// SPDX-License-Identifier: GPL-2.0+
/*
 * i2c-algo-bit.c: i2c driver algorithms for bit-shift adapters
 *
 *   Copyright (C) 1995-2000 Simon G. Vogl
 *
 * With some changes from Frodo Looijaard <frodol@dds.nl>, Kyösti Mälkki
 * <kmalkki@cc.hut.fi> and Jean Delvare <jdelvare@suse.de>
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/i2c.h>
#include <linux/i2c-algo-bit.h>


/* ----- global defines ----------------------------------------------- */

#ifdef DEBUG
#define bit_dbg(level, dev, format, args...) \
        do { \
                if (i2c_debug >= level) \
                        dev_dbg(dev, format, ##args); \
        } while (0)
#else
#define bit_dbg(level, dev, format, args...) \
        do {} while (0)
#endif /* DEBUG */

/* ----- global variables --------------------------------------------- */

static int bit_test;    /* see if the line-setting functions work       */
module_param(bit_test, int, S_IRUGO);
MODULE_PARM_DESC(bit_test, "lines testing - 0 off; 1 report; 2 fail if stuck");

#ifdef DEBUG
static int i2c_debug = 1;
module_param(i2c_debug, int, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(i2c_debug,
                 "debug level - 0 off; 1 normal; 2 verbose; 3 very verbose");
#endif

/* --- setting states on the bus with the right timing: --------------- */

#define setsda(adap, val)       adap->setsda(adap->data, val)
#define setscl(adap, val)       adap->setscl(adap->data, val)
#define getsda(adap)            adap->getsda(adap->data)
#define getscl(adap)            adap->getscl(adap->data)

static inline void sdalo(struct i2c_algo_bit_data *adap)
{
        setsda(adap, 0);
        udelay((adap->udelay + 1) / 2);
}

static inline void sdahi(struct i2c_algo_bit_data *adap)
{
        setsda(adap, 1);
        udelay((adap->udelay + 1) / 2);
}

static inline void scllo(struct i2c_algo_bit_data *adap)
{
        setscl(adap, 0);
        udelay(adap->udelay / 2);
}

/*
 * Raise scl line, and do checking for delays. This is necessary for slower
 * devices.
 */
static int sclhi(struct i2c_algo_bit_data *adap)
{
        unsigned long start;

        setscl(adap, 1);

        /* Not all adapters have scl sense line... */
        if (!adap->getscl)
                goto done;

        start = jiffies;
        while (!getscl(adap)) {
                /* This hw knows how to read the clock line, so we wait
                 * until it actually gets high.  This is safer as some
                 * chips may hold it low ("clock stretching") while they
                 * are processing data internally.
                 */
                if (time_after(jiffies, start + adap->timeout)) {
                        /* Test one last time, as we may have been preempted
                         * between last check and timeout test.
                         */
                        if (getscl(adap))
                                break;
                        return -ETIMEDOUT;
                }
                cpu_relax();
        }
#ifdef DEBUG
        if (jiffies != start && i2c_debug >= 3)
                pr_debug("i2c-algo-bit: needed %ld jiffies for SCL to go high\n",
                         jiffies - start);
#endif

done:
        udelay(adap->udelay);
        return 0;
}


/* --- other auxiliary functions -------------------------------------- */
static void i2c_start(struct i2c_algo_bit_data *adap)
{
        /* assert: scl, sda are high */
        setsda(adap, 0);
        udelay(adap->udelay);
        scllo(adap);
}

static void i2c_repstart(struct i2c_algo_bit_data *adap)
{
        /* assert: scl is low */
        sdahi(adap);
        sclhi(adap);
        setsda(adap, 0);
        udelay(adap->udelay);
        scllo(adap);
}


static void i2c_stop(struct i2c_algo_bit_data *adap)
{
        /* assert: scl is low */
        sdalo(adap);
        sclhi(adap);
        setsda(adap, 1);
        udelay(adap->udelay);
}



/* send a byte without start cond., look for arbitration,
   check ackn. from slave */
/* returns:
 * 1 if the device acknowledged
 * 0 if the device did not ack
 * -ETIMEDOUT if an error occurred (while raising the scl line)
 */
static int i2c_outb(struct i2c_adapter *i2c_adap, unsigned char c)
{
        int i;
        int sb;
        int ack;
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;

