1 // SPDX-License-Identifier: GPL-2.0
2 /* ePAPR hypervisor byte channel device driver
4 * Copyright 2009-2011 Freescale Semiconductor, Inc.
6 * Author: Timur Tabi <timur@freescale.com>
8 * This driver support three distinct interfaces, all of which are related to
9 * ePAPR hypervisor byte channels.
11 * 1) An early-console (udbg) driver. This provides early console output
12 * through a byte channel. The byte channel handle must be specified in a
15 * 2) A normal console driver. Output is sent to the byte channel designated
16 * for stdout in the device tree. The console driver is for handling kernel
19 * 3) A tty driver, which is used to handle user-space input and output. The
20 * byte channel used for the console is designated as the default tty.
23 #include <linux/init.h>
24 #include <linux/slab.h>
25 #include <linux/err.h>
26 #include <linux/interrupt.h>
28 #include <linux/poll.h>
29 #include <asm/epapr_hcalls.h>
31 #include <linux/of_irq.h>
32 #include <linux/platform_device.h>
33 #include <linux/cdev.h>
34 #include <linux/console.h>
35 #include <linux/tty.h>
36 #include <linux/tty_flip.h>
37 #include <linux/circ_buf.h>
40 /* The size of the transmit circular buffer. This must be a power of two. */
43 /* Per-byte channel private data */
51 spinlock_t lock
; /* lock for transmit buffer */
52 unsigned char buf
[BUF_SIZE
]; /* transmit circular buffer */
53 unsigned int head
; /* circular buffer head */
54 unsigned int tail
; /* circular buffer tail */
56 int tx_irq_enabled
; /* true == TX interrupt is enabled */
59 /* Array of byte channel objects */
60 static struct ehv_bc_data
*bcs
;
62 /* Byte channel handle for stdout (and stdin), taken from device tree */
63 static unsigned int stdout_bc
;
65 /* Virtual IRQ for the byte channel handle for stdin, taken from device tree */
66 static unsigned int stdout_irq
;
68 /**************************** SUPPORT FUNCTIONS ****************************/
71 * Enable the transmit interrupt
73 * Unlike a serial device, byte channels have no mechanism for disabling their
74 * own receive or transmit interrupts. To emulate that feature, we toggle
75 * the IRQ in the kernel.
77 * We cannot just blindly call enable_irq() or disable_irq(), because these
78 * calls are reference counted. This means that we cannot call enable_irq()
79 * if interrupts are already enabled. This can happen in two situations:
81 * 1. The tty layer makes two back-to-back calls to ehv_bc_tty_write()
82 * 2. A transmit interrupt occurs while executing ehv_bc_tx_dequeue()
84 * To work around this, we keep a flag to tell us if the IRQ is enabled or not.
86 static void enable_tx_interrupt(struct ehv_bc_data
*bc
)
88 if (!bc
->tx_irq_enabled
) {
89 enable_irq(bc
->tx_irq
);
90 bc
->tx_irq_enabled
= 1;
94 static void disable_tx_interrupt(struct ehv_bc_data
*bc
)
96 if (bc
->tx_irq_enabled
) {
97 disable_irq_nosync(bc
->tx_irq
);
98 bc
->tx_irq_enabled
= 0;
103 * find the byte channel handle to use for the console
105 * The byte channel to be used for the console is specified via a "stdout"
106 * property in the /chosen node.
108 static int find_console_handle(void)
110 struct device_node
*np
= of_stdout
;
111 const uint32_t *iprop
;
113 /* We don't care what the aliased node is actually called. We only
114 * care if it's compatible with "epapr,hv-byte-channel", because that
115 * indicates that it's a byte channel node.
117 if (!np
|| !of_device_is_compatible(np
, "epapr,hv-byte-channel"))
120 stdout_irq
= irq_of_parse_and_map(np
, 0);
121 if (stdout_irq
== NO_IRQ
) {
122 pr_err("ehv-bc: no 'interrupts' property in %pOF node\n", np
);
127 * The 'hv-handle' property contains the handle for this byte channel.
