i2c-mux.c

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/*
 * Multiplexed I2C bus driver.
 *
 * Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
 * Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
 * Copyright (c) 2009-2010 NSN GmbH & Co KG <[email protected]>
 *
 * Simplifies access to complex multiplexed I2C bus topologies, by presenting
 * each multiplexed bus segment as an additional I2C adapter.
 * Supports multi-level mux'ing (mux behind a mux).
 *
 * Based on:
 *  i2c-virt.c from Kumar Gala <[email protected]>
 *  i2c-virtual.c from Ken Harrenstien, Copyright (c) 2004 Google, Inc.
 *  i2c-virtual.c from Brian Kuschak <[email protected]>
 *
 * This file is licensed under the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>
#include <linux/of.h>
#include <linux/of_i2c.h>

/* multiplexer per channel data */
struct i2c_mux_priv {
    struct i2c_adapter adap;
    struct i2c_algorithm algo;

    struct i2c_adapter *parent;
    void *mux_priv; /* the mux chip/device */
    u32  chan_id;   /* the channel id */

    int (*select)(struct i2c_adapter *, void *mux_priv, u32 chan_id);
    int (*deselect)(struct i2c_adapter *, void *mux_priv, u32 chan_id);
};

static int i2c_mux_master_xfer(struct i2c_adapter *adap,
                   struct i2c_msg msgs[], int num)
{
    struct i2c_mux_priv *priv = adap->algo_data;
    struct i2c_adapter *parent = priv->parent;
    int ret;

    /* Switch to the right mux port and perform the transfer. */

    ret = priv->select(parent, priv->mux_priv, priv->chan_id);
    if (ret >= 0)
        ret = parent->algo->master_xfer(parent, msgs, num);
    if (priv->deselect)
        priv->deselect(parent, priv->mux_priv, priv->chan_id);

    return ret;
}

static int i2c_mux_smbus_xfer(struct i2c_adapter *adap,
                  u16 addr, unsigned short flags,
                  char read_write, u8 command,
                  int size, union i2c_smbus_data *data)
{
    struct i2c_mux_priv *priv = adap->algo_data;
    struct i2c_adapter *parent = priv->parent;
    int ret;

    /* Select the right mux port and perform the transfer. */

    ret = priv->select(parent, priv->mux_priv, priv->chan_id);
    if (ret >= 0)
        ret = parent->algo->smbus_xfer(parent, addr, flags,
                    read_write, command, size, data);
    if (priv->deselect)
        priv->deselect(parent, priv->mux_priv, priv->chan_id);

    return ret;
}

/* Return the parent's functionality */
static u32 i2c_mux_functionality(struct i2c_adapter *adap)
{
    struct i2c_mux_priv *priv = adap->algo_data;
    struct i2c_adapter *parent = priv->parent;

    return parent->algo->functionality(parent);
}

/* Return all parent classes, merged */
static unsigned int i2c_mux_parent_classes(struct i2c_adapter *parent)
{
    unsigned int class = 0;

    do {
        class |= parent->class;
        parent = i2c_parent_is_i2c_adapter(parent);
    } while (parent);

    return class;
}

struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
                struct device *mux_dev,
                void *mux_priv, u32 force_nr, u32 chan_id,
                unsigned int class,
                int (*select) (struct i2c_adapter *,
                           void *, u32),
                int (*deselect) (struct i2c_adapter *,
                         void *, u32))
{
    struct i2c_mux_priv *priv;
    int ret;

    priv = kzalloc(sizeof(struct i2c_mux_priv), GFP_KERNEL);
    if (!priv)
        return NULL;

    /* Set up private adapter data */
    priv->parent = parent;
    priv->mux_priv = mux_priv;
    priv->chan_id = chan_id;
    priv->select = select;
    priv->deselect = deselect;

    /* Need to do algo dynamically because we don't know ahead
     * of time what sort of physical adapter we'll be dealing with.
     */
    if (parent->algo->master_xfer)
        priv->algo.master_xfer = i2c_mux_master_xfer;
    if (parent->algo->smbus_xfer)
        priv->algo.smbus_xfer = i2c_mux_smbus_xfer;
    priv->algo.functionality = i2c_mux_functionality;

    /* Now fill out new adapter structure */
    snprintf(priv->adap.name, sizeof(priv->adap.name),
         "i2c-%d-mux (chan_id %d)", i2c_adapter_id(parent), chan_id);
    priv->adap.owner = THIS_MODULE;
    priv->adap.algo = &priv->algo;
    priv->adap.algo_data = priv;
    priv->adap.dev.parent = &parent->dev;

    /* Sanity check on class */
    if (i2c_mux_parent_classes(parent) & class)
        dev_err(&parent->dev,
            "Segment %d behind mux can't share classes with ancestors\n",
            chan_id);
    else
        priv->adap.class = class;

    /*
     * Try to populate the mux adapter's of_node, expands to
     * nothing if !CONFIG_OF.
     */
    if (mux_dev->of_node) {
        struct device_node *child;
        u32 reg;

        for_each_child_of_node(mux_dev->of_node, child) {
            ret = of_property_read_u32(child, "reg", &reg);
            if (ret)
                continue;
            if (chan_id == reg) {
                priv->adap.dev.of_node = child;
                break;
            }
        }
    }

    if (force_nr) {
        priv->adap.nr = force_nr;
        ret = i2c_add_numbered_adapter(&priv->adap);
    } else {
        ret = i2c_add_adapter(&priv->adap);
    }
    if (ret < 0) {
        dev_err(&parent->dev,
            "failed to add mux-adapter (error=%d)\n",
            ret);
        kfree(priv);
        return NULL;
    }

    dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
         i2c_adapter_id(&priv->adap));

    of_i2c_register_devices(&priv->adap);

    return &priv->adap;
}
EXPORT_SYMBOL_GPL(i2c_add_mux_adapter);

int i2c_del_mux_adapter(struct i2c_adapter *adap)
{
    struct i2c_mux_priv *priv = adap->algo_data;
    int ret;

    ret = i2c_del_adapter(adap);
    if (ret < 0)
        return ret;
    kfree(priv);

    return 0;
}
EXPORT_SYMBOL_GPL(i2c_del_mux_adapter);

MODULE_AUTHOR("Rodolfo Giometti <[email protected]>");
MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
MODULE_LICENSE("GPL v2");