        /* assert: scl is low */
        for (i = 7; i >= 0; i--) {
                sb = (c >> i) & 1;
                setsda(adap, sb);
                udelay((adap->udelay + 1) / 2);
                if (sclhi(adap) < 0) { /* timed out */
                        bit_dbg(1, &i2c_adap->dev,
                                "i2c_outb: 0x%02x, timeout at bit #%d\n",
                                (int)c, i);
                        return -ETIMEDOUT;
                }
                /* FIXME do arbitration here:
                 * if (sb && !getsda(adap)) -> ouch! Get out of here.
                 *
                 * Report a unique code, so higher level code can retry
                 * the whole (combined) message and *NOT* issue STOP.
                 */
                scllo(adap);
        }
        sdahi(adap);
        if (sclhi(adap) < 0) { /* timeout */
                bit_dbg(1, &i2c_adap->dev,
                        "i2c_outb: 0x%02x, timeout at ack\n", (int)c);
                return -ETIMEDOUT;
        }

        /* read ack: SDA should be pulled down by slave, or it may
         * NAK (usually to report problems with the data we wrote).
         */
        ack = !getsda(adap);    /* ack: sda is pulled low -> success */
        bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
                ack ? "A" : "NA");

        scllo(adap);
        return ack;
        /* assert: scl is low (sda undef) */
}


static int i2c_inb(struct i2c_adapter *i2c_adap)
{
        /* read byte via i2c port, without start/stop sequence  */
        /* acknowledge is sent in i2c_read.                     */
        int i;
        unsigned char indata = 0;
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;

        /* assert: scl is low */
        sdahi(adap);
        for (i = 0; i < 8; i++) {
                if (sclhi(adap) < 0) { /* timeout */
                        bit_dbg(1, &i2c_adap->dev,
                                "i2c_inb: timeout at bit #%d\n",
                                7 - i);
                        return -ETIMEDOUT;
                }
                indata *= 2;
                if (getsda(adap))
                        indata |= 0x01;
                setscl(adap, 0);
                udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
        }
        /* assert: scl is low */
        return indata;
}

/*
 * Sanity check for the adapter hardware - check the reaction of
 * the bus lines only if it seems to be idle.
 */
static int test_bus(struct i2c_adapter *i2c_adap)
{
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
        const char *name = i2c_adap->name;
        int scl, sda, ret;

        if (adap->pre_xfer) {
                ret = adap->pre_xfer(i2c_adap);
                if (ret < 0)
                        return -ENODEV;
        }

        if (adap->getscl == NULL)
                pr_info("%s: Testing SDA only, SCL is not readable\n", name);

        sda = getsda(adap);
        scl = (adap->getscl == NULL) ? 1 : getscl(adap);
        if (!scl || !sda) {
                printk(KERN_WARNING
                       "%s: bus seems to be busy (scl=%d, sda=%d)\n",
                       name, scl, sda);
                goto bailout;
        }

        sdalo(adap);
        sda = getsda(adap);
        scl = (adap->getscl == NULL) ? 1 : getscl(adap);
        if (sda) {
                printk(KERN_WARNING "%s: SDA stuck high!\n", name);
                goto bailout;
        }
        if (!scl) {
                printk(KERN_WARNING
                       "%s: SCL unexpected low while pulling SDA low!\n",
                       name);
                goto bailout;
        }

        sdahi(adap);
        sda = getsda(adap);
        scl = (adap->getscl == NULL) ? 1 : getscl(adap);
        if (!sda) {
                printk(KERN_WARNING "%s: SDA stuck low!\n", name);
                goto bailout;
        }
        if (!scl) {
                printk(KERN_WARNING
                       "%s: SCL unexpected low while pulling SDA high!\n",
                       name);
                goto bailout;
        }

        scllo(adap);
        sda = getsda(adap);
        scl = (adap->getscl == NULL) ? 0 : getscl(adap);
        if (scl) {
                printk(KERN_WARNING "%s: SCL stuck high!\n", name);
                goto bailout;
        }
        if (!sda) {
                printk(KERN_WARNING
                       "%s: SDA unexpected low while pulling SCL low!\n",
                       name);
                goto bailout;
        }

