FreeBSD/Linux Kernel Cross Reference
sys/arm/freescale/imx/imx_i2c.c

     /*-
      * Copyright (C) 2008-2009 Semihalf, Michal Hajduk
      * Copyright (c) 2012, 2013 The FreeBSD Foundation
      * Copyright (c) 2015 Ian Lepore <ian@FreeBSD.org>
      * All rights reserved.
      *
      * Portions of this software were developed by Oleksandr Rybalko
      * under sponsorship from the FreeBSD Foundation.
      *
     * 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 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 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.
     */
    
    /*
     * I2C driver for Freescale i.MX hardware.
     *
     * Note that the hardware is capable of running as both a master and a slave.
     * This driver currently implements only master-mode operations.
     *
     * This driver supports multi-master i2c buses, by detecting bus arbitration
     * loss and returning IIC_EBUSBSY status.  Notably, it does not do any kind of
     * retries if some other master jumps onto the bus and interrupts one of our
     * transfer cycles resulting in arbitration loss in mid-transfer.  The caller
     * must handle retries in a way that makes sense for the slave being addressed.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bus.h>
    #include <sys/gpio.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/module.h>
    #include <sys/resource.h>
    #include <sys/sysctl.h>
    
    #include <machine/bus.h>
    #include <machine/resource.h>
    #include <sys/rman.h>
    
    #include <arm/freescale/imx/imx_ccmvar.h>
    
    #include <dev/iicbus/iiconf.h>
    #include <dev/iicbus/iicbus.h>
    #include <dev/iicbus/iic_recover_bus.h>
    #include "iicbus_if.h"
    
    #include <dev/ofw/openfirm.h>
    #include <dev/ofw/ofw_bus.h>
    #include <dev/ofw/ofw_bus_subr.h>
    
    #include <dev/fdt/fdt_pinctrl.h>
    #include <dev/gpio/gpiobusvar.h>
    
    #if defined(__aarch64__)
    #define IMX_ENABLE_CLOCKS
    #endif
    
    #ifdef IMX_ENABLE_CLOCKS
    #include <dev/extres/clk/clk.h>
    #endif
    
    #define I2C_ADDR_REG            0x00 /* I2C slave address register */
    #define I2C_FDR_REG             0x04 /* I2C frequency divider register */
    #define I2C_CONTROL_REG         0x08 /* I2C control register */
    #define I2C_STATUS_REG          0x0C /* I2C status register */
    #define I2C_DATA_REG            0x10 /* I2C data register */
    #define I2C_DFSRR_REG           0x14 /* I2C Digital Filter Sampling rate */
    
    #define I2CCR_MEN               (1 << 7) /* Module enable */
    #define I2CCR_MSTA              (1 << 5) /* Master/slave mode */
    #define I2CCR_MTX               (1 << 4) /* Transmit/receive mode */
    #define I2CCR_TXAK              (1 << 3) /* Transfer acknowledge */
    #define I2CCR_RSTA              (1 << 2) /* Repeated START */
    
    #define I2CSR_MCF               (1 << 7) /* Data transfer */
    #define I2CSR_MASS              (1 << 6) /* Addressed as a slave */
    #define I2CSR_MBB               (1 << 5) /* Bus busy */
   #define I2CSR_MAL               (1 << 4) /* Arbitration lost */
   #define I2CSR_SRW               (1 << 2) /* Slave read/write */
   #define I2CSR_MIF               (1 << 1) /* Module interrupt */
   #define I2CSR_RXAK              (1 << 0) /* Received acknowledge */
   
   #define I2C_BAUD_RATE_FAST      0x31
   #define I2C_BAUD_RATE_DEF       0x3F
   #define I2C_DFSSR_DIV           0x10
   
