1 /* ePAPR hypervisor byte channel device driver
3 * Copyright 2009-2011 Freescale Semiconductor, Inc.
5 * Author: Timur Tabi <timur@freescale.com>
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.
11 * This driver support three distinct interfaces, all of which are related to
12 * ePAPR hypervisor byte channels.
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
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
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.
26 #include <linux/init.h>
27 #include <linux/slab.h>
28 #include <linux/err.h>
29 #include <linux/interrupt.h>
31 #include <linux/poll.h>
32 #include <asm/epapr_hcalls.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>
43 /* The size of the transmit circular buffer. This must be a power of two. */
46 /* Per-byte channel private data */
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 */
59 int tx_irq_enabled; /* true == TX interrupt is enabled */
62 /* Array of byte channel objects */
63 static struct ehv_bc_data *bcs;
65 /* Byte channel handle for stdout (and stdin), taken from device tree */
66 static unsigned int stdout_bc;
68 /* Virtual IRQ for the byte channel handle for stdin, taken from device tree */
69 static unsigned int stdout_irq;
71 /**************************** SUPPORT FUNCTIONS ****************************/
74 * Enable the transmit interrupt
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.
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:
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()
87 * To work around this, we keep a flag to tell us if the IRQ is enabled or not.
89 static void enable_tx_interrupt(struct ehv_bc_data *bc)
91 if (!bc->tx_irq_enabled) {
92 enable_irq(bc->tx_irq);
93 bc->tx_irq_enabled = 1;
97 static void disable_tx_interrupt(struct ehv_bc_data *bc)
99 if (bc->tx_irq_enabled) {
100 disable_irq_nosync(bc->tx_irq);
101 bc->tx_irq_enabled = 0;
106 * find the byte channel handle to use for the console
108 * The byte channel to be used for the console is specified via a "stdout"
109 * property in the /chosen node.
111 static int find_console_handle(void)
113 struct device_node *np = of_stdout;
114 const uint32_t *iprop;
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.
120 if (!np || !of_device_is_compatible(np, "epapr,hv-byte-channel"))
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 %pOF node\n", np);
130 * The 'hv-handle' property contains the handle for this byte channel.
132 iprop = of_get_property(np, "hv-handle", NULL);
134 pr_err("ehv-bc: no 'hv-handle' property in %s node\n",
138 stdout_bc = be32_to_cpu(*iprop);
142 /*************************** EARLY CONSOLE DRIVER ***************************/
144 #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
147 * send a byte to a byte channel, wait if necessary
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.
154 static void byte_channel_spin_send(const char data)
160 ret = ev_byte_channel_send(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
162 } while (ret == EV_EAGAIN);
166 * The udbg subsystem calls this function to display a single character.
167 * We convert CR to a CR/LF.
169 static void ehv_bc_udbg_putc(char c)
172 byte_channel_spin_send('\r');
174 byte_channel_spin_send(c);
178 * early console initialization
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.
185 * We only support displaying of characters (putc). We do not support
188 void __init udbg_init_ehv_bc(void)
190 unsigned int rx_count, tx_count;
193 /* Verify the byte channel handle */
194 ret = ev_byte_channel_poll(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
195 &rx_count, &tx_count);
199 udbg_putc = ehv_bc_udbg_putc;
200 register_early_udbg_console();
202 udbg_printf("ehv-bc: early console using byte channel handle %u\n",
203 CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
208 /****************************** CONSOLE DRIVER ******************************/
210 static struct tty_driver *ehv_bc_driver;
213 * Byte channel console sending worker function.
215 * For consoles, if the output buffer is full, we should just spin until it
218 static int ehv_bc_console_byte_channel_send(unsigned int handle, const char *s,
225 len = min_t(unsigned int, count, EV_BYTE_CHANNEL_MAX_BYTES);
227 ret = ev_byte_channel_send(handle, &len, s);
228 } while (ret == EV_EAGAIN);
237 * write a string to the console
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.
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.
246 static void ehv_bc_console_write(struct console *co, const char *s,
249 char s2[EV_BYTE_CHANNEL_MAX_BYTES];
250 unsigned int i, j = 0;
253 for (i = 0; i < count; i++) {
260 if (j >= (EV_BYTE_CHANNEL_MAX_BYTES - 1)) {
261 if (ehv_bc_console_byte_channel_send(stdout_bc, s2, j))
268 ehv_bc_console_byte_channel_send(stdout_bc, s2, j);
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.
