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