   /*
    * A table of available divisors and the associated coded values to put in the
    * FDR register to achieve that divisor.. There is no algorithmic relationship I
    * can see between divisors and the codes that go into the register.  The table
    * begins and ends with entries that handle insane configuration values.
    */
   struct clkdiv {
           u_int divisor;
           u_int regcode;
   };
   static struct clkdiv clkdiv_table[] = {
           {    0, 0x20 }, {   22, 0x20 }, {   24, 0x21 }, {   26, 0x22 }, 
           {   28, 0x23 }, {   30, 0x00 }, {   32, 0x24 }, {   36, 0x25 }, 
           {   40, 0x26 }, {   42, 0x03 }, {   44, 0x27 }, {   48, 0x28 }, 
           {   52, 0x05 }, {   56, 0x29 }, {   60, 0x06 }, {   64, 0x2a }, 
           {   72, 0x2b }, {   80, 0x2c }, {   88, 0x09 }, {   96, 0x2d }, 
           {  104, 0x0a }, {  112, 0x2e }, {  128, 0x2f }, {  144, 0x0c }, 
           {  160, 0x30 }, {  192, 0x31 }, {  224, 0x32 }, {  240, 0x0f }, 
           {  256, 0x33 }, {  288, 0x10 }, {  320, 0x34 }, {  384, 0x35 }, 
           {  448, 0x36 }, {  480, 0x13 }, {  512, 0x37 }, {  576, 0x14 }, 
           {  640, 0x38 }, {  768, 0x39 }, {  896, 0x3a }, {  960, 0x17 }, 
           { 1024, 0x3b }, { 1152, 0x18 }, { 1280, 0x3c }, { 1536, 0x3d }, 
           { 1792, 0x3e }, { 1920, 0x1b }, { 2048, 0x3f }, { 2304, 0x1c }, 
           { 2560, 0x1d }, { 3072, 0x1e }, { 3840, 0x1f }, {UINT_MAX, 0x1f} 
   };
   
   static struct ofw_compat_data compat_data[] = {
           {"fsl,imx21-i2c",  1},
           {"fsl,imx6q-i2c",  1},
           {"fsl,imx-i2c",    1},
           {NULL,             0}
   };
   
   struct i2c_softc {
           device_t                dev;
           device_t                iicbus;
           struct resource         *res;
           int                     rid;
           sbintime_t              byte_time_sbt;
           int                     rb_pinctl_idx;
           gpio_pin_t              rb_sclpin;
           gpio_pin_t              rb_sdapin;
           u_int                   debug;
           u_int                   slave;
   #ifdef IMX_ENABLE_CLOCKS
           clk_t                   ipgclk;
   #endif
   };
   
   #define DEVICE_DEBUGF(sc, lvl, fmt, args...) \
       if ((lvl) <= (sc)->debug) \
           device_printf((sc)->dev, fmt, ##args)
   
   #define DEBUGF(sc, lvl, fmt, args...) \
       if ((lvl) <= (sc)->debug) \
           printf(fmt, ##args)
   
   static phandle_t i2c_get_node(device_t, device_t);
   static int i2c_probe(device_t);
   static int i2c_attach(device_t);
   static int i2c_detach(device_t);
   
   static int i2c_repeated_start(device_t, u_char, int);
   static int i2c_start(device_t, u_char, int);
   static int i2c_stop(device_t);
   static int i2c_reset(device_t, u_char, u_char, u_char *);
   static int i2c_read(device_t, char *, int, int *, int, int);
   static int i2c_write(device_t, const char *, int, int *, int);
   
   static device_method_t i2c_methods[] = {
           DEVMETHOD(device_probe,                 i2c_probe),
           DEVMETHOD(device_attach,                i2c_attach),
           DEVMETHOD(device_detach,                i2c_detach),
   
           /* OFW methods */
           DEVMETHOD(ofw_bus_get_node,             i2c_get_node),
   
           DEVMETHOD(iicbus_callback,              iicbus_null_callback),
           DEVMETHOD(iicbus_repeated_start,        i2c_repeated_start),
           DEVMETHOD(iicbus_start,                 i2c_start),
           DEVMETHOD(iicbus_stop,                  i2c_stop),
           DEVMETHOD(iicbus_reset,                 i2c_reset),
           DEVMETHOD(iicbus_read,                  i2c_read),
           DEVMETHOD(iicbus_write,                 i2c_write),
           DEVMETHOD(iicbus_transfer,              iicbus_transfer_gen),
   
           DEVMETHOD_END
   };
   
   static driver_t i2c_driver = {
           "imx_i2c",
           i2c_methods,
           sizeof(struct i2c_softc),
   };
   
