// SPDX-License-Identifier: GPL-2.0
/*
 * zs.c: Serial port driver for IOASIC DECstations.
 *
 * Derived from drivers/sbus/char/sunserial.c by Paul Mackerras.
 * Derived from drivers/macintosh/macserial.c by Harald Koerfgen.
 *
 * DECstation changes
 * Copyright (C) 1998-2000 Harald Koerfgen
 * Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2007  Maciej W. Rozycki
 *
 * For the rest of the code the original Copyright applies:
 * Copyright (C) 1996 Paul Mackerras (Paul.Mackerras@cs.anu.edu.au)
 * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
 *
 *
 * Note: for IOASIC systems the wiring is as follows:
 *
 * mouse/keyboard:
 * DIN-7 MJ-4  signal        SCC
 * 2     1     TxD       <-  A.TxD
 * 3     4     RxD       ->  A.RxD
 *
 * EIA-232/EIA-423:
 * DB-25 MMJ-6 signal        SCC
 * 2     2     TxD       <-  B.TxD
 * 3     5     RxD       ->  B.RxD
 * 4           RTS       <- ~A.RTS
 * 5           CTS       -> ~B.CTS
 * 6     6     DSR       -> ~A.SYNC
 * 8           CD        -> ~B.DCD
 * 12          DSRS(DCE) -> ~A.CTS  (*)
 * 15          TxC       ->  B.TxC
 * 17          RxC       ->  B.RxC
 * 20    1     DTR       <- ~A.DTR
 * 22          RI        -> ~A.DCD
 * 23          DSRS(DTE) <- ~B.RTS
 *
 * (*) EIA-232 defines the signal at this pin to be SCD, while DSRS(DCE)
 *     is shared with DSRS(DTE) at pin 23.
 *
 * As you can immediately notice the wiring of the RTS, DTR and DSR signals
 * is a bit odd.  This makes the handling of port B unnecessarily
 * complicated and prevents the use of some automatic modes of operation.
 */

#include <linux/bug.h>
#include <linux/console.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/ioport.h>
#include <linux/irqflags.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/major.h>
#include <linux/platform_device.h>
#include <linux/serial.h>
#include <linux/serial_core.h>
#include <linux/spinlock.h>
#include <linux/sysrq.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/types.h>

#include <linux/atomic.h>

#include "zs.h"


MODULE_AUTHOR("Maciej W. Rozycki <macro@linux-mips.org>");
MODULE_DESCRIPTION("DECstation Z85C30 serial driver");
MODULE_LICENSE("GPL");


static char zs_name[] __initdata = "DECstation Z85C30 serial driver version ";
static char zs_version[] __initdata = "0.11";

/*
 * It would be nice to dynamically allocate everything that
 * depends on ZS_NUM_SCCS, so we could support any number of
 * Z85C30s, but for now...
 */
#define ZS_NUM_SCCS     2               /* Max # of ZS chips supported.  */
#define ZS_NUM_CHAN     2               /* 2 channels per chip.  */
#define ZS_CHAN_A       0               /* Index of the channel A.  */
#define ZS_CHAN_B       1               /* Index of the channel B.  */
#define ZS_CHAN_IO_SIZE 8               /* IOMEM space size.  */
#define ZS_CHAN_IO_STRIDE 4             /* Register alignment.  */
#define ZS_CHAN_IO_OFFSET 1             /* The SCC resides on the high byte
                                           of the 16-bit IOBUS.  */
#define ZS_CLOCK        7372800         /* Z85C30 PCLK input clock rate.  */

#define to_zport(uport) container_of(uport, struct zs_port, port)

static struct zs_scc zs_sccs[ZS_NUM_SCCS];
static struct uart_driver zs_reg;

/*
 * Set parameters in WR5, WR12, WR13 such as not to interfere
 * with the initial PROM-based console.  Otherwise any output
 * produced before the console handover would cause the system
 * firmware to hang (TxENAB) or produce rubbish (Tx8, B9600).
 */
static u8 zs_init_regs[ZS_NUM_REGS] __initdata = {
        0,                              /* write 0 */
        PAR_SPEC,                       /* write 1 */
        0,                              /* write 2 */
        0,                              /* write 3 */
        X16CLK | SB1,                   /* write 4 */
        Tx8 | TxENAB,                   /* write 5 */
        0, 0, 0,                        /* write 6, 7, 8 */
        MIE | DLC | NV,                 /* write 9 */
        NRZ,                            /* write 10 */
        TCBR | RCBR,                    /* write 11 */
        0x16, 0x00,                     /* BRG time constant, write 12 + 13 */
        BRSRC | BRENABL,                /* write 14 */
        0,                              /* write 15 */
};

