// 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);