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    Subject[PATCH 6/7] tty/powerpc: introduce the ePAPR embedded hypervisor byte channel driver
    Date
    The ePAPR embedded hypervisor specification provides an API for "byte
    channels", which are serial-like virtual devices for sending and receiving
    streams of bytes. This driver provides Linux kernel support for byte
    channels via three distinct interfaces:

    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.

    Signed-off-by: Timur Tabi <timur@freescale.com>
    ---
    arch/powerpc/include/asm/udbg.h | 1 +
    arch/powerpc/kernel/udbg.c | 2 +
    drivers/tty/Kconfig | 33 ++
    drivers/tty/Makefile | 1 +
    drivers/tty/ehv_bytechan.c | 872 +++++++++++++++++++++++++++++++++++++++
    5 files changed, 909 insertions(+), 0 deletions(-)
    create mode 100644 drivers/tty/ehv_bytechan.c

    diff --git a/arch/powerpc/include/asm/udbg.h b/arch/powerpc/include/asm/udbg.h
    index 11ae699..bb9f6b1 100644
    --- a/arch/powerpc/include/asm/udbg.h
    +++ b/arch/powerpc/include/asm/udbg.h
    @@ -52,6 +52,7 @@ extern void __init udbg_init_44x_as1(void);
    extern void __init udbg_init_40x_realmode(void);
    extern void __init udbg_init_cpm(void);
    extern void __init udbg_init_usbgecko(void);
    +extern void __init udbg_init_ehv_bc(void);

    #endif /* __KERNEL__ */
    #endif /* _ASM_POWERPC_UDBG_H */
    diff --git a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
    index e39cad8..d117368 100644
    --- a/arch/powerpc/kernel/udbg.c
    +++ b/arch/powerpc/kernel/udbg.c
    @@ -62,6 +62,8 @@ void __init udbg_early_init(void)
    udbg_init_cpm();
    #elif defined(CONFIG_PPC_EARLY_DEBUG_USBGECKO)
    udbg_init_usbgecko();
    +#elif defined(CONFIG_PPC_EARLY_DEBUG_EHV_BC)
    + udbg_init_ehv_bc();
    #endif

    #ifdef CONFIG_PPC_EARLY_DEBUG
    diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
    index 3fd7199..9fe0212 100644
    --- a/drivers/tty/Kconfig
    +++ b/drivers/tty/Kconfig
    @@ -319,3 +319,36 @@ config N_GSM
    This line discipline provides support for the GSM MUX protocol and
    presents the mux as a set of 61 individual tty devices.

    +config PPC_EPAPR_HV_BYTECHAN
    + tristate "ePAPR hypervisor byte channel driver"
    + depends on PPC
    + help
    + This driver creates /dev entries for each ePAPR hypervisor byte
    + channel, thereby allowing applications to communicate with byte
    + channels as if they were serial ports.
    +
    +config PPC_EARLY_DEBUG_EHV_BC
    + bool "Early console (udbg) support for ePAPR hypervisors"
    + depends on PPC_EPAPR_HV_BYTECHAN
    + help
    + Select this option to enable early console (a.k.a. "udbg") support
    + via an ePAPR byte channel. You also need to choose the byte channel
    + handle below.
    +
    +config PPC_EARLY_DEBUG_EHV_BC_HANDLE
    + int "Byte channel handle for early console (udbg)"
    + depends on PPC_EARLY_DEBUG_EHV_BC
    + default 0
    + help
    + If you want early console (udbg) output through a byte channel,
    + specify the handle of the byte channel to use.
    +
    + For this to work, the byte channel driver must be compiled
    + in-kernel, not as a module.
    +
    + Note that only one early console driver can be enabled, so don't
    + enable any others if you enable this one.
    +
    + If the number you specify is not a valid byte channel handle, then
    + there simply will be no early console output. This is true also
    + if you don't boot under a hypervisor at all.
    diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
    index 690522f..4afebd2 100644
    --- a/drivers/tty/Makefile
    +++ b/drivers/tty/Makefile
    @@ -24,5 +24,6 @@ obj-$(CONFIG_ROCKETPORT) += rocket.o
    obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o
    obj-$(CONFIG_SYNCLINKMP) += synclinkmp.o
    obj-$(CONFIG_SYNCLINK) += synclink.o
    +obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o