/*
 * Debugging.
 */
#undef ZS_DEBUG_REGS


/*
 * Reading and writing Z85C30 registers.
 */
static void recovery_delay(void)
{
        udelay(2);
}

static u8 read_zsreg(struct zs_port *zport, int reg)
{
        void __iomem *control = zport->port.membase + ZS_CHAN_IO_OFFSET;
        u8 retval;

        if (reg != 0) {
                writeb(reg & 0xf, control);
                fast_iob();
                recovery_delay();
        }
        retval = readb(control);
        recovery_delay();
        return retval;
}

static void write_zsreg(struct zs_port *zport, int reg, u8 value)
{
        void __iomem *control = zport->port.membase + ZS_CHAN_IO_OFFSET;

        if (reg != 0) {
                writeb(reg & 0xf, control);
                fast_iob(); recovery_delay();
        }
        writeb(value, control);
        fast_iob();
        recovery_delay();
        return;
}

static u8 read_zsdata(struct zs_port *zport)
{
        void __iomem *data = zport->port.membase +
                             ZS_CHAN_IO_STRIDE + ZS_CHAN_IO_OFFSET;
        u8 retval;

        retval = readb(data);
        recovery_delay();
        return retval;
}

static void write_zsdata(struct zs_port *zport, u8 value)
{
        void __iomem *data = zport->port.membase +
                             ZS_CHAN_IO_STRIDE + ZS_CHAN_IO_OFFSET;

        writeb(value, data);
        fast_iob();
        recovery_delay();
        return;
}

#ifdef ZS_DEBUG_REGS
void zs_dump(void)
{
        struct zs_port *zport;
        int i, j;

        for (i = 0; i < ZS_NUM_SCCS * ZS_NUM_CHAN; i++) {
                zport = &zs_sccs[i / ZS_NUM_CHAN].zport[i % ZS_NUM_CHAN];

                if (!zport->scc)
                        continue;

                for (j = 0; j < 16; j++)
                        printk("W%-2d = 0x%02x\t", j, zport->regs[j]);
                printk("\n");
                for (j = 0; j < 16; j++)
                        printk("R%-2d = 0x%02x\t", j, read_zsreg(zport, j));
                printk("\n\n");
        }
}
#endif


static void zs_spin_lock_cond_irq(spinlock_t *lock, int irq)
{
        if (irq)
                spin_lock_irq(lock);
        else
                spin_lock(lock);
}

static void zs_spin_unlock_cond_irq(spinlock_t *lock, int irq)
{
        if (irq)
                spin_unlock_irq(lock);
        else
                spin_unlock(lock);
}

static int zs_receive_drain(struct zs_port *zport)
{
        int loops = 10000;

        while ((read_zsreg(zport, R0) & Rx_CH_AV) && --loops)
                read_zsdata(zport);
        return loops;
}

static int zs_transmit_drain(struct zs_port *zport, int irq)
{
        struct zs_scc *scc = zport->scc;
        int loops = 10000;

        while (!(read_zsreg(zport, R0) & Tx_BUF_EMP) && --loops) {
                zs_spin_unlock_cond_irq(&scc->zlock, irq);
                udelay(2);
                zs_spin_lock_cond_irq(&scc->zlock, irq);
        }
        return loops;
}

static int zs_line_drain(struct zs_port *zport, int irq)
{
        struct zs_scc *scc = zport->scc;
        int loops = 10000;

        while (!(read_zsreg(zport, R1) & ALL_SNT) && --loops) {
                zs_spin_unlock_cond_irq(&scc->zlock, irq);
                udelay(2);
                zs_spin_lock_cond_irq(&scc->zlock, irq);
        }
        return loops;
}


static void load_zsregs(struct zs_port *zport, u8 *regs, int irq)
{
        /* Let the current transmission finish.  */
        zs_line_drain(zport, irq);
        /* Load 'em up.  */
        write_zsreg(zport, R3, regs[3] & ~RxENABLE);
        write_zsreg(zport, R5, regs[5] & ~TxENAB);
        write_zsreg(zport, R4, regs[4]);
        write_zsreg(zport, R9, regs[9]);
        write_zsreg(zport, R1, regs[1]);
        write_zsreg(zport, R2, regs[2]);
        write_zsreg(zport, R10, regs[10]);
        write_zsreg(zport, R14, regs[14] & ~BRENABL);
        write_zsreg(zport, R11, regs[11]);
        write_zsreg(zport, R12, regs[12]);
        write_zsreg(zport, R13, regs[13]);
        write_zsreg(zport, R14, regs[14]);
        write_zsreg(zport, R15, regs[15]);
        if (regs[3] & RxENABLE)
                write_zsreg(zport, R3, regs[3]);
        if (regs[5] & TxENAB)
                write_zsreg(zport, R5, regs[5]);
        return;
}