   DRIVER_MODULE(imx_i2c, simplebus, i2c_driver, 0, 0);
   DRIVER_MODULE(ofw_iicbus, imx_i2c, ofw_iicbus_driver, 0, 0);
   MODULE_DEPEND(imx_i2c, iicbus, 1, 1, 1);
   SIMPLEBUS_PNP_INFO(compat_data);
   
   static phandle_t
   i2c_get_node(device_t bus, device_t dev)
   {
           /*
            * Share controller node with iicbus device
            */
           return ofw_bus_get_node(bus);
   }
   
   static __inline void
   i2c_write_reg(struct i2c_softc *sc, bus_size_t off, uint8_t val)
   {
   
           bus_write_1(sc->res, off, val);
   }
   
   static __inline uint8_t
   i2c_read_reg(struct i2c_softc *sc, bus_size_t off)
   {
   
           return (bus_read_1(sc->res, off));
   }
   
   static __inline void
   i2c_flag_set(struct i2c_softc *sc, bus_size_t off, uint8_t mask)
   {
           uint8_t status;
   
           status = i2c_read_reg(sc, off);
           status |= mask;
           i2c_write_reg(sc, off, status);
   }
   
   /* Wait for bus to become busy or not-busy. */
   static int
   wait_for_busbusy(struct i2c_softc *sc, int wantbusy)
   {
           int retry, srb;
   
           retry = 1000;
           while (retry --) {
                   srb = i2c_read_reg(sc, I2C_STATUS_REG) & I2CSR_MBB;
                   if ((srb && wantbusy) || (!srb && !wantbusy))
                           return (IIC_NOERR);
                   DELAY(1);
           }
           return (IIC_ETIMEOUT);
   }
   
   /* Wait for transfer to complete, optionally check RXAK. */
   static int
   wait_for_xfer(struct i2c_softc *sc, int checkack)
   {
           int retry, sr;
   
           /*
            * Sleep for about the time it takes to transfer a byte (with precision
            * set to tolerate 5% oversleep).  We calculate the approximate byte
            * transfer time when we set the bus speed divisor.  Slaves are allowed
            * to do clock-stretching so the actual transfer time can be larger, but
            * this gets the bulk of the waiting out of the way without tying up the
            * processor the whole time.
            */
           pause_sbt("imxi2c", sc->byte_time_sbt, sc->byte_time_sbt / 20, 0);
   
           retry = 10000;
           while (retry --) {
                   sr = i2c_read_reg(sc, I2C_STATUS_REG);
                   if (sr & I2CSR_MIF) {
                           if (sr & I2CSR_MAL) 
                                   return (IIC_EBUSERR);
                           else if (checkack && (sr & I2CSR_RXAK))
                                   return (IIC_ENOACK);
                           else
                                   return (IIC_NOERR);
                   }
                   DELAY(1);
           }
           return (IIC_ETIMEOUT);
   }
   
   /*
    * Implement the error handling shown in the state diagram of the imx6 reference
    * manual.  If there was an error, then:
    *  - Clear master mode (MSTA and MTX).
    *  - Wait for the bus to become free or for a timeout to happen.
    *  - Disable the controller.
    */
   static int
   i2c_error_handler(struct i2c_softc *sc, int error)
   {
   
           if (error != 0) {
                   i2c_write_reg(sc, I2C_STATUS_REG, 0);
                   i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN);
                   wait_for_busbusy(sc, false);
                   i2c_write_reg(sc, I2C_CONTROL_REG, 0);
           }
           return (error);
   }
   
   static int
   i2c_recover_getsda(void *ctx)
   {
           bool active;
   
           gpio_pin_is_active(((struct i2c_softc *)ctx)->rb_sdapin, &active);
           return (active);
   }
   
   static void
   i2c_recover_setsda(void *ctx, int value)
   {
   
           gpio_pin_set_active(((struct i2c_softc *)ctx)->rb_sdapin, value);
   }
   
   static int
   i2c_recover_getscl(void *ctx)
   {
           bool active;
   
           gpio_pin_is_active(((struct i2c_softc *)ctx)->rb_sclpin, &active);
           return (active);
   
   }
   
   static void
   i2c_recover_setscl(void *ctx, int value)
   {
   
           gpio_pin_set_active(((struct i2c_softc *)ctx)->rb_sclpin, value);
   }
   
   static int
   i2c_recover_bus(struct i2c_softc *sc)
   {
           struct iicrb_pin_access pins;
           int err;
   