    obj-y += ipwireless/
    diff --git a/drivers/tty/ehv_bytechan.c b/drivers/tty/ehv_bytechan.c
    new file mode 100644
    index 0000000..b51fdb2
    --- /dev/null
    +++ b/drivers/tty/ehv_bytechan.c
    @@ -0,0 +1,872 @@
    +/* ePAPR hypervisor byte channel device driver
    + *
    + * Copyright 2009-2011 Freescale Semiconductor, Inc.
    + *
    + * Author: Timur Tabi <timur@freescale.com>
    + *
    + * This file is licensed under the terms of the GNU General Public License
    + * version 2. This program is licensed "as is" without any warranty of any
    + * kind, whether express or implied.
    + *
    + * 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/module.h>
    +#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/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;
    + struct tty_struct *ttys;
    + 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.
    + *
    + * For compatible with legacy device trees, we also look for a "stdout" alias.
    + */
    +static int find_console_handle(void)
    +{
    + struct device_node *np, *np2;
    + const char *sprop = NULL;
    + const uint32_t *iprop;
    +
    + np = of_find_node_by_path("/chosen");
    + if (np)
    + sprop = of_get_property(np, "stdout-path", NULL);
    +
    + if (!np || !sprop) {
    + of_node_put(np);
    + np = of_find_node_by_name(NULL, "aliases");
    + if (np)
    + sprop = of_get_property(np, "stdout", NULL);
    + }
    +
    + if (!sprop) {
    + of_node_put(np);
    + return 0;
    + }
    +
    + /* 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. We use a temporary
    + * variable, 'np2', because we can't release 'np' until we're done with
    + * 'sprop'.
    + */
    + np2 = of_find_node_by_path(sprop);
    + of_node_put(np);
    + np = np2;
    + if (!np) {
    + pr_warning("ehv-bc: stdout node '%s' does not exist\n", sprop);
    + return 0;
    + }
    +
    + /* Is it a byte channel? */
    + if (!of_device_is_compatible(np, "epapr,hv-byte-channel")) {
    + of_node_put(np);
    + return 0;
    + }
    +
    + stdout_irq = irq_of_parse_and_map(np, 0);
    + if (stdout_irq == NO_IRQ) {
    + pr_err("ehv-bc: no 'interrupts' property in %s node\n", sprop);
    + of_node_put(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 %s node\n",
    + np->name);
    + of_node_put(np);
    + return 0;
    + }
    + stdout_bc = be32_to_cpu(*iprop);
    +
    + of_node_put(np);
    + 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;
    +
    + /* Check if we're running as a guest of a hypervisor */
    + if (!(mfmsr() & MSR_GS))
    + return;
    +
    + /* 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)
    +{
    + unsigned int handle = (unsigned int)co->data;
    + 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(handle, s2, j))
    + return;
    + j = 0;
    + }
    + }
    +
    + if (j)
    + ehv_bc_console_byte_channel_send(handle, 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_warning("ehv-bc: udbg handle %u is not the stdout handle\n",
    + CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
    +#endif
    +
    + ehv_bc_console.data = (void *)stdout_bc;
    +
    + /* 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 interupt 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;
    + struct tty_struct *ttys = bc->ttys;
    + 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(ttys, 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. Note that this
    + * function calls tty_buffer_request_room(), so I'm not sure if
    + * we should have also called tty_buffer_request_room().
    + */
    + ret = tty_insert_flip_string(ttys, 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(ttys);
    +
    + 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 interupt 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_wakeup(bc->ttys);
    +
    + 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.
    + *
    + * For some reason, the tty layer will still call this function even if the
    + * device was not registered (i.e. tty_register_device() was not called). 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);
    +}
    +
    +/*
    + * 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,
    +};
    +
    +/*
    + * 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;
    +
    + bc->ttys = ttys;
    + 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);
    + bc->ttys = NULL;
    +}
    +
    +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 __devinit 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 %s node\n",
    + np->name);
    + 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 %s node\n",
    + np->name);
    + ret = -ENODEV;
    + goto error;
    + }
    +
    + bc->dev = tty_register_device(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;
    + }
    +
    + tty_port_init(&bc->port);
    + bc->port.ops = &ehv_bc_tty_port_ops;
    +
    + 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:
    + irq_dispose_mapping(bc->tx_irq);
    + irq_dispose_mapping(bc->rx_irq);
    +
    + memset(bc, 0, sizeof(struct ehv_bc_data));
    + return ret;
    +}
    +
    +static int ehv_bc_tty_remove(struct platform_device *pdev)
    +{
    + struct ehv_bc_data *bc = dev_get_drvdata(&pdev->dev);
    +
    + tty_unregister_device(ehv_bc_driver, bc - bcs);
    +
    + irq_dispose_mapping(bc->tx_irq);
    + irq_dispose_mapping(bc->rx_irq);
    +
    + return 0;
    +}
    +
    +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 = {
    + .owner = THIS_MODULE,
    + .name = "ehv-bc",
    + .of_match_table = ehv_bc_tty_of_ids,
    + },
    + .probe = ehv_bc_tty_probe,
    + .remove = ehv_bc_tty_remove,
    +};
    +
    +/**
    + * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
    + *
    + * This function is called when this module 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 = kzalloc(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 error;
    + }
    +
    + ehv_bc_driver->owner = THIS_MODULE;
    + 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 error;
    + }
    +
    + ret = platform_driver_register(&ehv_bc_tty_driver);
    + if (ret) {
    + pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
    + ret);
    + goto error;
    + }
    +
    + return 0;
    +
    +error:
    + if (ehv_bc_driver) {
    + tty_unregister_driver(ehv_bc_driver);
    + put_tty_driver(ehv_bc_driver);
    + }
    +
    + kfree(bcs);
    +
    + return ret;
    +}
    +
    +
    +/**
    + * ehv_bc_exit - ePAPR hypervisor byte channel driver termination
    + *
    + * This function is called when this driver is unloaded.
    + */
    +static void __exit ehv_bc_exit(void)
    +{
    + tty_unregister_driver(ehv_bc_driver);
    + put_tty_driver(ehv_bc_driver);
    + kfree(bcs);
    +}
    +
    +module_init(ehv_bc_init);
    +module_exit(ehv_bc_exit);
    +
    +MODULE_AUTHOR("Timur Tabi <timur@freescale.com>");
    +MODULE_DESCRIPTION("ePAPR hypervisor byte channel driver");
    +MODULE_LICENSE("GPL v2");
    --
    1.7.3.4



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