  This program is licensed "as is" without any warranty of any
  9  * kind, whether express or implied.
 10  *
 11  * This driver support three distinct interfaces, all of which are related to
 12  * ePAPR hypervisor byte channels.
 13  *
 14  * 1) An early-console (udbg) driver.  This provides early console output
 15  * through a byte channel.  The byte channel handle must be specified in a
 16  * Kconfig option.
 17  *
 18  * 2) A normal console driver.  Output is sent to the byte channel designated
 19  * for stdout in the device tree.  The console driver is for handling kernel
 20  * printk calls.
 21  *
 22  * 3) A tty driver, which is used to handle user-space input and output.  The
 23  * byte channel used for the console is designated as the default tty.
 24  */
 25 
 26 #include <linux/init.h>
 27 #include <linux/slab.h>
 28 #include <linux/err.h>
 29 #include <linux/interrupt.h>
 30 #include <linux/fs.h>
 31 #include <linux/poll.h>
 32 #include <asm/epapr_hcalls.h>
 33 #include <linux/of.h>
 34 #include <linux/of_irq.h>
 35 #include <linux/platform_device.h>
 36 #include <linux/cdev.h>
 37 #include <linux/console.h>
 38 #include <linux/tty.h>
 39 #include <linux/tty_flip.h>
 40 #include <linux/circ_buf.h>
 41 #include <asm/udbg.h>
 42 
 43 /* The size of the transmit circular buffer.  This must be a power of two. */
 44 #define BUF_SIZE        2048
 45 
 46 /* Per-byte channel private data */
 47 struct ehv_bc_data {
 48         struct device *dev;
 49         struct tty_port port;
 50         uint32_t handle;
 51         unsigned int rx_irq;
 52         unsigned int tx_irq;
 53 
 54         spinlock_t lock;        /* lock for transmit buffer */
 55         unsigned char buf[BUF_SIZE];    /* transmit circular buffer */
 56         unsigned int head;      /* circular buffer head */
 57         unsigned int tail;      /* circular buffer tail */
 58 
 59         int tx_irq_enabled;     /* true == TX interrupt is enabled */
 60 };
 61 
 62 /* Array of byte channel objects */
 63 static struct ehv_bc_data *bcs;
 64 
 65 /* Byte channel handle for stdout (and stdin), taken from device tree */
 66 static unsigned int stdout_bc;
 67 
 68 /* Virtual IRQ for the byte channel handle for stdin, taken from device tree */
 69 static unsigned int stdout_irq;
 70 
 71 /**************************** SUPPORT FUNCTIONS ****************************/
 72 
 73 /*
 74  * Enable the transmit interrupt
 75  *
 76  * Unlike a serial device, byte channels have no mechanism for disabling their
 77  * own receive or transmit interrupts.  To emulate that feature, we toggle
 78  * the IRQ in the kernel.
 79  *
 80  * We cannot just blindly call enable_irq() or disable_irq(), because these
 81  * calls are reference counted.  This means that we cannot call enable_irq()
 82  * if interrupts are already enabled.  This can happen in two situations:
 83  *
 84  * 1. The tty layer makes two back-to-back calls to ehv_bc_tty_write()
 85  * 2. A transmit interrupt occurs while executing ehv_bc_tx_dequeue()
 86  *
 87  * To work around this, we keep a flag to tell us if the IRQ is enabled or not.
 88  */
 89 static void enable_tx_interrupt(struct ehv_bc_data *bc)
 90 {
 91         if (!bc->tx_irq_enabled) {
 92                 enable_irq(bc->tx_irq);
 93                 bc->tx_irq_enabled = 1;
 94         }
 95 }
 96 
 97 static void disable_tx_interrupt(struct ehv_bc_data *bc)
 98 {
 99         if (bc->tx_irq_enabled) {
100                 disable_irq_nosync(bc->tx_irq);
101                 bc->tx_irq_enabled = 0;
102         }
103 }
104 
105 /*
106  * find the byte channel handle to use for the console
107  *
108  * The byte channel to be used for the console is specified via a "stdout"
109  * property in the /chosen node.