        sclhi(adap);
        sda = getsda(adap);
        scl = (adap->getscl == NULL) ? 1 : getscl(adap);
        if (!scl) {
                printk(KERN_WARNING "%s: SCL stuck low!\n", name);
                goto bailout;
        }
        if (!sda) {
                printk(KERN_WARNING
                       "%s: SDA unexpected low while pulling SCL high!\n",
                       name);
                goto bailout;
        }

        if (adap->post_xfer)
                adap->post_xfer(i2c_adap);

        pr_info("%s: Test OK\n", name);
        return 0;
bailout:
        sdahi(adap);
        sclhi(adap);

        if (adap->post_xfer)
                adap->post_xfer(i2c_adap);

        return -ENODEV;
}

/* ----- Utility functions
 */

/* try_address tries to contact a chip for a number of
 * times before it gives up.
 * return values:
 * 1 chip answered
 * 0 chip did not answer
 * -x transmission error
 */
static int try_address(struct i2c_adapter *i2c_adap,
                       unsigned char addr, int retries)
{
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
        int i, ret = 0;

        for (i = 0; i <= retries; i++) {
                ret = i2c_outb(i2c_adap, addr);
                if (ret == 1 || i == retries)
                        break;
                bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
                i2c_stop(adap);
                udelay(adap->udelay);
                yield();
                bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
                i2c_start(adap);
        }
        if (i && ret)
                bit_dbg(1, &i2c_adap->dev,
                        "Used %d tries to %s client at 0x%02x: %s\n", i + 1,
                        addr & 1 ? "read from" : "write to", addr >> 1,
                        ret == 1 ? "success" : "failed, timeout?");
        return ret;
}

static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
        const unsigned char *temp = msg->buf;
        int count = msg->len;
        unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
        int retval;
        int wrcount = 0;

        while (count > 0) {
                retval = i2c_outb(i2c_adap, *temp);

                /* OK/ACK; or ignored NAK */
                if ((retval > 0) || (nak_ok && (retval == 0))) {
                        count--;
                        temp++;
                        wrcount++;

                /* A slave NAKing the master means the slave didn't like
                 * something about the data it saw.  For example, maybe
                 * the SMBus PEC was wrong.
                 */
                } else if (retval == 0) {
                        dev_err(&i2c_adap->dev, "sendbytes: NAK bailout.\n");
                        return -EIO;

                /* Timeout; or (someday) lost arbitration
                 *
                 * FIXME Lost ARB implies retrying the transaction from
                 * the first message, after the "winning" master issues
                 * its STOP.  As a rule, upper layer code has no reason
                 * to know or care about this ... it is *NOT* an error.
                 */
                } else {
                        dev_err(&i2c_adap->dev, "sendbytes: error %d\n",
                                        retval);
                        return retval;
                }
        }
        return wrcount;
}

static int acknak(struct i2c_adapter *i2c_adap, int is_ack)
{
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;

        /* assert: sda is high */
        if (is_ack)             /* send ack */
                setsda(adap, 0);
        udelay((adap->udelay + 1) / 2);
        if (sclhi(adap) < 0) {  /* timeout */
                dev_err(&i2c_adap->dev, "readbytes: ack/nak timeout\n");
                return -ETIMEDOUT;
        }
        scllo(adap);
        return 0;
}

static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
        int inval;
        int rdcount = 0;        /* counts bytes read */
        unsigned char *temp = msg->buf;
        int count = msg->len;
        const unsigned flags = msg->flags;

        while (count > 0) {
                inval = i2c_inb(i2c_adap);
                if (inval >= 0) {
                        *temp = inval;
                        rdcount++;
                } else {   /* read timed out */
                        break;
                }

                temp++;
                count--;