276 static struct tty_driver *ehv_bc_console_device(struct console *co, int *index)
280 return ehv_bc_driver;
283 static struct console ehv_bc_console = {
285 .write = ehv_bc_console_write,
286 .device = ehv_bc_console_device,
287 .flags = CON_PRINTBUFFER | CON_ENABLED,
291 * Console initialization
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
298 static int __init ehv_bc_console_init(void)
300 if (!find_console_handle()) {
301 pr_debug("ehv-bc: stdout is not a byte channel\n");
305 #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
306 /* Print a friendly warning if the user chose the wrong byte channel
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);
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. */
318 add_preferred_console(ehv_bc_console.name, ehv_bc_console.index, NULL);
319 register_console(&ehv_bc_console);
321 pr_info("ehv-bc: registered console driver for byte channel %u\n",
326 console_initcall(ehv_bc_console_init);
328 /******************************** TTY DRIVER ********************************/
331 * byte channel receive interupt handler
333 * This ISR is called whenever data is available on a byte channel.
335 static irqreturn_t ehv_bc_tty_rx_isr(int irq, void *data)
337 struct ehv_bc_data *bc = data;
338 unsigned int rx_count, tx_count, len;
340 char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
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.
347 ev_byte_channel_poll(bc->handle, &rx_count, &tx_count);
348 count = tty_buffer_request_room(&bc->port, rx_count);
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
357 len = min_t(unsigned int, count, sizeof(buffer));
359 /* Read some data from the byte channel. This function will
360 * never return more than EV_BYTE_CHANNEL_MAX_BYTES bytes.
362 ev_byte_channel_receive(bc->handle, &len, buffer);
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.
368 /* Pass the received data to the tty layer. */
369 ret = tty_insert_flip_string(&bc->port, buffer, len);
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.
383 /* Tell the tty layer that we're done. */
384 tty_flip_buffer_push(&bc->port);
390 * dequeue the transmit buffer to the hypervisor
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.
395 static void ehv_bc_tx_dequeue(struct ehv_bc_data *bc)
398 unsigned int len, ret;
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);
407 ret = ev_byte_channel_send(bc->handle, &len, bc->buf + bc->tail);
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);
413 count = CIRC_CNT(bc->head, bc->tail, BUF_SIZE);
414 spin_unlock_irqrestore(&bc->lock, flags);
415 } while (count && !ret);
417 spin_lock_irqsave(&bc->lock, flags);
418 if (CIRC_CNT(bc->head, bc->tail, BUF_SIZE))
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.
424 enable_tx_interrupt(bc);
426 disable_tx_interrupt(bc);
427 spin_unlock_irqrestore(&bc->lock, flags);
431 * byte channel transmit interupt handler
433 * This ISR is called whenever space becomes available for transmitting
434 * characters on a byte channel.
436 static irqreturn_t ehv_bc_tty_tx_isr(int irq, void *data)
438 struct ehv_bc_data *bc = data;
440 ehv_bc_tx_dequeue(bc);
441 tty_port_tty_wakeup(&bc->port);
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
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
457 static int ehv_bc_tty_write(struct tty_struct *ttys, const unsigned char *s,
460 struct ehv_bc_data *bc = ttys->driver_data;
463 unsigned int written = 0;
466 spin_lock_irqsave(&bc->lock, flags);
467 len = CIRC_SPACE_TO_END(bc->head, bc->tail, BUF_SIZE);
471 memcpy(bc->buf + bc->head, s, len);
472 bc->head = (bc->head + len) & (BUF_SIZE - 1);
474 spin_unlock_irqrestore(&bc->lock, flags);
483 ehv_bc_tx_dequeue(bc);
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.
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.
497 static int ehv_bc_tty_open(struct tty_struct *ttys, struct file *filp)
499 struct ehv_bc_data *bc = &bcs[ttys->index];
504 return tty_port_open(&bc->port, ttys, filp);
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.
512 static void ehv_bc_tty_close(struct tty_struct *ttys, struct file *filp)
514 struct ehv_bc_data *bc = &bcs[ttys->index];
517 tty_port_close(&bc->port, ttys, filp);
521 * Return the amount of space in the output buffer
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.