110  */
111 static int find_console_handle(void)
112 {
113         struct device_node *np = of_stdout;
114         const uint32_t *iprop;
115 
116         /* We don't care what the aliased node is actually called.  We only
117          * care if it's compatible with "epapr,hv-byte-channel", because that
118          * indicates that it's a byte channel node.
119          */
120         if (!np || !of_device_is_compatible(np, "epapr,hv-byte-channel"))
121                 return 0;
122 
123         stdout_irq = irq_of_parse_and_map(np, 0);
124         if (stdout_irq == NO_IRQ) {
125                 pr_err("ehv-bc: no 'interrupts' property in %s node\n", np->full_name);
126                 return 0;
127         }
128 
129         /*
130          * The 'hv-handle' property contains the handle for this byte channel.
131          */
132         iprop = of_get_property(np, "hv-handle", NULL);
133         if (!iprop) {
134                 pr_err("ehv-bc: no 'hv-handle' property in %s node\n",
135                        np->name);
136                 return 0;
137         }
138         stdout_bc = be32_to_cpu(*iprop);
139         return 1;
140 }
141 
142 /*************************** EARLY CONSOLE DRIVER ***************************/
143 
144 #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
145 
146 /*
147  * send a byte to a byte channel, wait if necessary
148  *
149  * This function sends a byte to a byte channel, and it waits and
150  * retries if the byte channel is full.  It returns if the character
151  * has been sent, or if some error has occurred.
152  *
153  */
154 static void byte_channel_spin_send(const char data)
155 {
156         int ret, count;
157 
158         do {
159                 count = 1;
160                 ret = ev_byte_channel_send(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
161                                            &count, &data);
162         } while (ret == EV_EAGAIN);
163 }
164 
165 /*
166  * The udbg subsystem calls this function to display a single character.
167  * We convert CR to a CR/LF.
168  */
169 static void ehv_bc_udbg_putc(char c)
170 {
171         if (c == '\n')
172                 byte_channel_spin_send('\r');
173 
174         byte_channel_spin_send(c);
175 }
176 
177 /*
178  * early console initialization
179  *
180  * PowerPC kernels support an early printk console, also known as udbg.
181  * This function must be called via the ppc_md.init_early function pointer.
182  * At this point, the device tree has been unflattened, so we can obtain the
183  * byte channel handle for stdout.
184  *
185  * We only support displaying of characters (putc).  We do not support
186  * keyboard input.
187  */
188 void __init udbg_init_ehv_bc(void)
189 {
190         unsigned int rx_count, tx_count;
191         unsigned int ret;
192 
193         /* Verify the byte channel handle */
194         ret = ev_byte_channel_poll(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
195                                    &rx_count, &tx_count);
196         if (ret)
197                 return;
198 
199         udbg_putc = ehv_bc_udbg_putc;
200         register_early_udbg_console();
201 
202         udbg_printf("ehv-bc: early console using byte channel handle %u\n",
203                     CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
204 }
205 
206 #endif
207 
208 /****************************** CONSOLE DRIVER ******************************/
209 
210 static struct tty_driver *ehv_bc_driver;
211 
212 /*
213  * Byte channel console sending worker function.
214  *
215  * For consoles, if the output buffer is full, we should just spin until it
216  * clears.
217  */
218 static int ehv_bc_console_byte_channel_send(unsigned int handle, const char *s,
219                              unsigned int count)
220 {
221         unsigned int len;
222         int ret = 0;
223 
224         while (count) {
225                 len = min_t(unsigned int, count, EV_BYTE_CHANNEL_MAX_BYTES);
226                 do {
227                         ret = ev_byte_channel_send(handle, &len, s);
228                 } while (ret == EV_EAGAIN);
229                 count -= len;
230                 s += len;
231         }
232 
233         return ret;
234 }
235 
236 /*
237  * write a string to the console
238  *
239  * This function gets called to write a string from the kernel, typically from
240  * a printk().  This function spins until all data is written.