/*
 * Status handling routines.
 */

/*
 * zs_tx_empty() -- get the transmitter empty status
 *
 * Purpose: Let user call ioctl() to get info when the UART physically
 *          is emptied.  On bus types like RS485, the transmitter must
 *          release the bus after transmitting.  This must be done when
 *          the transmit shift register is empty, not be done when the
 *          transmit holding register is empty.  This functionality
 *          allows an RS485 driver to be written in user space.
 */
static unsigned int zs_tx_empty(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        unsigned long flags;
        u8 status;

        spin_lock_irqsave(&scc->zlock, flags);
        status = read_zsreg(zport, R1);
        spin_unlock_irqrestore(&scc->zlock, flags);

        return status & ALL_SNT ? TIOCSER_TEMT : 0;
}

static unsigned int zs_raw_get_ab_mctrl(struct zs_port *zport_a,
                                        struct zs_port *zport_b)
{
        u8 status_a, status_b;
        unsigned int mctrl;

        status_a = read_zsreg(zport_a, R0);
        status_b = read_zsreg(zport_b, R0);

        mctrl = ((status_b & CTS) ? TIOCM_CTS : 0) |
                ((status_b & DCD) ? TIOCM_CAR : 0) |
                ((status_a & DCD) ? TIOCM_RNG : 0) |
                ((status_a & SYNC_HUNT) ? TIOCM_DSR : 0);

        return mctrl;
}

static unsigned int zs_raw_get_mctrl(struct zs_port *zport)
{
        struct zs_port *zport_a = &zport->scc->zport[ZS_CHAN_A];

        return zport != zport_a ? zs_raw_get_ab_mctrl(zport_a, zport) : 0;
}

static unsigned int zs_raw_xor_mctrl(struct zs_port *zport)
{
        struct zs_port *zport_a = &zport->scc->zport[ZS_CHAN_A];
        unsigned int mmask, mctrl, delta;
        u8 mask_a, mask_b;

        if (zport == zport_a)
                return 0;

        mask_a = zport_a->regs[15];
        mask_b = zport->regs[15];

        mmask = ((mask_b & CTSIE) ? TIOCM_CTS : 0) |
                ((mask_b & DCDIE) ? TIOCM_CAR : 0) |
                ((mask_a & DCDIE) ? TIOCM_RNG : 0) |
                ((mask_a & SYNCIE) ? TIOCM_DSR : 0);

        mctrl = zport->mctrl;
        if (mmask) {
                mctrl &= ~mmask;
                mctrl |= zs_raw_get_ab_mctrl(zport_a, zport) & mmask;
        }

        delta = mctrl ^ zport->mctrl;
        if (delta)
                zport->mctrl = mctrl;

        return delta;
}

static unsigned int zs_get_mctrl(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        unsigned int mctrl;

        spin_lock(&scc->zlock);
        mctrl = zs_raw_get_mctrl(zport);
        spin_unlock(&scc->zlock);

        return mctrl;
}

static void zs_set_mctrl(struct uart_port *uport, unsigned int mctrl)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        struct zs_port *zport_a = &scc->zport[ZS_CHAN_A];
        u8 oldloop, newloop;

        spin_lock(&scc->zlock);
        if (zport != zport_a) {
                if (mctrl & TIOCM_DTR)
                        zport_a->regs[5] |= DTR;
                else
                        zport_a->regs[5] &= ~DTR;
                if (mctrl & TIOCM_RTS)
                        zport_a->regs[5] |= RTS;
                else
                        zport_a->regs[5] &= ~RTS;
                write_zsreg(zport_a, R5, zport_a->regs[5]);
        }

        /* Rarely modified, so don't poke at hardware unless necessary. */
        oldloop = zport->regs[14];
        newloop = oldloop;
        if (mctrl & TIOCM_LOOP)
                newloop |= LOOPBAK;
        else
                newloop &= ~LOOPBAK;
        if (newloop != oldloop) {
                zport->regs[14] = newloop;
                write_zsreg(zport, R14, zport->regs[14]);
        }
        spin_unlock(&scc->zlock);
}

static void zs_raw_stop_tx(struct zs_port *zport)
{
        write_zsreg(zport, R0, RES_Tx_P);
        zport->tx_stopped = 1;
}

static void zs_stop_tx(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;

        spin_lock(&scc->zlock);
        zs_raw_stop_tx(zport);
        spin_unlock(&scc->zlock);
}

static void zs_raw_transmit_chars(struct zs_port *);

static void zs_start_tx(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;

        spin_lock(&scc->zlock);
        if (zport->tx_stopped) {
                zs_transmit_drain(zport, 0);
                zport->tx_stopped = 0;
                zs_raw_transmit_chars(zport);
        }
        spin_unlock(&scc->zlock);
}

static void zs_stop_rx(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        struct zs_port *zport_a = &scc->zport[ZS_CHAN_A];

        spin_lock(&scc->zlock);
        zport->regs[15] &= ~BRKIE;
        zport->regs[1] &= ~(RxINT_MASK | TxINT_ENAB);
        zport->regs[1] |= RxINT_DISAB;

        if (zport != zport_a) {
                /* A-side DCD tracks RI and SYNC tracks DSR.  */
                zport_a->regs[15] &= ~(DCDIE | SYNCIE);
                write_zsreg(zport_a, R15, zport_a->regs[15]);
                if (!(zport_a->regs[15] & BRKIE)) {
                        zport_a->regs[1] &= ~EXT_INT_ENAB;
                        write_zsreg(zport_a, R1, zport_a->regs[1]);
                }