           /*
            * If we have gpio pinmux config, reconfigure the pins to gpio mode,
            * invoke iic_recover_bus which checks for a hung bus and bitbangs a
            * recovery sequence if necessary, then configure the pins back to i2c
            * mode (idx 0).
            */
           if (sc->rb_pinctl_idx == 0)
                   return (0);
   
           fdt_pinctrl_configure(sc->dev, sc->rb_pinctl_idx);
   
           pins.ctx = sc;
           pins.getsda = i2c_recover_getsda;
           pins.setsda = i2c_recover_setsda;
           pins.getscl = i2c_recover_getscl;
           pins.setscl = i2c_recover_setscl;
           err = iic_recover_bus(&pins);
   
           fdt_pinctrl_configure(sc->dev, 0);
   
           return (err);
   }
   
   static int
   i2c_probe(device_t dev)
   {
   
           if (!ofw_bus_status_okay(dev))
                   return (ENXIO);
   
           if (ofw_bus_search_compatible(dev, compat_data)->ocd_data == 0)
                   return (ENXIO);
   
           device_set_desc(dev, "Freescale i.MX I2C");
   
           return (BUS_PROBE_DEFAULT);
   }
   
   static int
   i2c_attach(device_t dev)
   {
           char wrkstr[16];
           struct i2c_softc *sc;
           phandle_t node;
           int err, cfgidx;
   
           sc = device_get_softc(dev);
           sc->dev = dev;
           sc->rid = 0;
   
   #ifdef IMX_ENABLE_CLOCKS
           if (clk_get_by_ofw_index(sc->dev, 0, 0, &sc->ipgclk) != 0) {
                   device_printf(dev, "could not get ipg clock");
                   return (ENOENT);
           }
   
           err = clk_enable(sc->ipgclk);
           if (err != 0) {
                   device_printf(sc->dev, "could not enable ipg clock\n");
                   return (err);
           }
   #endif
   
           sc->res = bus_alloc_resource_any(dev, SYS_RES_MEMORY, &sc->rid,
               RF_ACTIVE);
           if (sc->res == NULL) {
                   device_printf(dev, "could not allocate resources");
                   return (ENXIO);
           }
   
           sc->iicbus = device_add_child(dev, "iicbus", -1);
           if (sc->iicbus == NULL) {
                   device_printf(dev, "could not add iicbus child");
                   return (ENXIO);
           }
   
           /* Set up debug-enable sysctl. */
           SYSCTL_ADD_INT(device_get_sysctl_ctx(sc->dev), 
               SYSCTL_CHILDREN(device_get_sysctl_tree(sc->dev)),
               OID_AUTO, "debug", CTLFLAG_RWTUN, &sc->debug, 0,
               "Enable debug; 1=reads/writes, 2=add starts/stops");
   
           /*
            * Set up for bus recovery using gpio pins, if the pinctrl and gpio
            * properties are present.  This is optional.  If all the config data is
            * not in place, we just don't do gpio bitbang bus recovery.
            */
           node = ofw_bus_get_node(sc->dev);
   
           err = gpio_pin_get_by_ofw_property(dev, node, "scl-gpios",
               &sc->rb_sclpin);
           if (err != 0)
                   goto no_recovery;
           err = gpio_pin_get_by_ofw_property(dev, node, "sda-gpios",
               &sc->rb_sdapin);
           if (err != 0)
                   goto no_recovery;
   
           /*
            * Preset the gpio pins to output high (idle bus state).  The signal
            * won't actually appear on the pins until the bus recovery code changes
            * the pinmux config from i2c to gpio.
            */
           gpio_pin_setflags(sc->rb_sclpin, GPIO_PIN_OUTPUT);
           gpio_pin_setflags(sc->rb_sdapin, GPIO_PIN_OUTPUT);
           gpio_pin_set_active(sc->rb_sclpin, true);
           gpio_pin_set_active(sc->rb_sdapin, true);
   
           /*
            * Obtain the index of pinctrl node for bus recovery using gpio pins,
            * then confirm that pinctrl properties exist for that index and for the
            * default pinctrl-0.  If sc->rb_pinctl_idx is non-zero, the reset code
            * will also do a bus recovery, so setting this value must be last.
            */
           err = ofw_bus_find_string_index(node, "pinctrl-names", "gpio", &cfgidx);
           if (err == 0) {
                   snprintf(wrkstr, sizeof(wrkstr), "pinctrl-%d", cfgidx);
                   if (OF_hasprop(node, "pinctrl-0") && OF_hasprop(node, wrkstr))
                           sc->rb_pinctl_idx = cfgidx;
           }
   
   no_recovery:
   
           /* We don't do a hardware reset here because iicbus_attach() does it. */
   
           /* Probe and attach the iicbus when interrupts are available. */
           return (bus_delayed_attach_children(dev));
   }
   
   static int
   i2c_detach(device_t dev)
   {
           struct i2c_softc *sc;
           int error;
   
           sc = device_get_softc(dev);
   