129 iprop
= of_get_property(np
, "hv-handle", NULL
);
131 pr_err("ehv-bc: no 'hv-handle' property in %s node\n",
135 stdout_bc
= be32_to_cpu(*iprop
);
139 /*************************** EARLY CONSOLE DRIVER ***************************/
141 #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
144 * send a byte to a byte channel, wait if necessary
146 * This function sends a byte to a byte channel, and it waits and
147 * retries if the byte channel is full. It returns if the character
148 * has been sent, or if some error has occurred.
151 static void byte_channel_spin_send(const char data
)
157 ret
= ev_byte_channel_send(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE
,
159 } while (ret
== EV_EAGAIN
);
163 * The udbg subsystem calls this function to display a single character.
164 * We convert CR to a CR/LF.
166 static void ehv_bc_udbg_putc(char c
)
169 byte_channel_spin_send('\r');
171 byte_channel_spin_send(c
);
175 * early console initialization
177 * PowerPC kernels support an early printk console, also known as udbg.
178 * This function must be called via the ppc_md.init_early function pointer.
179 * At this point, the device tree has been unflattened, so we can obtain the
180 * byte channel handle for stdout.
182 * We only support displaying of characters (putc). We do not support
185 void __init
udbg_init_ehv_bc(void)
187 unsigned int rx_count
, tx_count
;
190 /* Verify the byte channel handle */
191 ret
= ev_byte_channel_poll(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE
,
192 &rx_count
, &tx_count
);
196 udbg_putc
= ehv_bc_udbg_putc
;
197 register_early_udbg_console();
199 udbg_printf("ehv-bc: early console using byte channel handle %u\n",
200 CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE
);
205 /****************************** CONSOLE DRIVER ******************************/
207 static struct tty_driver
*ehv_bc_driver
;
210 * Byte channel console sending worker function.
212 * For consoles, if the output buffer is full, we should just spin until it
215 static int ehv_bc_console_byte_channel_send(unsigned int handle
, const char *s
,
222 len
= min_t(unsigned int, count
, EV_BYTE_CHANNEL_MAX_BYTES
);
224 ret
= ev_byte_channel_send(handle
, &len
, s
);
225 } while (ret
== EV_EAGAIN
);
234 * write a string to the console
236 * This function gets called to write a string from the kernel, typically from
237 * a printk(). This function spins until all data is written.
239 * We copy the data to a temporary buffer because we need to insert a \r in
240 * front of every \n. It's more efficient to copy the data to the buffer than
241 * it is to make multiple hcalls for each character or each newline.
243 static void ehv_bc_console_write(struct console
*co
, const char *s
,
246 char s2
[EV_BYTE_CHANNEL_MAX_BYTES
];
247 unsigned int i
, j
= 0;
250 for (i
= 0; i
< count
; i
++) {
257 if (j
>= (EV_BYTE_CHANNEL_MAX_BYTES
- 1)) {
258 if (ehv_bc_console_byte_channel_send(stdout_bc
, s2
, j
))
265 ehv_bc_console_byte_channel_send(stdout_bc
, s2
, j
);
269 * When /dev/console is opened, the kernel iterates the console list looking
270 * for one with ->device and then calls that method. On success, it expects
271 * the passed-in int* to contain the minor number to use.