241  *
242  * We copy the data to a temporary buffer because we need to insert a \r in
243  * front of every \n.  It's more efficient to copy the data to the buffer than
244  * it is to make multiple hcalls for each character or each newline.
245  */
246 static void ehv_bc_console_write(struct console *co, const char *s,
247                                  unsigned int count)
248 {
249         char s2[EV_BYTE_CHANNEL_MAX_BYTES];
250         unsigned int i, j = 0;
251         char c;
252 
253         for (i = 0; i < count; i++) {
254                 c = *s++;
255 
256                 if (c == '\n')
257                         s2[j++] = '\r';
258 
259                 s2[j++] = c;
260                 if (j >= (EV_BYTE_CHANNEL_MAX_BYTES - 1)) {
261                         if (ehv_bc_console_byte_channel_send(stdout_bc, s2, j))
262                                 return;
263                         j = 0;
264                 }
265         }
266 
267         if (j)
268                 ehv_bc_console_byte_channel_send(stdout_bc, s2, j);
269 }
270 
271 /*
272  * When /dev/console is opened, the kernel iterates the console list looking
273  * for one with ->device and then calls that method. On success, it expects
274  * the passed-in int* to contain the minor number to use.
275  */
276 static struct tty_driver *ehv_bc_console_device(struct console *co, int *index)
277 {
278         *index = co->index;
279 
280         return ehv_bc_driver;
281 }
282 
283 static struct console ehv_bc_console = {
284         .name           = "ttyEHV",
285         .write          = ehv_bc_console_write,
286         .device         = ehv_bc_console_device,
287         .flags          = CON_PRINTBUFFER | CON_ENABLED,
288 };
289 
290 /*
291  * Console initialization
292  *
293  * This is the first function that is called after the device tree is
294  * available, so here is where we determine the byte channel handle and IRQ for
295  * stdout/stdin, even though that information is used by the tty and character
296  * drivers.
297  */
298 static int __init ehv_bc_console_init(void)
299 {
300         if (!find_console_handle()) {
301                 pr_debug("ehv-bc: stdout is not a byte channel\n");
302                 return -ENODEV;
303         }
304 
305 #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
306         /* Print a friendly warning if the user chose the wrong byte channel
307          * handle for udbg.
308          */
309         if (stdout_bc != CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE)
310                 pr_warn("ehv-bc: udbg handle %u is not the stdout handle\n",
311                         CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
312 #endif
313 
314         /* add_preferred_console() must be called before register_console(),
315            otherwise it won't work.  However, we don't want to enumerate all the
316            byte channels here, either, since we only care about one. */
317 
318         add_preferred_console(ehv_bc_console.name, ehv_bc_console.index, NULL);
319         register_console(&ehv_bc_console);
320 
321         pr_info("ehv-bc: registered console driver for byte channel %u\n",
322                 stdout_bc);
323 
324         return 0;
325 }
326 console_initcall(ehv_bc_console_init);
327 
328 /******************************** TTY DRIVER ********************************/
329 
330 /*
331  * byte channel receive interupt handler
332  *
333  * This ISR is called whenever data is available on a byte channel.
334  */
335 static irqreturn_t ehv_bc_tty_rx_isr(int irq, void *data)
336 {
337         struct ehv_bc_data *bc = data;
338         unsigned int rx_count, tx_count, len;
339         int count;
340         char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
341         int ret;
342 
343         /* Find out how much data needs to be read, and then ask the TTY layer
344          * if it can handle that much.  We want to ensure that every byte we
345          * read from the byte channel will be accepted by the TTY layer.
346          */
347         ev_byte_channel_poll(bc->handle, &rx_count, &tx_count);
348         count = tty_buffer_request_room(&bc->port, rx_count);
349 
350         /* 'count' is the maximum amount of data the TTY layer can accept at
351          * this time.  However, during testing, I was never able to get 'count'
352          * to be less than 'rx_count'.  I'm not sure whether I'm calling it
353          * correctly.
