iicbb.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 1998, 2001 Nicolas Souchu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
/*
 * Generic I2C bit-banging code
 *
 * Example:
 *
 *      iicbus
 *       /  \ 
 *    iicbb pcf
 *     |  \
 *   bti2c lpbb
 *
 * From Linux I2C generic interface
 * (c) 1998 Gerd Knorr <kraxel@cs.tu-berlin.de>
 *
 */
 
#include "opt_platform.h"
 
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/module.h>
#include <sys/bus.h>
#include <sys/sysctl.h>
#include <sys/uio.h>
 
#ifdef FDT
#include <dev/ofw/ofw_bus.h>
#include <dev/ofw/ofw_bus_subr.h>
#include <dev/fdt/fdt_common.h>
#endif
 
#include <dev/iicbus/iiconf.h>
#include <dev/iicbus/iicbus.h>
 
#include <dev/smbus/smbconf.h>
 
#include "iicbus_if.h"
#include "iicbb_if.h"
 
/* Based on the SMBus specification. */
#define DEFAULT_SCL_LOW_TIMEOUT (25 * 1000)
 
struct iicbb_softc {
        device_t iicbus;
        u_int udelay;           /* signal toggle delay in usec */
        u_int io_latency;       /* approximate pin toggling latency */
        u_int scl_low_timeout;
};
 
static int iicbb_attach(device_t);
static void iicbb_child_detached(device_t, device_t);
static int iicbb_detach(device_t);
static int iicbb_print_child(device_t, device_t);
static int iicbb_probe(device_t);
 
static int iicbb_callback(device_t, int, caddr_t);
static int iicbb_start(device_t, u_char, int);
static int iicbb_repstart(device_t, u_char, int);
static int iicbb_stop(device_t);
static int iicbb_write(device_t, const char *, int, int *, int);
static int iicbb_read(device_t, char *, int, int *, int, int);
static int iicbb_reset(device_t, u_char, u_char, u_char *);
static int iicbb_transfer(device_t dev, struct iic_msg *msgs, uint32_t nmsgs);
static void iicbb_set_speed(struct iicbb_softc *sc, u_char);
#ifdef FDT
static phandle_t iicbb_get_node(device_t, device_t);
#endif
 
static device_method_t iicbb_methods[] = {
        /* device interface */
        DEVMETHOD(device_probe,         iicbb_probe),
        DEVMETHOD(device_attach,        iicbb_attach),
        DEVMETHOD(device_detach,        iicbb_detach),
 
        /* bus interface */
        DEVMETHOD(bus_child_detached,   iicbb_child_detached),
        DEVMETHOD(bus_print_child,      iicbb_print_child),
 
        /* iicbus interface */
        DEVMETHOD(iicbus_callback,      iicbb_callback),
        DEVMETHOD(iicbus_start,         iicbb_start),
        DEVMETHOD(iicbus_repeated_start, iicbb_repstart),
        DEVMETHOD(iicbus_stop,          iicbb_stop),
        DEVMETHOD(iicbus_write,         iicbb_write),
        DEVMETHOD(iicbus_read,          iicbb_read),
        DEVMETHOD(iicbus_reset,         iicbb_reset),
        DEVMETHOD(iicbus_transfer,      iicbb_transfer),
 
#ifdef FDT
        /* ofw_bus interface */
        DEVMETHOD(ofw_bus_get_node,     iicbb_get_node),
#endif
 
        { 0, 0 }
};
 
driver_t iicbb_driver = {
        "iicbb",
        iicbb_methods,
        sizeof(struct iicbb_softc),
};
 
devclass_t iicbb_devclass;
 
static int
iicbb_probe(device_t dev)
{
        device_set_desc(dev, "I2C bit-banging driver");
 
        return (0);
}
 
static int
iicbb_attach(device_t dev)
{
        struct iicbb_softc *sc = (struct iicbb_softc *)device_get_softc(dev);
 
        sc->iicbus = device_add_child(dev, "iicbus", -1);
        if (!sc->iicbus)
                return (ENXIO);
 
        sc->scl_low_timeout = DEFAULT_SCL_LOW_TIMEOUT;
 
        SYSCTL_ADD_UINT(device_get_sysctl_ctx(dev),
            SYSCTL_CHILDREN(device_get_sysctl_tree(dev)), OID_AUTO,
            "delay", CTLFLAG_RD, &sc->udelay,
            0, "Signal change delay controlled by bus frequency, microseconds");
 