273 static struct tty_driver
*ehv_bc_console_device(struct console
*co
, int *index
)
277 return ehv_bc_driver
;
280 static struct console ehv_bc_console
= {
282 .write
= ehv_bc_console_write
,
283 .device
= ehv_bc_console_device
,
284 .flags
= CON_PRINTBUFFER
| CON_ENABLED
,
288 * Console initialization
290 * This is the first function that is called after the device tree is
291 * available, so here is where we determine the byte channel handle and IRQ for
292 * stdout/stdin, even though that information is used by the tty and character
295 static int __init
ehv_bc_console_init(void)
297 if (!find_console_handle()) {
298 pr_debug("ehv-bc: stdout is not a byte channel\n");
302 #ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
303 /* Print a friendly warning if the user chose the wrong byte channel
306 if (stdout_bc
!= CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE
)
307 pr_warn("ehv-bc: udbg handle %u is not the stdout handle\n",
308 CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE
);
311 /* add_preferred_console() must be called before register_console(),
312 otherwise it won't work. However, we don't want to enumerate all the
313 byte channels here, either, since we only care about one. */
315 add_preferred_console(ehv_bc_console
.name
, ehv_bc_console
.index
, NULL
);
316 register_console(&ehv_bc_console
);
318 pr_info("ehv-bc: registered console driver for byte channel %u\n",
323 console_initcall(ehv_bc_console_init
);
325 /******************************** TTY DRIVER ********************************/
328 * byte channel receive interrupt handler
330 * This ISR is called whenever data is available on a byte channel.
332 static irqreturn_t
ehv_bc_tty_rx_isr(int irq
, void *data
)
334 struct ehv_bc_data
*bc
= data
;
335 unsigned int rx_count
, tx_count
, len
;
337 char buffer
[EV_BYTE_CHANNEL_MAX_BYTES
];
340 /* Find out how much data needs to be read, and then ask the TTY layer
341 * if it can handle that much. We want to ensure that every byte we
342 * read from the byte channel will be accepted by the TTY layer.
344 ev_byte_channel_poll(bc
->handle
, &rx_count
, &tx_count
);
345 count
= tty_buffer_request_room(&bc
->port
, rx_count
);
347 /* 'count' is the maximum amount of data the TTY layer can accept at
348 * this time. However, during testing, I was never able to get 'count'
349 * to be less than 'rx_count'. I'm not sure whether I'm calling it
354 len
= min_t(unsigned int, count
, sizeof(buffer
));
356 /* Read some data from the byte channel. This function will
357 * never return more than EV_BYTE_CHANNEL_MAX_BYTES bytes.
359 ev_byte_channel_receive(bc
->handle
, &len
, buffer
);
361 /* 'len' is now the amount of data that's been received. 'len'
362 * can't be zero, and most likely it's equal to one.
365 /* Pass the received data to the tty layer. */
366 ret
= tty_insert_flip_string(&bc
->port
, buffer
, len
);
368 /* 'ret' is the number of bytes that the TTY layer accepted.
369 * If it's not equal to 'len', then it means the buffer is
370 * full, which should never happen. If it does happen, we can
371 * exit gracefully, but we drop the last 'len - ret' characters
372 * that we read from the byte channel.
380 /* Tell the tty layer that we're done. */
381 tty_flip_buffer_push(&bc
->port
);
387 * dequeue the transmit buffer to the hypervisor
389 * This function, which can be called in interrupt context, dequeues as much
390 * data as possible from the transmit buffer to the byte channel.
392 static void ehv_bc_tx_dequeue(struct ehv_bc_data
*bc
)
395 unsigned int len
, ret
;
399 spin_lock_irqsave(&bc
->lock
, flags
);
400 len
= min_t(unsigned int,
401 CIRC_CNT_TO_END(bc
->head
, bc
->tail
, BUF_SIZE
),
402 EV_BYTE_CHANNEL_MAX_BYTES
);
404 ret
= ev_byte_channel_send(bc
->handle
, &len
, bc
->buf
+ bc
->tail
);
406 /* 'len' is valid only if the return code is 0 or EV_EAGAIN */
407 if (!ret
|| (ret
== EV_EAGAIN
))
408 bc
->tail
= (bc
->tail
+ len
) & (BUF_SIZE
- 1);
410 count
= CIRC_CNT(bc
->head
, bc
->tail
, BUF_SIZE
);
411 spin_unlock_irqrestore(&bc
->lock
, flags
);
412 } while (count
&& !ret
);
414 spin_lock_irqsave(&bc
->lock
, flags
);
415 if (CIRC_CNT(bc
->head
, bc
->tail
, BUF_SIZE
))
417 * If we haven't emptied the buffer, then enable the TX IRQ.