354          */
355 
356         while (count > 0) {
357                 len = min_t(unsigned int, count, sizeof(buffer));
358 
359                 /* Read some data from the byte channel.  This function will
360                  * never return more than EV_BYTE_CHANNEL_MAX_BYTES bytes.
361                  */
362                 ev_byte_channel_receive(bc->handle, &len, buffer);
363 
364                 /* 'len' is now the amount of data that's been received. 'len'
365                  * can't be zero, and most likely it's equal to one.
366                  */
367 
368                 /* Pass the received data to the tty layer. */
369                 ret = tty_insert_flip_string(&bc->port, buffer, len);
370 
371                 /* 'ret' is the number of bytes that the TTY layer accepted.
372                  * If it's not equal to 'len', then it means the buffer is
373                  * full, which should never happen.  If it does happen, we can
374                  * exit gracefully, but we drop the last 'len - ret' characters
375                  * that we read from the byte channel.
376                  */
377                 if (ret != len)
378                         break;
379 
380                 count -= len;
381         }
382 
383         /* Tell the tty layer that we're done. */
384         tty_flip_buffer_push(&bc->port);
385 
386         return IRQ_HANDLED;
387 }
388 
389 /*
390  * dequeue the transmit buffer to the hypervisor
391  *
392  * This function, which can be called in interrupt context, dequeues as much
393  * data as possible from the transmit buffer to the byte channel.
394  */
395 static void ehv_bc_tx_dequeue(struct ehv_bc_data *bc)
396 {
397         unsigned int count;
398         unsigned int len, ret;
399         unsigned long flags;
400 
401         do {
402                 spin_lock_irqsave(&bc->lock, flags);
403                 len = min_t(unsigned int,
404                             CIRC_CNT_TO_END(bc->head, bc->tail, BUF_SIZE),
405                             EV_BYTE_CHANNEL_MAX_BYTES);
406 
407                 ret = ev_byte_channel_send(bc->handle, &len, bc->buf + bc->tail);
408 
409                 /* 'len' is valid only if the return code is 0 or EV_EAGAIN */
410                 if (!ret || (ret == EV_EAGAIN))
411                         bc->tail = (bc->tail + len) & (BUF_SIZE - 1);
412 
413                 count = CIRC_CNT(bc->head, bc->tail, BUF_SIZE);
414                 spin_unlock_irqrestore(&bc->lock, flags);
415         } while (count && !ret);
416 
417         spin_lock_irqsave(&bc->lock, flags);
418         if (CIRC_CNT(bc->head, bc->tail, BUF_SIZE))
419                 /*
420                  * If we haven't emptied the buffer, then enable the TX IRQ.
421                  * We'll get an interrupt when there's more room in the
422                  * hypervisor's output buffer.
423                  */
424                 enable_tx_interrupt(bc);
425         else
426                 disable_tx_interrupt(bc);
427         spin_unlock_irqrestore(&bc->lock, flags);
428 }
429 
430 /*
431  * byte channel transmit interupt handler
432  *
433  * This ISR is called whenever space becomes available for transmitting
434  * characters on a byte channel.
435  */
436 static irqreturn_t ehv_bc_tty_tx_isr(int irq, void *data)
437 {
438         struct ehv_bc_data *bc = data;
439 
440         ehv_bc_tx_dequeue(bc);
441         tty_port_tty_wakeup(&bc->port);
442 
443         return IRQ_HANDLED;
444 }
445 
446 /*
447  * This function is called when the tty layer has data for us send.  We store
448  * the data first in a circular buffer, and then dequeue as much of that data
449  * as possible.
450  *
451  * We don't need to worry about whether there is enough room in the buffer for
452  * all the data.  The purpose of ehv_bc_tty_write_room() is to tell the tty
453  * layer how much data it can safely send to us.  We guarantee that
454  * ehv_bc_tty_write_room() will never lie, so the tty layer will never send us
455  * too much data.