        SYSCTL_ADD_UINT(device_get_sysctl_ctx(dev),
            SYSCTL_CHILDREN(device_get_sysctl_tree(dev)), OID_AUTO,
            "scl_low_timeout", CTLFLAG_RWTUN, &sc->scl_low_timeout,
            0, "SCL low timeout, microseconds");
        SYSCTL_ADD_UINT(device_get_sysctl_ctx(dev),
            SYSCTL_CHILDREN(device_get_sysctl_tree(dev)), OID_AUTO,
            "io_latency", CTLFLAG_RWTUN, &sc->io_latency,
            0, "Estimate of pin toggling latency, microseconds");
 
        bus_generic_attach(dev);
        return (0);
}
 
static int
iicbb_detach(device_t dev)
{
 
        bus_generic_detach(dev);
        device_delete_children(dev);
 
        return (0);
}
 
#ifdef FDT
static phandle_t
iicbb_get_node(device_t bus, device_t dev)
{
 
        /* We only have one child, the I2C bus, which needs our own node. */
        return (ofw_bus_get_node(bus));
}
#endif
 
static void
iicbb_child_detached( device_t dev, device_t child )
{
        struct iicbb_softc *sc = (struct iicbb_softc *)device_get_softc(dev);
 
        if (child == sc->iicbus)
                sc->iicbus = NULL;
}
 
static int
iicbb_print_child(device_t bus, device_t dev)
{
        int error;
        int retval = 0;
        u_char oldaddr;
 
        retval += bus_print_child_header(bus, dev);
        /* retrieve the interface I2C address */
        error = IICBB_RESET(device_get_parent(bus), IIC_FASTEST, 0, &oldaddr);
        if (error == IIC_ENOADDR) {
                retval += printf(" on %s master-only\n",
                                 device_get_nameunit(bus));
        } else {
                /* restore the address */
                IICBB_RESET(device_get_parent(bus), IIC_FASTEST, oldaddr, NULL);
 
                retval += printf(" on %s addr 0x%x\n",
                                 device_get_nameunit(bus), oldaddr & 0xff);
        }
 
        return (retval);
}
 
#define IICBB_DEBUG
#ifdef IICBB_DEBUG
static int i2c_debug = 0;
 
SYSCTL_DECL(_hw_i2c);
SYSCTL_INT(_hw_i2c, OID_AUTO, iicbb_debug, CTLFLAG_RWTUN,
    &i2c_debug, 0, "Enable i2c bit-banging driver debug");
 
#define I2C_DEBUG(x)    do {            \
                if (i2c_debug) (x);     \
        } while (0)
#else
#define I2C_DEBUG(x)
#endif
 
#define I2C_GETSDA(dev)         (IICBB_GETSDA(device_get_parent(dev)))
#define I2C_SETSDA(dev, x)      (IICBB_SETSDA(device_get_parent(dev), x))
#define I2C_GETSCL(dev)         (IICBB_GETSCL(device_get_parent(dev)))
#define I2C_SETSCL(dev, x)      (IICBB_SETSCL(device_get_parent(dev), x))
 
static int
iicbb_waitforscl(device_t dev)
{
        struct iicbb_softc *sc = device_get_softc(dev);
        sbintime_t fast_timeout;
        sbintime_t now, timeout;
 
        /* Spin for up to 1 ms, then switch to pause. */
        now = sbinuptime();
        fast_timeout = now + SBT_1MS;
        timeout = now + sc->scl_low_timeout * SBT_1US;
        do {
                if (I2C_GETSCL(dev))
                        return (0);
                now = sbinuptime();
        } while (now < fast_timeout);
        do {
                I2C_DEBUG(printf("."));
                pause_sbt("iicbb-scl-low", SBT_1MS, C_PREL(8), 0);
                if (I2C_GETSCL(dev))
                        return (0);
                now = sbinuptime();
        } while (now < timeout);
 
        I2C_DEBUG(printf("*"));
        return (IIC_ETIMEOUT);
}
 
/* Start the high phase of the clock. */
static int
iicbb_clockin(device_t dev, int sda)
{
 
        /*
         * Precondition: SCL is low.
         * Action:
         * - set SDA to the value;
         * - release SCL and wait until it's high.
         * The caller is responsible for keeping SCL high for udelay.
         *
         * There should be a data set-up time, 250 ns minimum, between setting
         * SDA and raising SCL.  It's expected that the I/O access latency will
         * naturally provide that delay.
         */
        I2C_SETSDA(dev, sda);
        I2C_SETSCL(dev, 1);
        return (iicbb_waitforscl(dev));
}
 