                /* This-side DCD tracks DCD and CTS tracks CTS.  */
                zport->regs[15] &= ~(DCDIE | CTSIE);
                zport->regs[1] &= ~EXT_INT_ENAB;
        } else {
                /* DCD tracks RI and SYNC tracks DSR for the B side.  */
                if (!(zport->regs[15] & (DCDIE | SYNCIE)))
                        zport->regs[1] &= ~EXT_INT_ENAB;
        }

        write_zsreg(zport, R15, zport->regs[15]);
        write_zsreg(zport, R1, zport->regs[1]);
        spin_unlock(&scc->zlock);
}

static void zs_enable_ms(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        struct zs_port *zport_a = &scc->zport[ZS_CHAN_A];

        if (zport == zport_a)
                return;

        spin_lock(&scc->zlock);

        /* Clear Ext interrupts if not being handled already.  */
        if (!(zport_a->regs[1] & EXT_INT_ENAB))
                write_zsreg(zport_a, R0, RES_EXT_INT);

        /* A-side DCD tracks RI and SYNC tracks DSR.  */
        zport_a->regs[1] |= EXT_INT_ENAB;
        zport_a->regs[15] |= DCDIE | SYNCIE;

        /* This-side DCD tracks DCD and CTS tracks CTS.  */
        zport->regs[15] |= DCDIE | CTSIE;

        zs_raw_xor_mctrl(zport);

        write_zsreg(zport_a, R1, zport_a->regs[1]);
        write_zsreg(zport_a, R15, zport_a->regs[15]);
        write_zsreg(zport, R15, zport->regs[15]);
        spin_unlock(&scc->zlock);
}

static void zs_break_ctl(struct uart_port *uport, int break_state)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        unsigned long flags;

        spin_lock_irqsave(&scc->zlock, flags);
        if (break_state == -1)
                zport->regs[5] |= SND_BRK;
        else
                zport->regs[5] &= ~SND_BRK;
        write_zsreg(zport, R5, zport->regs[5]);
        spin_unlock_irqrestore(&scc->zlock, flags);
}


/*
 * Interrupt handling routines.
 */
#define Rx_BRK 0x0100                   /* BREAK event software flag.  */
#define Rx_SYS 0x0200                   /* SysRq event software flag.  */

static void zs_receive_chars(struct zs_port *zport)
{
        struct uart_port *uport = &zport->port;
        struct zs_scc *scc = zport->scc;
        struct uart_icount *icount;
        unsigned int avail, status;
        int count;
        u8 ch, flag;

        for (count = 16; count; count--) {
                spin_lock(&scc->zlock);
                avail = read_zsreg(zport, R0) & Rx_CH_AV;
                spin_unlock(&scc->zlock);
                if (!avail)
                        break;

                spin_lock(&scc->zlock);
                status = read_zsreg(zport, R1) & (Rx_OVR | FRM_ERR | PAR_ERR);
                ch = read_zsdata(zport);
                spin_unlock(&scc->zlock);

                flag = TTY_NORMAL;

                icount = &uport->icount;
                icount->rx++;

                /* Handle the null char got when BREAK is removed.  */
                if (!ch)
                        status |= zport->tty_break;
                if (unlikely(status &
                             (Rx_OVR | FRM_ERR | PAR_ERR | Rx_SYS | Rx_BRK))) {
                        zport->tty_break = 0;

                        /* Reset the error indication.  */
                        if (status & (Rx_OVR | FRM_ERR | PAR_ERR)) {
                                spin_lock(&scc->zlock);
                                write_zsreg(zport, R0, ERR_RES);
                                spin_unlock(&scc->zlock);
                        }

                        if (status & (Rx_SYS | Rx_BRK)) {
                                icount->brk++;
                                /* SysRq discards the null char.  */
                                if (status & Rx_SYS)
                                        continue;
                        } else if (status & FRM_ERR)
                                icount->frame++;
                        else if (status & PAR_ERR)
                                icount->parity++;
                        if (status & Rx_OVR)
                                icount->overrun++;

                        status &= uport->read_status_mask;
                        if (status & Rx_BRK)
                                flag = TTY_BREAK;
                        else if (status & FRM_ERR)
                                flag = TTY_FRAME;
                        else if (status & PAR_ERR)
                                flag = TTY_PARITY;
                }

                if (uart_handle_sysrq_char(uport, ch))
                        continue;

                uart_insert_char(uport, status, Rx_OVR, ch, flag);
        }

        tty_flip_buffer_push(&uport->state->port);
}

static void zs_raw_transmit_chars(struct zs_port *zport)
{
        struct tty_port *tport = &zport->port.state->port;
        unsigned char ch;

        /* XON/XOFF chars.  */
        if (zport->port.x_char) {
                write_zsdata(zport, zport->port.x_char);
                zport->port.icount.tx++;
                zport->port.x_char = 0;
                return;
        }

        /* If nothing to do or stopped or hardware stopped.  */
        if (uart_tx_stopped(&zport->port) ||
                        !uart_fifo_get(&zport->port, &ch)) {
                zs_raw_stop_tx(zport);
                return;
        }