456  */
457 static int ehv_bc_tty_write(struct tty_struct *ttys, const unsigned char *s,
458                             int count)
459 {
460         struct ehv_bc_data *bc = ttys->driver_data;
461         unsigned long flags;
462         unsigned int len;
463         unsigned int written = 0;
464 
465         while (1) {
466                 spin_lock_irqsave(&bc->lock, flags);
467                 len = CIRC_SPACE_TO_END(bc->head, bc->tail, BUF_SIZE);
468                 if (count < len)
469                         len = count;
470                 if (len) {
471                         memcpy(bc->buf + bc->head, s, len);
472                         bc->head = (bc->head + len) & (BUF_SIZE - 1);
473                 }
474                 spin_unlock_irqrestore(&bc->lock, flags);
475                 if (!len)
476                         break;
477 
478                 s += len;
479                 count -= len;
480                 written += len;
481         }
482 
483         ehv_bc_tx_dequeue(bc);
484 
485         return written;
486 }
487 
488 /*
489  * This function can be called multiple times for a given tty_struct, which is
490  * why we initialize bc->ttys in ehv_bc_tty_port_activate() instead.
491  *
492  * The tty layer will still call this function even if the device was not
493  * registered (i.e. tty_register_device() was not called).  This happens
494  * because tty_register_device() is optional and some legacy drivers don't
495  * use it.  So we need to check for that.
496  */
497 static int ehv_bc_tty_open(struct tty_struct *ttys, struct file *filp)
498 {
499         struct ehv_bc_data *bc = &bcs[ttys->index];
500 
501         if (!bc->dev)
502                 return -ENODEV;
503 
504         return tty_port_open(&bc->port, ttys, filp);
505 }
506 
507 /*
508  * Amazingly, if ehv_bc_tty_open() returns an error code, the tty layer will
509  * still call this function to close the tty device.  So we can't assume that
510  * the tty port has been initialized.
511  */
512 static void ehv_bc_tty_close(struct tty_struct *ttys, struct file *filp)
513 {
514         struct ehv_bc_data *bc = &bcs[ttys->index];
515 
516         if (bc->dev)
517                 tty_port_close(&bc->port, ttys, filp);
518 }
519 
520 /*
521  * Return the amount of space in the output buffer
522  *
523  * This is actually a contract between the driver and the tty layer outlining
524  * how much write room the driver can guarantee will be sent OR BUFFERED.  This
525  * driver MUST honor the return value.
526  */
527 static int ehv_bc_tty_write_room(struct tty_struct *ttys)
528 {
529         struct ehv_bc_data *bc = ttys->driver_data;
530         unsigned long flags;
531         int count;
532 
533         spin_lock_irqsave(&bc->lock, flags);
534         count = CIRC_SPACE(bc->head, bc->tail, BUF_SIZE);
535         spin_unlock_irqrestore(&bc->lock, flags);
536 
537         return count;
538 }
539 
540 /*
541  * Stop sending data to the tty layer
542  *
543  * This function is called when the tty layer's input buffers are getting full,
544  * so the driver should stop sending it data.  The easiest way to do this is to
545  * disable the RX IRQ, which will prevent ehv_bc_tty_rx_isr() from being
546  * called.
547  *
548  * The hypervisor will continue to queue up any incoming data.  If there is any
549  * data in the queue when the RX interrupt is enabled, we'll immediately get an
550  * RX interrupt.
551  */
552 static void ehv_bc_tty_throttle(struct tty_struct *ttys)
553 {
554         struct ehv_bc_data *bc = ttys->driver_data;
555 
556         disable_irq(bc->rx_irq);
557 }
558 
559 /*
560  * Resume sending data to the tty layer
561  *
562  * This function is called after previously calling ehv_bc_tty_throttle().  The
563  * tty layer's input buffers now have more room, so the driver can resume
564  * sending it data.
565  */
566 static void ehv_bc_tty_unthrottle(struct tty_struct *ttys)
567 {
568         struct ehv_bc_data *bc = ttys->driver_data;
569 
570         /* If there is any data in the queue when the RX interrupt is enabled,
571          * we'll immediately get an RX interrupt.
