linux-imx

// 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;

    }

}