        /* Send char.  */
        write_zsdata(zport, ch);

        if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
                uart_write_wakeup(&zport->port);

        /* Are we are done?  */
        if (kfifo_is_empty(&tport->xmit_fifo))
                zs_raw_stop_tx(zport);
}

static void zs_transmit_chars(struct zs_port *zport)
{
        struct zs_scc *scc = zport->scc;

        spin_lock(&scc->zlock);
        zs_raw_transmit_chars(zport);
        spin_unlock(&scc->zlock);
}

static void zs_status_handle(struct zs_port *zport, struct zs_port *zport_a)
{
        struct uart_port *uport = &zport->port;
        struct zs_scc *scc = zport->scc;
        unsigned int delta;
        u8 status, brk;

        spin_lock(&scc->zlock);

        /* Get status from Read Register 0.  */
        status = read_zsreg(zport, R0);

        if (zport->regs[15] & BRKIE) {
                brk = status & BRK_ABRT;
                if (brk && !zport->brk) {
                        spin_unlock(&scc->zlock);
                        if (uart_handle_break(uport))
                                zport->tty_break = Rx_SYS;
                        else
                                zport->tty_break = Rx_BRK;
                        spin_lock(&scc->zlock);
                }
                zport->brk = brk;
        }

        if (zport != zport_a) {
                delta = zs_raw_xor_mctrl(zport);
                spin_unlock(&scc->zlock);

                if (delta & TIOCM_CTS)
                        uart_handle_cts_change(uport,
                                               zport->mctrl & TIOCM_CTS);
                if (delta & TIOCM_CAR)
                        uart_handle_dcd_change(uport,
                                               zport->mctrl & TIOCM_CAR);
                if (delta & TIOCM_RNG)
                        uport->icount.rng++;
                if (delta & TIOCM_DSR)
                        uport->icount.dsr++;

                if (delta)
                        wake_up_interruptible(&uport->state->port.delta_msr_wait);

                spin_lock(&scc->zlock);
        }

        /* Clear the status condition...  */
        write_zsreg(zport, R0, RES_EXT_INT);

        spin_unlock(&scc->zlock);
}

/*
 * This is the Z85C30 driver's generic interrupt routine.
 */
static irqreturn_t zs_interrupt(int irq, void *dev_id)
{
        struct zs_scc *scc = dev_id;
        struct zs_port *zport_a = &scc->zport[ZS_CHAN_A];
        struct zs_port *zport_b = &scc->zport[ZS_CHAN_B];
        irqreturn_t status = IRQ_NONE;
        u8 zs_intreg;
        int count;

        /*
         * NOTE: The read register 3, which holds the irq status,
         *       does so for both channels on each chip.  Although
         *       the status value itself must be read from the A
         *       channel and is only valid when read from channel A.
         *       Yes... broken hardware...
         */
        for (count = 16; count; count--) {
                spin_lock(&scc->zlock);
                zs_intreg = read_zsreg(zport_a, R3);
                spin_unlock(&scc->zlock);
                if (!zs_intreg)
                        break;

                /*
                 * We do not like losing characters, so we prioritise
                 * interrupt sources a little bit differently than
                 * the SCC would, was it allowed to.
                 */
                if (zs_intreg & CHBRxIP)
                        zs_receive_chars(zport_b);
                if (zs_intreg & CHARxIP)
                        zs_receive_chars(zport_a);
                if (zs_intreg & CHBEXT)
                        zs_status_handle(zport_b, zport_a);
                if (zs_intreg & CHAEXT)
                        zs_status_handle(zport_a, zport_a);
                if (zs_intreg & CHBTxIP)
                        zs_transmit_chars(zport_b);
                if (zs_intreg & CHATxIP)
                        zs_transmit_chars(zport_a);

                status = IRQ_HANDLED;
        }

        return status;
}


/*
 * Finally, routines used to initialize the serial port.
 */
static int zs_startup(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        unsigned long flags;
        int irq_guard;
        int ret;

        irq_guard = atomic_add_return(1, &scc->irq_guard);
        if (irq_guard == 1) {
                ret = request_irq(zport->port.irq, zs_interrupt,
                                  IRQF_SHARED, "scc", scc);
                if (ret) {
                        atomic_add(-1, &scc->irq_guard);
                        printk(KERN_ERR "zs: can't get irq %d\n",
                               zport->port.irq);
                        return ret;
                }
        }

        spin_lock_irqsave(&scc->zlock, flags);

        /* Clear the receive FIFO.  */
        zs_receive_drain(zport);

        /* Clear the interrupt registers.  */
        write_zsreg(zport, R0, ERR_RES);
        write_zsreg(zport, R0, RES_Tx_P);
        /* But Ext only if not being handled already.  */
        if (!(zport->regs[1] & EXT_INT_ENAB))
                write_zsreg(zport, R0, RES_EXT_INT);