                /* Some SMBus transactions require that we receive the
                   transaction length as the first read byte. */
                if (rdcount == 1 && (flags & I2C_M_RECV_LEN)) {
                        if (inval <= 0 || inval > I2C_SMBUS_BLOCK_MAX) {
                                if (!(flags & I2C_M_NO_RD_ACK))
                                        acknak(i2c_adap, 0);
                                dev_err(&i2c_adap->dev,
                                        "readbytes: invalid block length (%d)\n",
                                        inval);
                                return -EPROTO;
                        }
                        /* The original count value accounts for the extra
                           bytes, that is, either 1 for a regular transaction,
                           or 2 for a PEC transaction. */
                        count += inval;
                        msg->len += inval;
                }

                bit_dbg(2, &i2c_adap->dev, "readbytes: 0x%02x %s\n",
                        inval,
                        (flags & I2C_M_NO_RD_ACK)
                                ? "(no ack/nak)"
                                : (count ? "A" : "NA"));

                if (!(flags & I2C_M_NO_RD_ACK)) {
                        inval = acknak(i2c_adap, count);
                        if (inval < 0)
                                return inval;
                }
        }
        return rdcount;
}

/* doAddress initiates the transfer by generating the start condition (in
 * try_address) and transmits the address in the necessary format to handle
 * reads, writes as well as 10bit-addresses.
 * returns:
 *  0 everything went okay, the chip ack'ed, or IGNORE_NAK flag was set
 * -x an error occurred (like: -ENXIO if the device did not answer, or
 *      -ETIMEDOUT, for example if the lines are stuck...)
 */
static int bit_doAddress(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
        unsigned short flags = msg->flags;
        unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;

        unsigned char addr;
        int ret, retries;

        retries = nak_ok ? 0 : i2c_adap->retries;

        if (flags & I2C_M_TEN) {
                /* a ten bit address */
                addr = 0xf0 | ((msg->addr >> 7) & 0x06);
                bit_dbg(2, &i2c_adap->dev, "addr0: %d\n", addr);
                /* try extended address code...*/
                ret = try_address(i2c_adap, addr, retries);
                if ((ret != 1) && !nak_ok)  {
                        dev_err(&i2c_adap->dev,
                                "died at extended address code\n");
                        return -ENXIO;
                }
                /* the remaining 8 bit address */
                ret = i2c_outb(i2c_adap, msg->addr & 0xff);
                if ((ret != 1) && !nak_ok) {
                        /* the chip did not ack / xmission error occurred */
                        dev_err(&i2c_adap->dev, "died at 2nd address code\n");
                        return -ENXIO;
                }
                if (flags & I2C_M_RD) {
                        bit_dbg(3, &i2c_adap->dev,
                                "emitting repeated start condition\n");
                        i2c_repstart(adap);
                        /* okay, now switch into reading mode */
                        addr |= 0x01;
                        ret = try_address(i2c_adap, addr, retries);
                        if ((ret != 1) && !nak_ok) {
                                dev_err(&i2c_adap->dev,
                                        "died at repeated address code\n");
                                return -EIO;
                        }
                }
        } else {                /* normal 7bit address  */
                addr = i2c_8bit_addr_from_msg(msg);
                if (flags & I2C_M_REV_DIR_ADDR)
                        addr ^= 1;
                ret = try_address(i2c_adap, addr, retries);
                if ((ret != 1) && !nak_ok)
                        return -ENXIO;
        }

        return 0;
}

static int bit_xfer(struct i2c_adapter *i2c_adap,
                    struct i2c_msg msgs[], int num)
{
        struct i2c_msg *pmsg;
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
        int i, ret;
        unsigned short nak_ok;

        if (adap->pre_xfer) {
                ret = adap->pre_xfer(i2c_adap);
                if (ret < 0)
                        return ret;
        }

        bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
        i2c_start(adap);
        for (i = 0; i < num; i++) {
                pmsg = &msgs[i];
                nak_ok = pmsg->flags & I2C_M_IGNORE_NAK;
                if (!(pmsg->flags & I2C_M_NOSTART)) {
                        if (i) {
                                if (msgs[i - 1].flags & I2C_M_STOP) {
                                        bit_dbg(3, &i2c_adap->dev,
                                                "emitting enforced stop/start condition\n");
                                        i2c_stop(adap);
                                        i2c_start(adap);
                                } else {
                                        bit_dbg(3, &i2c_adap->dev,
                                                "emitting repeated start condition\n");
                                        i2c_repstart(adap);
                                }
                        }
                        ret = bit_doAddress(i2c_adap, pmsg);
                        if ((ret != 0) && !nak_ok) {
                                bit_dbg(1, &i2c_adap->dev,
                                        "NAK from device addr 0x%02x msg #%d\n",
                                        msgs[i].addr, i);
                                goto bailout;
                        }
                }
                if (pmsg->flags & I2C_M_RD) {
                        /* read bytes into buffer*/
                        ret = readbytes(i2c_adap, pmsg);
                        if (ret >= 1)
                                bit_dbg(2, &i2c_adap->dev, "read %d byte%s\n",
                                        ret, ret == 1 ? "" : "s");
                        if (ret < pmsg->len) {
                                if (ret >= 0)
                                        ret = -EIO;
                                goto bailout;
                        }
                } else {
                        /* write bytes from buffer */
                        ret = sendbytes(i2c_adap, pmsg);
                        if (ret >= 1)
                                bit_dbg(2, &i2c_adap->dev, "wrote %d byte%s\n",
                                        ret, ret == 1 ? "" : "s");
                        if (ret < pmsg->len) {
                                if (ret >= 0)
                                        ret = -EIO;
                                goto bailout;
                        }
                }
        }
        ret = i;

bailout:
        bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
        i2c_stop(adap);

        if (adap->post_xfer)
                adap->post_xfer(i2c_adap);
        return ret;
}

/*
 * We print a warning when we are not flagged to support atomic transfers but
 * will try anyhow. That's what the I2C core would do as well. Sadly, we can't
 * modify the algorithm struct at probe time because this struct is exported
 * 'const'.
 */
static int bit_xfer_atomic(struct i2c_adapter *i2c_adap, struct i2c_msg msgs[],
                           int num)
{
        struct i2c_algo_bit_data *adap = i2c_adap->algo_data;

        if (!adap->can_do_atomic)
                dev_warn(&i2c_adap->dev, "not flagged for atomic transfers\n");

        return bit_xfer(i2c_adap, msgs, num);
}

static u32 bit_func(struct i2c_adapter *adap)
{
        return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL |
               I2C_FUNC_SMBUS_READ_BLOCK_DATA |
               I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
               I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
}


/* -----exported algorithm data: -------------------------------------  */

const struct i2c_algorithm i2c_bit_algo = {
        .master_xfer = bit_xfer,
        .master_xfer_atomic = bit_xfer_atomic,
        .functionality = bit_func,
};
EXPORT_SYMBOL(i2c_bit_algo);

static const struct i2c_adapter_quirks i2c_bit_quirk_no_clk_stretch = {
        .flags = I2C_AQ_NO_CLK_STRETCH,
};

/*
 * registering functions to load algorithms at runtime
 */
static int __i2c_bit_add_bus(struct i2c_adapter *adap,
                             int (*add_adapter)(struct i2c_adapter *))
{
        struct i2c_algo_bit_data *bit_adap = adap->algo_data;
        int ret;

        if (bit_test) {
                ret = test_bus(adap);
                if (bit_test >= 2 && ret < 0)
                        return -ENODEV;
        }

        /* register new adapter to i2c module... */
        adap->algo = &i2c_bit_algo;
        adap->retries = 3;
        if (bit_adap->getscl == NULL)
                adap->quirks = &i2c_bit_quirk_no_clk_stretch;

        /*
         * We tried forcing SCL/SDA to an initial state here. But that caused a
         * regression, sadly. Check Bugzilla #200045 for details.
         */

        ret = add_adapter(adap);
        if (ret < 0)
                return ret;

        /* Complain if SCL can't be read */
        if (bit_adap->getscl == NULL) {
                dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
                dev_warn(&adap->dev, "Bus may be unreliable\n");
        }
        return 0;
}

int i2c_bit_add_bus(struct i2c_adapter *adap)
{
        return __i2c_bit_add_bus(adap, i2c_add_adapter);
}
EXPORT_SYMBOL(i2c_bit_add_bus);

int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
{
        return __i2c_bit_add_bus(adap, i2c_add_numbered_adapter);
}
EXPORT_SYMBOL(i2c_bit_add_numbered_bus);

MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
MODULE_DESCRIPTION("I2C-Bus bit-banging algorithm");
MODULE_LICENSE("GPL");