527 static int ehv_bc_tty_write_room(struct tty_struct *ttys)
529 struct ehv_bc_data *bc = ttys->driver_data;
533 spin_lock_irqsave(&bc->lock, flags);
534 count = CIRC_SPACE(bc->head, bc->tail, BUF_SIZE);
535 spin_unlock_irqrestore(&bc->lock, flags);
541 * Stop sending data to the tty layer
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
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
552 static void ehv_bc_tty_throttle(struct tty_struct *ttys)
554 struct ehv_bc_data *bc = ttys->driver_data;
556 disable_irq(bc->rx_irq);
560 * Resume sending data to the tty layer
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
566 static void ehv_bc_tty_unthrottle(struct tty_struct *ttys)
568 struct ehv_bc_data *bc = ttys->driver_data;
570 /* If there is any data in the queue when the RX interrupt is enabled,
571 * we'll immediately get an RX interrupt.
573 enable_irq(bc->rx_irq);
576 static void ehv_bc_tty_hangup(struct tty_struct *ttys)
578 struct ehv_bc_data *bc = ttys->driver_data;
580 ehv_bc_tx_dequeue(bc);
581 tty_port_hangup(&bc->port);
585 * TTY driver operations
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.
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,
602 * initialize the TTY port
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.
608 static int ehv_bc_tty_port_activate(struct tty_port *port,
609 struct tty_struct *ttys)
611 struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
614 ttys->driver_data = bc;
616 ret = request_irq(bc->rx_irq, ehv_bc_tty_rx_isr, 0, "ehv-bc", bc);
618 dev_err(bc->dev, "could not request rx irq %u (ret=%i)\n",
623 /* request_irq also enables the IRQ */
624 bc->tx_irq_enabled = 1;
626 ret = request_irq(bc->tx_irq, ehv_bc_tty_tx_isr, 0, "ehv-bc", bc);
628 dev_err(bc->dev, "could not request tx irq %u (ret=%i)\n",
630 free_irq(bc->rx_irq, bc);
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.
637 disable_tx_interrupt(bc);
642 static void ehv_bc_tty_port_shutdown(struct tty_port *port)
644 struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
646 free_irq(bc->tx_irq, bc);
647 free_irq(bc->rx_irq, bc);
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,
655 static int ehv_bc_tty_probe(struct platform_device *pdev)
657 struct device_node *np = pdev->dev.of_node;
658 struct ehv_bc_data *bc;
659 const uint32_t *iprop;
662 static unsigned int index = 1;
665 iprop = of_get_property(np, "hv-handle", NULL);
667 dev_err(&pdev->dev, "no 'hv-handle' property in %s node\n",
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.
676 handle = be32_to_cpu(*iprop);
677 i = (handle == stdout_bc) ? 0 : index++;
683 spin_lock_init(&bc->lock);
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",
694 tty_port_init(&bc->port);
695 bc->port.ops = &ehv_bc_tty_port_ops;
697 bc->dev = tty_port_register_device(&bc->port, ehv_bc_driver, i,
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);
705 dev_set_drvdata(&pdev->dev, bc);
707 dev_info(&pdev->dev, "registered /dev/%s%u for byte channel %u\n",
708 ehv_bc_driver->name, i, bc->handle);
713 tty_port_destroy(&bc->port);
714 irq_dispose_mapping(bc->tx_irq);
715 irq_dispose_mapping(bc->rx_irq);
717 memset(bc, 0, sizeof(struct ehv_bc_data));
721 static const struct of_device_id ehv_bc_tty_of_ids[] = {
722 { .compatible = "epapr,hv-byte-channel" },
726 static struct platform_driver ehv_bc_tty_driver = {
729 .of_match_table = ehv_bc_tty_of_ids,
730 .suppress_bind_attrs = true,
732 .probe = ehv_bc_tty_probe,
736 * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
738 * This function is called when this driver is loaded.
740 static int __init ehv_bc_init(void)
742 struct device_node *np;
743 unsigned int count = 0; /* Number of elements in bcs[] */
746 pr_info("ePAPR hypervisor byte channel driver\n");
748 /* Count the number of byte channels */
749 for_each_compatible_node(np, NULL, "epapr,hv-byte-channel")
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
760 bcs = kzalloc(count * sizeof(struct ehv_bc_data), GFP_KERNEL);
764 ehv_bc_driver = alloc_tty_driver(count);
765 if (!ehv_bc_driver) {
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);
778 ret = tty_register_driver(ehv_bc_driver);
780 pr_err("ehv-bc: could not register tty driver (ret=%i)\n", ret);
781 goto err_put_tty_driver;
784 ret = platform_driver_register(&ehv_bc_tty_driver);
786 pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
788 goto err_deregister_tty_driver;
793 err_deregister_tty_driver:
794 tty_unregister_driver(ehv_bc_driver);
796 put_tty_driver(ehv_bc_driver);
802 device_initcall(ehv_bc_init);