   #ifdef IMX_ENABLE_CLOCKS
           error = clk_disable(sc->ipgclk);
           if (error != 0) {
                   device_printf(sc->dev, "could not disable ipg clock\n");
                   return (error);
           }
   #endif
   
           if ((error = bus_generic_detach(sc->dev)) != 0) {
                   device_printf(sc->dev, "cannot detach child devices\n");
                   return (error);
           }
   
           if (sc->iicbus != NULL)
                   device_delete_child(dev, sc->iicbus);
   
           /* Release bus-recover pins; gpio_pin_release() handles NULL args. */
           gpio_pin_release(sc->rb_sclpin);
           gpio_pin_release(sc->rb_sdapin);
   
           if (sc->res != NULL)
                   bus_release_resource(dev, SYS_RES_MEMORY, 0, sc->res);
   
           return (0);
   }
   
   static int
   i2c_repeated_start(device_t dev, u_char slave, int timeout)
   {
           struct i2c_softc *sc;
           int error;
   
           sc = device_get_softc(dev);
   
           if ((i2c_read_reg(sc, I2C_STATUS_REG) & I2CSR_MBB) == 0) {
                   return (IIC_EBUSERR);
           }
   
           /*
            * Set repeated start condition, delay (per reference manual, min 156nS)
            * before writing slave address, wait for ack after write.
            */
           i2c_flag_set(sc, I2C_CONTROL_REG, I2CCR_RSTA);
           DELAY(1);
           i2c_write_reg(sc, I2C_STATUS_REG, 0x0);
           i2c_write_reg(sc, I2C_DATA_REG, slave);
           sc->slave = slave;
           DEVICE_DEBUGF(sc, 2, "rstart 0x%02x\n", sc->slave);
           error = wait_for_xfer(sc, true);
           return (i2c_error_handler(sc, error));
   }
   
   static int
   i2c_start_ll(device_t dev, u_char slave, int timeout)
   {
           struct i2c_softc *sc;
           int error;
   
           sc = device_get_softc(dev);
   
           i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN);
           DELAY(10); /* Delay for controller to sample bus state. */
           if (i2c_read_reg(sc, I2C_STATUS_REG) & I2CSR_MBB) {
                   return (i2c_error_handler(sc, IIC_EBUSERR));
           }
           i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN | I2CCR_MSTA | I2CCR_MTX);
           if ((error = wait_for_busbusy(sc, true)) != IIC_NOERR)
                   return (i2c_error_handler(sc, error));
           i2c_write_reg(sc, I2C_STATUS_REG, 0);
           i2c_write_reg(sc, I2C_DATA_REG, slave);
           sc->slave = slave;
           DEVICE_DEBUGF(sc, 2, "start  0x%02x\n", sc->slave);
           error = wait_for_xfer(sc, true);
           return (i2c_error_handler(sc, error));
   }
   
   static int
   i2c_start(device_t dev, u_char slave, int timeout)
   {
           struct i2c_softc *sc;
           int error;
   
           sc = device_get_softc(dev);
   
           /*
            * Invoke the low-level code to put the bus into master mode and address
            * the given slave.  If that fails, idle the controller and attempt a
            * bus recovery, and then try again one time.  Signaling a start and
            * addressing the slave is the only operation that a low-level driver
            * can safely retry without any help from the upper layers that know
            * more about the slave device.
            */
           if ((error = i2c_start_ll(dev, slave, timeout)) != 0) {
                   i2c_write_reg(sc, I2C_CONTROL_REG, 0x0);
                   if ((error = i2c_recover_bus(sc)) != 0)
                           return (error);
                   error = i2c_start_ll(dev, slave, timeout);
           }
           return (error);
   }
   
   static int
   i2c_stop(device_t dev)
   {
           struct i2c_softc *sc;
   
           sc = device_get_softc(dev);
   
           i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN);
           wait_for_busbusy(sc, false);
           i2c_write_reg(sc, I2C_CONTROL_REG, 0);
           DEVICE_DEBUGF(sc, 2, "stop   0x%02x\n", sc->slave);
           return (IIC_NOERR);
   }
   
   static int
   i2c_reset(device_t dev, u_char speed, u_char addr, u_char *oldadr)
   {
           struct i2c_softc *sc;
           u_int busfreq, div, i, ipgfreq;
   #ifdef IMX_ENABLE_CLOCKS
           int err;
           uint64_t freq;
   #endif
   
           sc = device_get_softc(dev);
   
           DEVICE_DEBUGF(sc, 1, "reset\n");
   