572          */
573         enable_irq(bc->rx_irq);
574 }
575 
576 static void ehv_bc_tty_hangup(struct tty_struct *ttys)
577 {
578         struct ehv_bc_data *bc = ttys->driver_data;
579 
580         ehv_bc_tx_dequeue(bc);
581         tty_port_hangup(&bc->port);
582 }
583 
584 /*
585  * TTY driver operations
586  *
587  * If we could ask the hypervisor how much data is still in the TX buffer, or
588  * at least how big the TX buffers are, then we could implement the
589  * .wait_until_sent and .chars_in_buffer functions.
590  */
591 static const struct tty_operations ehv_bc_ops = {
592         .open           = ehv_bc_tty_open,
593         .close          = ehv_bc_tty_close,
594         .write          = ehv_bc_tty_write,
595         .write_room     = ehv_bc_tty_write_room,
596         .throttle       = ehv_bc_tty_throttle,
597         .unthrottle     = ehv_bc_tty_unthrottle,
598         .hangup         = ehv_bc_tty_hangup,
599 };
600 
601 /*
602  * initialize the TTY port
603  *
604  * This function will only be called once, no matter how many times
605  * ehv_bc_tty_open() is called.  That's why we register the ISR here, and also
606  * why we initialize tty_struct-related variables here.
607  */
608 static int ehv_bc_tty_port_activate(struct tty_port *port,
609                                     struct tty_struct *ttys)
610 {
611         struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
612         int ret;
613 
614         ttys->driver_data = bc;
615 
616         ret = request_irq(bc->rx_irq, ehv_bc_tty_rx_isr, 0, "ehv-bc", bc);
617         if (ret < 0) {
618                 dev_err(bc->dev, "could not request rx irq %u (ret=%i)\n",
619                        bc->rx_irq, ret);
620                 return ret;
621         }
622 
623         /* request_irq also enables the IRQ */
624         bc->tx_irq_enabled = 1;
625 
626         ret = request_irq(bc->tx_irq, ehv_bc_tty_tx_isr, 0, "ehv-bc", bc);
627         if (ret < 0) {
628                 dev_err(bc->dev, "could not request tx irq %u (ret=%i)\n",
629                        bc->tx_irq, ret);
630                 free_irq(bc->rx_irq, bc);
631                 return ret;
632         }
633 
634         /* The TX IRQ is enabled only when we can't write all the data to the
635          * byte channel at once, so by default it's disabled.
636          */
637         disable_tx_interrupt(bc);
638 
639         return 0;
640 }
641 
642 static void ehv_bc_tty_port_shutdown(struct tty_port *port)
643 {
644         struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
645 
646         free_irq(bc->tx_irq, bc);
647         free_irq(bc->rx_irq, bc);
648 }
649 
650 static const struct tty_port_operations ehv_bc_tty_port_ops = {
651         .activate = ehv_bc_tty_port_activate,
652         .shutdown = ehv_bc_tty_port_shutdown,
653 };
654 
655 static int ehv_bc_tty_probe(struct platform_device *pdev)
656 {
657         struct device_node *np = pdev->dev.of_node;
658         struct ehv_bc_data *bc;
659         const uint32_t *iprop;
660         unsigned int handle;
661         int ret;
662         static unsigned int index = 1;
663         unsigned int i;
664 
665         iprop = of_get_property(np, "hv-handle", NULL);
666         if (!iprop) {
667                 dev_err(&pdev->dev, "no 'hv-handle' property in %s node\n",
668                         np->name);
669                 return -ENODEV;
670         }
671 
672         /* We already told the console layer that the index for the console
673          * device is zero, so we need to make sure that we use that index when
674          * we probe the console byte channel node.