        /* Finally, enable sequencing and interrupts.  */
        zport->regs[1] &= ~RxINT_MASK;
        zport->regs[1] |= RxINT_ALL | TxINT_ENAB | EXT_INT_ENAB;
        zport->regs[3] |= RxENABLE;
        zport->regs[15] |= BRKIE;
        write_zsreg(zport, R1, zport->regs[1]);
        write_zsreg(zport, R3, zport->regs[3]);
        write_zsreg(zport, R5, zport->regs[5]);
        write_zsreg(zport, R15, zport->regs[15]);

        /* Record the current state of RR0.  */
        zport->mctrl = zs_raw_get_mctrl(zport);
        zport->brk = read_zsreg(zport, R0) & BRK_ABRT;

        zport->tx_stopped = 1;

        spin_unlock_irqrestore(&scc->zlock, flags);

        return 0;
}

static void zs_shutdown(struct uart_port *uport)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        unsigned long flags;
        int irq_guard;

        spin_lock_irqsave(&scc->zlock, flags);

        zport->regs[3] &= ~RxENABLE;
        write_zsreg(zport, R5, zport->regs[5]);
        write_zsreg(zport, R3, zport->regs[3]);

        spin_unlock_irqrestore(&scc->zlock, flags);

        irq_guard = atomic_add_return(-1, &scc->irq_guard);
        if (!irq_guard)
                free_irq(zport->port.irq, scc);
}


static void zs_reset(struct zs_port *zport)
{
        struct zs_port *zport_a = &zport->scc->zport[ZS_CHAN_A];
        struct zs_scc *scc = zport->scc;
        int irq;
        unsigned long flags;

        spin_lock_irqsave(&scc->zlock, flags);
        irq = !irqs_disabled_flags(flags);

        /* Reset the pointer first, just in case...  */
        read_zsreg(zport, R0);
        /* And let the current transmission finish.  */
        zs_line_drain(zport, irq);
        write_zsreg(zport, R9, zport == zport_a ? CHRA : CHRB);
        udelay(10);
        write_zsreg(zport, R9, 0);

        load_zsregs(zport, zport->regs, irq);
        spin_unlock_irqrestore(&scc->zlock, flags);
}

static void zs_set_termios(struct uart_port *uport, struct ktermios *termios,
                           const struct ktermios *old_termios)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        struct zs_port *zport_a = &scc->zport[ZS_CHAN_A];
        int irq;
        unsigned int baud, brg;
        unsigned long flags;

        spin_lock_irqsave(&scc->zlock, flags);
        irq = !irqs_disabled_flags(flags);

        /* Byte size.  */
        zport->regs[3] &= ~RxNBITS_MASK;
        zport->regs[5] &= ~TxNBITS_MASK;
        switch (termios->c_cflag & CSIZE) {
        case CS5:
                zport->regs[3] |= Rx5;
                zport->regs[5] |= Tx5;
                break;
        case CS6:
                zport->regs[3] |= Rx6;
                zport->regs[5] |= Tx6;
                break;
        case CS7:
                zport->regs[3] |= Rx7;
                zport->regs[5] |= Tx7;
                break;
        case CS8:
        default:
                zport->regs[3] |= Rx8;
                zport->regs[5] |= Tx8;
                break;
        }

        /* Parity and stop bits.  */
        zport->regs[4] &= ~(XCLK_MASK | SB_MASK | PAR_ENA | PAR_EVEN);
        if (termios->c_cflag & CSTOPB)
                zport->regs[4] |= SB2;
        else
                zport->regs[4] |= SB1;
        if (termios->c_cflag & PARENB)
                zport->regs[4] |= PAR_ENA;
        if (!(termios->c_cflag & PARODD))
                zport->regs[4] |= PAR_EVEN;
        switch (zport->clk_mode) {
        case 64:
                zport->regs[4] |= X64CLK;
                break;
        case 32:
                zport->regs[4] |= X32CLK;
                break;
        case 16:
                zport->regs[4] |= X16CLK;
                break;
        case 1:
                zport->regs[4] |= X1CLK;
                break;
        default:
                BUG();
        }

        baud = uart_get_baud_rate(uport, termios, old_termios, 0,
                                  uport->uartclk / zport->clk_mode / 4);

        brg = ZS_BPS_TO_BRG(baud, uport->uartclk / zport->clk_mode);
        zport->regs[12] = brg & 0xff;
        zport->regs[13] = (brg >> 8) & 0xff;

        uart_update_timeout(uport, termios->c_cflag, baud);

        uport->read_status_mask = Rx_OVR;
        if (termios->c_iflag & INPCK)
                uport->read_status_mask |= FRM_ERR | PAR_ERR;
        if (termios->c_iflag & (IGNBRK | BRKINT | PARMRK))
                uport->read_status_mask |= Rx_BRK;

        uport->ignore_status_mask = 0;
        if (termios->c_iflag & IGNPAR)
                uport->ignore_status_mask |= FRM_ERR | PAR_ERR;
        if (termios->c_iflag & IGNBRK) {
                uport->ignore_status_mask |= Rx_BRK;
                if (termios->c_iflag & IGNPAR)
                        uport->ignore_status_mask |= Rx_OVR;
        }

        if (termios->c_cflag & CREAD)
                zport->regs[3] |= RxENABLE;
        else
                zport->regs[3] &= ~RxENABLE;

        if (zport != zport_a) {
                if (!(termios->c_cflag & CLOCAL)) {
                        zport->regs[15] |= DCDIE;
                } else
                        zport->regs[15] &= ~DCDIE;
                if (termios->c_cflag & CRTSCTS) {
                        zport->regs[15] |= CTSIE;
                } else
                        zport->regs[15] &= ~CTSIE;
                zs_raw_xor_mctrl(zport);
        }