/*
 * End the high phase of the clock and wait out the low phase
 * as nothing interesting happens during it anyway.
 */
static void
iicbb_clockout(device_t dev)
{
        struct iicbb_softc *sc = device_get_softc(dev);
 
        /*
         * Precondition: SCL is high.
         * Action:
         * - pull SCL low and hold for udelay.
         */
        I2C_SETSCL(dev, 0);
        DELAY(sc->udelay);
}
 
static int
iicbb_sendbit(device_t dev, int bit)
{
        struct iicbb_softc *sc = device_get_softc(dev);
        int err;
 
        err = iicbb_clockin(dev, bit);
        if (err != 0)
                return (err);
        DELAY(sc->udelay);
        iicbb_clockout(dev);
        return (0);
}
 
/*
 * Waiting for ACKNOWLEDGE.
 *
 * When a chip is being addressed or has received data it will issue an
 * ACKNOWLEDGE pulse. Therefore the MASTER must release the DATA line
 * (set it to high level) and then release the CLOCK line.
 * Now it must wait for the SLAVE to pull the DATA line low.
 * Actually on the bus this looks like a START condition so nothing happens
 * because of the fact that the IC's that have not been addressed are doing
 * nothing.
 *
 * When the SLAVE has pulled this line low the MASTER will take the CLOCK
 * line low and then the SLAVE will release the SDA (data) line.
 */
static int
iicbb_getack(device_t dev)
{
        struct iicbb_softc *sc = device_get_softc(dev);
        int noack, err;
        int t;
 
        /* Release SDA so that the slave can drive it. */
        err = iicbb_clockin(dev, 1);
        if (err != 0) {
                I2C_DEBUG(printf("! "));
                return (err);
        }
 
        /* Sample SDA until ACK (low) or udelay runs out. */
        for (t = 0; t < sc->udelay; t++) {
                noack = I2C_GETSDA(dev);
                if (!noack)
                        break;
                DELAY(1);
        }
 
        DELAY(sc->udelay - t);
        iicbb_clockout(dev);
 
        I2C_DEBUG(printf("%c ", noack ? '-' : '+'));
        return (noack ? IIC_ENOACK : 0);
}
 
static int
iicbb_sendbyte(device_t dev, uint8_t data)
{
        int err, i;
 
        for (i = 7; i >= 0; i--) {
                err = iicbb_sendbit(dev, (data & (1 << i)) != 0);
                if (err != 0) {
                        I2C_DEBUG(printf("w!"));
                        return (err);
                }
        }
        I2C_DEBUG(printf("w%02x", data));
        return (0);
}
 
static int
iicbb_readbyte(device_t dev, bool last, uint8_t *data)
{
        struct iicbb_softc *sc = device_get_softc(dev);
        int i, err;
 
        /*
         * Release SDA so that the slave can drive it.
         * We do not use iicbb_clockin() here because we need to release SDA
         * only once and then we just pulse the SCL.
         */
        *data = 0;
        I2C_SETSDA(dev, 1);
        for (i = 7; i >= 0; i--) {
                I2C_SETSCL(dev, 1);
                err = iicbb_waitforscl(dev);
                if (err != 0) {
                        I2C_DEBUG(printf("r! "));
                        return (err);
                }
                DELAY((sc->udelay + 1) / 2);
                if (I2C_GETSDA(dev))
                        *data |= 1 << i;
                DELAY((sc->udelay + 1) / 2);
                iicbb_clockout(dev);
        }
 
        /*
         * Send master->slave ACK (low) for more data,
         * NoACK (high) otherwise.
         */
        iicbb_sendbit(dev, last);
        I2C_DEBUG(printf("r%02x%c ", *data, last ? '-' : '+'));
        return (0);
}
 
static int
iicbb_callback(device_t dev, int index, caddr_t data)
{
        return (IICBB_CALLBACK(device_get_parent(dev), index, data));
}
 
static int
iicbb_reset(device_t dev, u_char speed, u_char addr, u_char *oldaddr)
{
        iicbb_set_speed(device_get_softc(dev), speed);
        return (IICBB_RESET(device_get_parent(dev), speed, addr, oldaddr));
}
 
static int
iicbb_start_impl(device_t dev, u_char slave, bool repstart)
{
        struct iicbb_softc *sc = device_get_softc(dev);
        int error;
 
        if (!repstart) {
                I2C_DEBUG(printf("<<"));
 