418 * We'll get an interrupt when there's more room in the
419 * hypervisor's output buffer.
421 enable_tx_interrupt(bc
);
423 disable_tx_interrupt(bc
);
424 spin_unlock_irqrestore(&bc
->lock
, flags
);
428 * byte channel transmit interrupt handler
430 * This ISR is called whenever space becomes available for transmitting
431 * characters on a byte channel.
433 static irqreturn_t
ehv_bc_tty_tx_isr(int irq
, void *data
)
435 struct ehv_bc_data
*bc
= data
;
437 ehv_bc_tx_dequeue(bc
);
438 tty_port_tty_wakeup(&bc
->port
);
444 * This function is called when the tty layer has data for us send. We store
445 * the data first in a circular buffer, and then dequeue as much of that data
448 * We don't need to worry about whether there is enough room in the buffer for
449 * all the data. The purpose of ehv_bc_tty_write_room() is to tell the tty
450 * layer how much data it can safely send to us. We guarantee that
451 * ehv_bc_tty_write_room() will never lie, so the tty layer will never send us
454 static int ehv_bc_tty_write(struct tty_struct
*ttys
, const unsigned char *s
,
457 struct ehv_bc_data
*bc
= ttys
->driver_data
;
460 unsigned int written
= 0;
463 spin_lock_irqsave(&bc
->lock
, flags
);
464 len
= CIRC_SPACE_TO_END(bc
->head
, bc
->tail
, BUF_SIZE
);
468 memcpy(bc
->buf
+ bc
->head
, s
, len
);
469 bc
->head
= (bc
->head
+ len
) & (BUF_SIZE
- 1);
471 spin_unlock_irqrestore(&bc
->lock
, flags
);
480 ehv_bc_tx_dequeue(bc
);
486 * This function can be called multiple times for a given tty_struct, which is
487 * why we initialize bc->ttys in ehv_bc_tty_port_activate() instead.
489 * The tty layer will still call this function even if the device was not
490 * registered (i.e. tty_register_device() was not called). This happens
491 * because tty_register_device() is optional and some legacy drivers don't
492 * use it. So we need to check for that.
494 static int ehv_bc_tty_open(struct tty_struct
*ttys
, struct file
*filp
)
496 struct ehv_bc_data
*bc
= &bcs
[ttys
->index
];
501 return tty_port_open(&bc
->port
, ttys
, filp
);
505 * Amazingly, if ehv_bc_tty_open() returns an error code, the tty layer will
506 * still call this function to close the tty device. So we can't assume that
507 * the tty port has been initialized.
509 static void ehv_bc_tty_close(struct tty_struct
*ttys
, struct file
*filp
)
511 struct ehv_bc_data
*bc
= &bcs
[ttys
->index
];
514 tty_port_close(&bc
->port
, ttys
, filp
);
518 * Return the amount of space in the output buffer
520 * This is actually a contract between the driver and the tty layer outlining
521 * how much write room the driver can guarantee will be sent OR BUFFERED. This
522 * driver MUST honor the return value.
524 static int ehv_bc_tty_write_room(struct tty_struct
*ttys
)
526 struct ehv_bc_data
*bc
= ttys
->driver_data
;
530 spin_lock_irqsave(&bc
->lock
, flags
);
531 count
= CIRC_SPACE(bc
->head
, bc
->tail
, BUF_SIZE
);
532 spin_unlock_irqrestore(&bc
->lock
, flags
);
538 * Stop sending data to the tty layer
540 * This function is called when the tty layer's input buffers are getting full,
541 * so the driver should stop sending it data. The easiest way to do this is to
542 * disable the RX IRQ, which will prevent ehv_bc_tty_rx_isr() from being
545 * The hypervisor will continue to queue up any incoming data. If there is any
546 * data in the queue when the RX interrupt is enabled, we'll immediately get an
549 static void ehv_bc_tty_throttle(struct tty_struct
*ttys
)
551 struct ehv_bc_data
*bc
= ttys
->driver_data
;
553 disable_irq(bc
->rx_irq
);
557 * Resume sending data to the tty layer
559 * This function is called after previously calling ehv_bc_tty_throttle(). The
560 * tty layer's input buffers now have more room, so the driver can resume
563 static void ehv_bc_tty_unthrottle(struct tty_struct
*ttys
)
565 struct ehv_bc_data
*bc
= ttys
->driver_data
;
567 /* If there is any data in the queue when the RX interrupt is enabled,
568 * we'll immediately get an RX interrupt.