675          */
676         handle = be32_to_cpu(*iprop);
677         i = (handle == stdout_bc) ? 0 : index++;
678         bc = &bcs[i];
679 
680         bc->handle = handle;
681         bc->head = 0;
682         bc->tail = 0;
683         spin_lock_init(&bc->lock);
684 
685         bc->rx_irq = irq_of_parse_and_map(np, 0);
686         bc->tx_irq = irq_of_parse_and_map(np, 1);
687         if ((bc->rx_irq == NO_IRQ) || (bc->tx_irq == NO_IRQ)) {
688                 dev_err(&pdev->dev, "no 'interrupts' property in %s node\n",
689                         np->name);
690                 ret = -ENODEV;
691                 goto error;
692         }
693 
694         tty_port_init(&bc->port);
695         bc->port.ops = &ehv_bc_tty_port_ops;
696 
697         bc->dev = tty_port_register_device(&bc->port, ehv_bc_driver, i,
698                         &pdev->dev);
699         if (IS_ERR(bc->dev)) {
700                 ret = PTR_ERR(bc->dev);
701                 dev_err(&pdev->dev, "could not register tty (ret=%i)\n", ret);
702                 goto error;
703         }
704 
705         dev_set_drvdata(&pdev->dev, bc);
706 
707         dev_info(&pdev->dev, "registered /dev/%s%u for byte channel %u\n",
708                 ehv_bc_driver->name, i, bc->handle);
709 
710         return 0;
711 
712 error:
713         tty_port_destroy(&bc->port);
714         irq_dispose_mapping(bc->tx_irq);
715         irq_dispose_mapping(bc->rx_irq);
716 
717         memset(bc, 0, sizeof(struct ehv_bc_data));
718         return ret;
719 }
720 
721 static const struct of_device_id ehv_bc_tty_of_ids[] = {
722         { .compatible = "epapr,hv-byte-channel" },
723         {}
724 };
725 
726 static struct platform_driver ehv_bc_tty_driver = {
727         .driver = {
728                 .name = "ehv-bc",
729                 .of_match_table = ehv_bc_tty_of_ids,
730                 .suppress_bind_attrs = true,
731         },
732         .probe          = ehv_bc_tty_probe,
733 };
734 
735 /**
736  * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
737  *
738  * This function is called when this driver is loaded.
739  */
740 static int __init ehv_bc_init(void)
741 {
742         struct device_node *np;
743         unsigned int count = 0; /* Number of elements in bcs[] */
744         int ret;
745 
746         pr_info("ePAPR hypervisor byte channel driver\n");
747 
748         /* Count the number of byte channels */
749         for_each_compatible_node(np, NULL, "epapr,hv-byte-channel")
750                 count++;
751 
752         if (!count)
753                 return -ENODEV;
754 
755         /* The array index of an element in bcs[] is the same as the tty index
756          * for that element.  If you know the address of an element in the
757          * array, then you can use pointer math (e.g. "bc - bcs") to get its
758          * tty index.
759          */
760         bcs = kzalloc(count * sizeof(struct ehv_bc_data), GFP_KERNEL);
761         if (!bcs)
762                 return -ENOMEM;
763 
764         ehv_bc_driver = alloc_tty_driver(count);
765         if (!ehv_bc_driver) {
766                 ret = -ENOMEM;
767                 goto error;
768         }
769 
770         ehv_bc_driver->driver_name = "ehv-bc";
771         ehv_bc_driver->name = ehv_bc_console.name;
772         ehv_bc_driver->type = TTY_DRIVER_TYPE_CONSOLE;
773         ehv_bc_driver->subtype = SYSTEM_TYPE_CONSOLE;
774         ehv_bc_driver->init_termios = tty_std_termios;
775         ehv_bc_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
776         tty_set_operations(ehv_bc_driver, &ehv_bc_ops);
777 
778         ret = tty_register_driver(ehv_bc_driver);
779         if (ret) {
780                 pr_err("ehv-bc: could not register tty driver (ret=%i)\n", ret);
781                 goto error;
782         }
783 
784         ret = platform_driver_register(&ehv_bc_tty_driver);
785         if (ret) {
786                 pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
787                        ret);
788                 goto error;
789         }
790 
791         return 0;
792 
793 error:
794         if (ehv_bc_driver) {
795                 tty_unregister_driver(ehv_bc_driver);
796                 put_tty_driver(ehv_bc_driver);
797         }
798 
799         kfree(bcs);
800 
801         return ret;
802 }
803 device_initcall(ehv_bc_init);
804 

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