                /* SCL must be high on the idle bus. */
                if (iicbb_waitforscl(dev) != 0) {
                        I2C_DEBUG(printf("C!\n"));
                        return (IIC_EBUSERR);
                }
        } else {
                I2C_DEBUG(printf("<"));
                error = iicbb_clockin(dev, 1);
                if (error != 0)
                        return (error);
 
                /* SDA will go low in the middle of the SCL high phase. */
                DELAY((sc->udelay + 1) / 2);
        }
 
        /*
         * SDA must be high after the earlier stop condition or the end
         * of Ack/NoAck pulse.
         */
        if (!I2C_GETSDA(dev)) {
                I2C_DEBUG(printf("D!\n"));
                return (IIC_EBUSERR);
        }
 
        /* Start: SDA high->low. */
        I2C_SETSDA(dev, 0);
 
        /* Wait the second half of the SCL high phase. */
        DELAY((sc->udelay + 1) / 2);
 
        /* Pull SCL low to keep the bus reserved. */
        iicbb_clockout(dev);
 
        /* send address */
        error = iicbb_sendbyte(dev, slave);
 
        /* check for ack */
        if (error == 0)
                error = iicbb_getack(dev);
        if (error != 0)
                (void)iicbb_stop(dev);
        return (error);
}
 
/* NB: the timeout is ignored. */
static int
iicbb_start(device_t dev, u_char slave, int timeout)
{
        return (iicbb_start_impl(dev, slave, false));
}
 
/* NB: the timeout is ignored. */
static int
iicbb_repstart(device_t dev, u_char slave, int timeout)
{
        return (iicbb_start_impl(dev, slave, true));
}
 
static int
iicbb_stop(device_t dev)
{
        struct iicbb_softc *sc = device_get_softc(dev);
        int err = 0;
 
        /*
         * Stop: SDA goes from low to high in the middle of the SCL high phase.
         */
        err = iicbb_clockin(dev, 0);
        if (err != 0)
                return (err);
        DELAY((sc->udelay + 1) / 2);
        I2C_SETSDA(dev, 1);
        DELAY((sc->udelay + 1) / 2);
 
        I2C_DEBUG(printf("%s>>", err != 0 ? "!" : ""));
        I2C_DEBUG(printf("\n"));
        return (err);
}
 
/* NB: the timeout is ignored. */
static int
iicbb_write(device_t dev, const char *buf, int len, int *sent, int timeout)
{
        int bytes, error = 0;
 
        bytes = 0;
        while (len > 0) {
                /* send byte */
                iicbb_sendbyte(dev, (uint8_t)*buf++);
 
                /* check for ack */
                error = iicbb_getack(dev);
                if (error != 0)
                        break;
                bytes++;
                len--;
        }
 
        *sent = bytes;
        return (error);
}
 
/* NB: whatever delay is, it's ignored. */
static int
iicbb_read(device_t dev, char *buf, int len, int *read, int last, int delay)
{
        int bytes = 0;
        int err = 0;
 
        while (len > 0) {
                err = iicbb_readbyte(dev, (len == 1) ? last : 0,
                    (uint8_t *)buf);
                if (err != 0)
                        break;
                buf++;
                bytes++;
                len--;
        }
 
        *read = bytes;
        return (err);
}
 
static int
iicbb_transfer(device_t dev, struct iic_msg *msgs, uint32_t nmsgs)
{
        int error;
 
        error = IICBB_PRE_XFER(device_get_parent(dev));
        if (error)
                return (error);
 
        error = iicbus_transfer_gen(dev, msgs, nmsgs);
 
        IICBB_POST_XFER(device_get_parent(dev));
        return (error);
}
 
static void
iicbb_set_speed(struct iicbb_softc *sc, u_char speed)
{
        u_int busfreq;
        int period;
 
        /*
         * udelay is half a period, the clock is held high or low for this long.
         */
        busfreq = IICBUS_GET_FREQUENCY(sc->iicbus, speed);
        period = 1000000 / 2 / busfreq; /* Hz -> uS */
        period -= sc->io_latency;
        sc->udelay = MAX(period, 1);
}
 
DRIVER_MODULE(iicbus, iicbb, iicbus_driver, iicbus_devclass, 0, 0);
 
MODULE_DEPEND(iicbb, iicbus, IICBUS_MINVER, IICBUS_PREFVER, IICBUS_MAXVER);
MODULE_VERSION(iicbb, IICBB_MODVER);