570 enable_irq(bc
->rx_irq
);
573 static void ehv_bc_tty_hangup(struct tty_struct
*ttys
)
575 struct ehv_bc_data
*bc
= ttys
->driver_data
;
577 ehv_bc_tx_dequeue(bc
);
578 tty_port_hangup(&bc
->port
);
582 * TTY driver operations
584 * If we could ask the hypervisor how much data is still in the TX buffer, or
585 * at least how big the TX buffers are, then we could implement the
586 * .wait_until_sent and .chars_in_buffer functions.
588 static const struct tty_operations ehv_bc_ops
= {
589 .open
= ehv_bc_tty_open
,
590 .close
= ehv_bc_tty_close
,
591 .write
= ehv_bc_tty_write
,
592 .write_room
= ehv_bc_tty_write_room
,
593 .throttle
= ehv_bc_tty_throttle
,
594 .unthrottle
= ehv_bc_tty_unthrottle
,
595 .hangup
= ehv_bc_tty_hangup
,
599 * initialize the TTY port
601 * This function will only be called once, no matter how many times
602 * ehv_bc_tty_open() is called. That's why we register the ISR here, and also
603 * why we initialize tty_struct-related variables here.
605 static int ehv_bc_tty_port_activate(struct tty_port
*port
,
606 struct tty_struct
*ttys
)
608 struct ehv_bc_data
*bc
= container_of(port
, struct ehv_bc_data
, port
);
611 ttys
->driver_data
= bc
;
613 ret
= request_irq(bc
->rx_irq
, ehv_bc_tty_rx_isr
, 0, "ehv-bc", bc
);
615 dev_err(bc
->dev
, "could not request rx irq %u (ret=%i)\n",
620 /* request_irq also enables the IRQ */
621 bc
->tx_irq_enabled
= 1;
623 ret
= request_irq(bc
->tx_irq
, ehv_bc_tty_tx_isr
, 0, "ehv-bc", bc
);
625 dev_err(bc
->dev
, "could not request tx irq %u (ret=%i)\n",
627 free_irq(bc
->rx_irq
, bc
);
631 /* The TX IRQ is enabled only when we can't write all the data to the
632 * byte channel at once, so by default it's disabled.
634 disable_tx_interrupt(bc
);
639 static void ehv_bc_tty_port_shutdown(struct tty_port
*port
)
641 struct ehv_bc_data
*bc
= container_of(port
, struct ehv_bc_data
, port
);
643 free_irq(bc
->tx_irq
, bc
);
644 free_irq(bc
->rx_irq
, bc
);
647 static const struct tty_port_operations ehv_bc_tty_port_ops
= {
648 .activate
= ehv_bc_tty_port_activate
,
649 .shutdown
= ehv_bc_tty_port_shutdown
,
652 static int ehv_bc_tty_probe(struct platform_device
*pdev
)
654 struct device_node
*np
= pdev
->dev
.of_node
;
655 struct ehv_bc_data
*bc
;
656 const uint32_t *iprop
;
659 static unsigned int index
= 1;
662 iprop
= of_get_property(np
, "hv-handle", NULL
);
664 dev_err(&pdev
->dev
, "no 'hv-handle' property in %s node\n",
669 /* We already told the console layer that the index for the console
670 * device is zero, so we need to make sure that we use that index when
671 * we probe the console byte channel node.
