path: root/drivers/tty/ehv_bytechan.c

// 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 c