        /* Load up the new values.  */
        load_zsregs(zport, zport->regs, irq);

        spin_unlock_irqrestore(&scc->zlock, flags);
}


static const char *zs_type(struct uart_port *uport)
{
        return "Z85C30 SCC";
}

static void zs_release_port(struct uart_port *uport)
{
        iounmap(uport->membase);
        uport->membase = NULL;
        release_mem_region(uport->mapbase, ZS_CHAN_IO_SIZE);
}

static int zs_map_port(struct uart_port *uport)
{
        if (!uport->membase)
                uport->membase = ioremap(uport->mapbase,
                                                 ZS_CHAN_IO_SIZE);
        if (!uport->membase) {
                printk(KERN_ERR "zs: Cannot map MMIO\n");
                return -ENOMEM;
        }
        return 0;
}

static int zs_request_port(struct uart_port *uport)
{
        int ret;

        if (!request_mem_region(uport->mapbase, ZS_CHAN_IO_SIZE, "scc")) {
                printk(KERN_ERR "zs: Unable to reserve MMIO resource\n");
                return -EBUSY;
        }
        ret = zs_map_port(uport);
        if (ret) {
                release_mem_region(uport->mapbase, ZS_CHAN_IO_SIZE);
                return ret;
        }
        return 0;
}

static void zs_config_port(struct uart_port *uport, int flags)
{
        struct zs_port *zport = to_zport(uport);

        if (flags & UART_CONFIG_TYPE) {
                if (zs_request_port(uport))
                        return;

                uport->type = PORT_ZS;

                zs_reset(zport);
        }
}

static int zs_verify_port(struct uart_port *uport, struct serial_struct *ser)
{
        struct zs_port *zport = to_zport(uport);
        int ret = 0;

        if (ser->type != PORT_UNKNOWN && ser->type != PORT_ZS)
                ret = -EINVAL;
        if (ser->irq != uport->irq)
                ret = -EINVAL;
        if (ser->baud_base != uport->uartclk / zport->clk_mode / 4)
                ret = -EINVAL;
        return ret;
}


static const struct uart_ops zs_ops = {
        .tx_empty       = zs_tx_empty,
        .set_mctrl      = zs_set_mctrl,
        .get_mctrl      = zs_get_mctrl,
        .stop_tx        = zs_stop_tx,
        .start_tx       = zs_start_tx,
        .stop_rx        = zs_stop_rx,
        .enable_ms      = zs_enable_ms,
        .break_ctl      = zs_break_ctl,
        .startup        = zs_startup,
        .shutdown       = zs_shutdown,
        .set_termios    = zs_set_termios,
        .type           = zs_type,
        .release_port   = zs_release_port,
        .request_port   = zs_request_port,
        .config_port    = zs_config_port,
        .verify_port    = zs_verify_port,
};

/*
 * Initialize Z85C30 port structures.
 */
static int __init zs_probe(struct platform_device *pdev)
{
        struct resource *mem_resource, *irq_resource;
        int chip, side;
        int i;

        mem_resource = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        irq_resource = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
        if (!mem_resource || !irq_resource)
                return -ENODEV;

        chip = pdev->id;
        spin_lock_init(&zs_sccs[chip].zlock);
        for (side = 0; side < ZS_NUM_CHAN; side++) {
                struct zs_port *zport = &zs_sccs[chip].zport[side];
                struct uart_port *uport = &zport->port;

                zport->scc      = &zs_sccs[chip];
                zport->clk_mode = 16;

                uport->dev      = &pdev->dev;
                uport->has_sysrq = IS_ENABLED(CONFIG_SERIAL_ZS_CONSOLE);
                uport->irq      = irq_resource->start;
                uport->uartclk  = ZS_CLOCK;
                uport->fifosize = 1;
                uport->iotype   = UPIO_MEM;
                uport->flags    = UPF_BOOT_AUTOCONF;
                uport->ops      = &zs_ops;
                uport->line     = chip * ZS_NUM_CHAN + side;
                uport->mapbase  = mem_resource->start +
                                  (side ^ ZS_CHAN_B) * ZS_CHAN_IO_SIZE;

                for (i = 0; i < ZS_NUM_REGS; i++)
                        zport->regs[i] = zs_init_regs[i];

                if (uart_add_one_port(&zs_reg, uport))
                        uport->dev = NULL;
        }

        return 0;
}

static void __exit zs_remove(struct platform_device *pdev)
{
        int chip, side;

        chip = pdev->id;
        for (side = ZS_NUM_CHAN - 1; side >= 0; side--) {
                struct zs_port *zport = &zs_sccs[chip].zport[side];
                struct uart_port *uport = &zport->port;

                if (uport->dev)
                        uart_remove_one_port(&zs_reg, uport);
        }
}