673 handle
= be32_to_cpu(*iprop
);
674 i
= (handle
== stdout_bc
) ? 0 : index
++;
680 spin_lock_init(&bc
->lock
);
682 bc
->rx_irq
= irq_of_parse_and_map(np
, 0);
683 bc
->tx_irq
= irq_of_parse_and_map(np
, 1);
684 if ((bc
->rx_irq
== NO_IRQ
) || (bc
->tx_irq
== NO_IRQ
)) {
685 dev_err(&pdev
->dev
, "no 'interrupts' property in %s node\n",
691 tty_port_init(&bc
->port
);
692 bc
->port
.ops
= &ehv_bc_tty_port_ops
;
694 bc
->dev
= tty_port_register_device(&bc
->port
, ehv_bc_driver
, i
,
696 if (IS_ERR(bc
->dev
)) {
697 ret
= PTR_ERR(bc
->dev
);
698 dev_err(&pdev
->dev
, "could not register tty (ret=%i)\n", ret
);
702 dev_set_drvdata(&pdev
->dev
, bc
);
704 dev_info(&pdev
->dev
, "registered /dev/%s%u for byte channel %u\n",
705 ehv_bc_driver
->name
, i
, bc
->handle
);
710 tty_port_destroy(&bc
->port
);
711 irq_dispose_mapping(bc
->tx_irq
);
712 irq_dispose_mapping(bc
->rx_irq
);
714 memset(bc
, 0, sizeof(struct ehv_bc_data
));
718 static const struct of_device_id ehv_bc_tty_of_ids
[] = {
719 { .compatible
= "epapr,hv-byte-channel" },
723 static struct platform_driver ehv_bc_tty_driver
= {
726 .of_match_table
= ehv_bc_tty_of_ids
,
727 .suppress_bind_attrs
= true,
729 .probe
= ehv_bc_tty_probe
,
733 * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
735 * This function is called when this driver is loaded.
737 static int __init
ehv_bc_init(void)
739 struct device_node
*np
;
740 unsigned int count
= 0; /* Number of elements in bcs[] */
743 pr_info("ePAPR hypervisor byte channel driver\n");
745 /* Count the number of byte channels */
746 for_each_compatible_node(np
, NULL
, "epapr,hv-byte-channel")
752 /* The array index of an element in bcs[] is the same as the tty index
753 * for that element. If you know the address of an element in the
754 * array, then you can use pointer math (e.g. "bc - bcs") to get its
757 bcs
= kzalloc(count
* sizeof(struct ehv_bc_data
), GFP_KERNEL
);
761 ehv_bc_driver
= alloc_tty_driver(count
);
762 if (!ehv_bc_driver
) {
767 ehv_bc_driver
->driver_name
= "ehv-bc";
768 ehv_bc_driver
->name
= ehv_bc_console
.name
;
769 ehv_bc_driver
->type
= TTY_DRIVER_TYPE_CONSOLE
;
770 ehv_bc_driver
->subtype
= SYSTEM_TYPE_CONSOLE
;
771 ehv_bc_driver
->init_termios
= tty_std_termios
;
772 ehv_bc_driver
->flags
= TTY_DRIVER_REAL_RAW
| TTY_DRIVER_DYNAMIC_DEV
;
773 tty_set_operations(ehv_bc_driver
, &ehv_bc_ops
);
775 ret
= tty_register_driver(ehv_bc_driver
);
777 pr_err("ehv-bc: could not register tty driver (ret=%i)\n", ret
);
778 goto err_put_tty_driver
;
781 ret
= platform_driver_register(&ehv_bc_tty_driver
);
783 pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
785 goto err_deregister_tty_driver
;
790 err_deregister_tty_driver
:
791 tty_unregister_driver(ehv_bc_driver
);
793 put_tty_driver(ehv_bc_driver
);
799 device_initcall(ehv_bc_init
);