           /*
            * Look up the divisor that gives the nearest speed that doesn't exceed
            * the configured value for the bus.
            */
   #ifdef IMX_ENABLE_CLOCKS
           err = clk_get_freq(sc->ipgclk, &freq);
           if (err != 0) {
                   device_printf(sc->dev, "cannot get frequency\n");
                   return (err);
           }
           ipgfreq = (int32_t)freq;
   #else
           ipgfreq = imx_ccm_ipg_hz();
   #endif
           busfreq = IICBUS_GET_FREQUENCY(sc->iicbus, speed);
           div = howmany(ipgfreq, busfreq);
           for (i = 0; i < nitems(clkdiv_table); i++) {
                   if (clkdiv_table[i].divisor >= div)
                           break;
           }
   
           /*
            * Calculate roughly how long it will take to transfer a byte (which
            * requires 9 clock cycles) at the new bus speed.  This value is used to
            * pause() while waiting for transfer-complete.  With a 66MHz IPG clock
            * and the actual i2c bus speeds that leads to, for nominal 100KHz and
            * 400KHz bus speeds the transfer times are roughly 104uS and 22uS.
            */
           busfreq = ipgfreq / clkdiv_table[i].divisor;
           sc->byte_time_sbt = SBT_1US * (9000000 / busfreq);
   
           /*
            * Disable the controller (do the reset), and set the new clock divisor.
            */
           i2c_write_reg(sc, I2C_STATUS_REG, 0x0);
           i2c_write_reg(sc, I2C_CONTROL_REG, 0x0);
           i2c_write_reg(sc, I2C_FDR_REG, (uint8_t)clkdiv_table[i].regcode);
   
           /*
            * Now that the controller is idle, perform bus recovery.  If the bus
            * isn't hung, this a fairly fast no-op.
            */
           return (i2c_recover_bus(sc));
   }
   
   static int
   i2c_read(device_t dev, char *buf, int len, int *read, int last, int delay)
   {
           struct i2c_softc *sc;
           int error, reg;
   
           sc = device_get_softc(dev);
           *read = 0;
   
           DEVICE_DEBUGF(sc, 1, "read   0x%02x len %d: ", sc->slave, len);
           if (len) {
                   if (len == 1)
                           i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN |
                               I2CCR_MSTA | I2CCR_TXAK);
                   else
                           i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN |
                               I2CCR_MSTA);
                   /* Dummy read to prime the receiver. */
                   i2c_write_reg(sc, I2C_STATUS_REG, 0x0);
                   i2c_read_reg(sc, I2C_DATA_REG);
           }
   
           error = 0;
           *read = 0;
           while (*read < len) {
                   if ((error = wait_for_xfer(sc, false)) != IIC_NOERR)
                           break;
                   i2c_write_reg(sc, I2C_STATUS_REG, 0x0);
                   if (last) {
                           if (*read == len - 2) {
                                   /* NO ACK on last byte */
                                   i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN |
                                       I2CCR_MSTA | I2CCR_TXAK);
                           } else if (*read == len - 1) {
                                   /* Transfer done, signal stop. */
                                   i2c_write_reg(sc, I2C_CONTROL_REG, I2CCR_MEN |
                                       I2CCR_TXAK);
                                   wait_for_busbusy(sc, false);
                           }
                   }
                   reg = i2c_read_reg(sc, I2C_DATA_REG);
                   DEBUGF(sc, 1, "0x%02x ", reg);
                   *buf++ = reg;
                   (*read)++;
           }
           DEBUGF(sc, 1, "\n");
   
           return (i2c_error_handler(sc, error));
   }
   
   static int
   i2c_write(device_t dev, const char *buf, int len, int *sent, int timeout)
   {
           struct i2c_softc *sc;
           int error;
   
           sc = device_get_softc(dev);
   
           error = 0;
           *sent = 0;
           DEVICE_DEBUGF(sc, 1, "write  0x%02x len %d: ", sc->slave, len);
           while (*sent < len) {
                   DEBUGF(sc, 1, "0x%02x ", *buf);
                   i2c_write_reg(sc, I2C_STATUS_REG, 0x0);
                   i2c_write_reg(sc, I2C_DATA_REG, *buf++);
                   if ((error = wait_for_xfer(sc, true)) != IIC_NOERR)
                           break;
                   (*sent)++;
           }
           DEBUGF(sc, 1, "\n");
           return (i2c_error_handler(sc, error));
   }

Cache object: 334d05a3bf7ee2fe42c4f37f21772bb6