#ifdef CONFIG_SERIAL_ZS_CONSOLE
static void zs_console_putchar(struct uart_port *uport, unsigned char ch)
{
        struct zs_port *zport = to_zport(uport);
        struct zs_scc *scc = zport->scc;
        int irq;
        unsigned long flags;

        spin_lock_irqsave(&scc->zlock, flags);
        irq = !irqs_disabled_flags(flags);
        if (zs_transmit_drain(zport, irq))
                write_zsdata(zport, ch);
        spin_unlock_irqrestore(&scc->zlock, flags);
}

/*
 * Print a string to the serial port trying not to disturb
 * any possible real use of the port...
 */
static void zs_console_write(struct console *co, const char *s,
                             unsigned int count)
{
        int chip = co->index / ZS_NUM_CHAN, side = co->index % ZS_NUM_CHAN;
        struct zs_port *zport = &zs_sccs[chip].zport[side];
        struct zs_scc *scc = zport->scc;
        unsigned long flags;
        u8 txint, txenb;
        int irq;

        /* Disable transmit interrupts and enable the transmitter. */
        spin_lock_irqsave(&scc->zlock, flags);
        txint = zport->regs[1];
        txenb = zport->regs[5];
        if (txint & TxINT_ENAB) {
                zport->regs[1] = txint & ~TxINT_ENAB;
                write_zsreg(zport, R1, zport->regs[1]);
        }
        if (!(txenb & TxENAB)) {
                zport->regs[5] = txenb | TxENAB;
                write_zsreg(zport, R5, zport->regs[5]);
        }
        spin_unlock_irqrestore(&scc->zlock, flags);

        uart_console_write(&zport->port, s, count, zs_console_putchar);

        /* Restore transmit interrupts and the transmitter enable. */
        spin_lock_irqsave(&scc->zlock, flags);
        irq = !irqs_disabled_flags(flags);
        zs_line_drain(zport, irq);
        if (!(txenb & TxENAB)) {
                zport->regs[5] &= ~TxENAB;
                write_zsreg(zport, R5, zport->regs[5]);
        }
        if (txint & TxINT_ENAB) {
                zport->regs[1] |= TxINT_ENAB;
                write_zsreg(zport, R1, zport->regs[1]);

                /* Resume any transmission as the TxIP bit won't be set.  */
                if (!zport->tx_stopped)
                        zs_raw_transmit_chars(zport);
        }
        spin_unlock_irqrestore(&scc->zlock, flags);
}

/*
 * Setup serial console baud/bits/parity.  We do two things here:
 * - construct a cflag setting for the first uart_open()
 * - initialise the serial port
 * Return non-zero if we didn't find a serial port.
 */
static int __init zs_console_setup(struct console *co, char *options)
{
        int chip = co->index / ZS_NUM_CHAN, side = co->index % ZS_NUM_CHAN;
        struct zs_port *zport = &zs_sccs[chip].zport[side];
        struct uart_port *uport = &zport->port;
        int baud = 9600;
        int bits = 8;
        int parity = 'n';
        int flow = 'n';

        if (!zport->scc)
                return -ENODEV;
        if (options)
                uart_parse_options(options, &baud, &parity, &bits, &flow);
        return uart_set_options(uport, co, baud, parity, bits, flow);
}

static struct console zs_console = {
        .name   = "ttyS",
        .write  = zs_console_write,
        .device = uart_console_device,
        .setup  = zs_console_setup,
        .flags  = CON_PRINTBUFFER,
        .index  = -1,
        .data   = &zs_reg,
};

#define SERIAL_ZS_CONSOLE       &zs_console
#else
#define SERIAL_ZS_CONSOLE       NULL
#endif /* CONFIG_SERIAL_ZS_CONSOLE */

static struct uart_driver zs_reg = {
        .owner                  = THIS_MODULE,
        .driver_name            = "serial_zs",
        .dev_name               = "ttyS",
        .major                  = TTY_MAJOR,
        .minor                  = 64,
        .nr                     = ZS_NUM_SCCS * ZS_NUM_CHAN,
        .cons                   = SERIAL_ZS_CONSOLE,
};

static struct platform_driver zs_driver = {
        .remove = __exit_p(zs_remove),
        .driver = { .name = "zs" },
};

/* zs_init inits the driver. */
static int __init zs_init(void)
{
        int ret;

        pr_info("%s%s\n", zs_name, zs_version);

        ret = uart_register_driver(&zs_reg);
        if (ret)
                return ret;
        ret = platform_driver_probe(&zs_driver, zs_probe);
        if (ret)
                uart_unregister_driver(&zs_reg);

        return ret;
}

static void __exit zs_exit(void)
{
        platform_driver_unregister(&zs_driver);
        uart_unregister_driver(&zs_reg);
}

module_init(zs_init);
module_exit(zs_exit);