// SPDX-License-Identifier: GPL-2.0
//
// General Purpose SPI multiplexer

#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mux/consumer.h>
#include <linux/slab.h>
#include <linux/spi/spi.h>

#define SPI_MUX_NO_CS   ((unsigned int)-1)

/**
 * DOC: Driver description
 *
 * This driver supports a MUX on an SPI bus. This can be useful when you need
 * more chip selects than the hardware peripherals support, or than are
 * available in a particular board setup.
 *
 * The driver will create an additional SPI controller. Devices added under the
 * mux will be handled as 'chip selects' on this controller.
 */

/**
 * struct spi_mux_priv - the basic spi_mux structure
 * @spi:                pointer to the device struct attached to the parent
 *                      spi controller
 * @current_cs:         The current chip select set in the mux
 * @child_msg_complete: The mux replaces the complete callback in the child's
 *                      message to its own callback; this field is used by the
 *                      driver to store the child's callback during a transfer
 * @child_msg_context:  Used to store the child's context to the callback
 * @child_msg_dev:      Used to store the spi_device pointer to the child
 * @mux:                mux_control structure used to provide chip selects for
 *                      downstream spi devices
 */
struct spi_mux_priv {
        struct spi_device       *spi;
        unsigned int            current_cs;

        void                    (*child_msg_complete)(void *context);
        void                    *child_msg_context;
        struct spi_device       *child_msg_dev;
        struct mux_control      *mux;
};

/* should not get called when the parent controller is doing a transfer */
static int spi_mux_select(struct spi_device *spi)
{
        struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
        int ret;

        ret = mux_control_select(priv->mux, spi_get_chipselect(spi, 0));
        if (ret)
                return ret;

        if (priv->current_cs == spi_get_chipselect(spi, 0))
                return 0;

        dev_dbg(&priv->spi->dev, "setting up the mux for cs %d\n",
                spi_get_chipselect(spi, 0));

        /* copy the child device's settings except for the cs */
        priv->spi->max_speed_hz = spi->max_speed_hz;
        priv->spi->mode = spi->mode;
        priv->spi->bits_per_word = spi->bits_per_word;

        priv->current_cs = spi_get_chipselect(spi, 0);

        return spi_setup(priv->spi);
}

static int spi_mux_setup(struct spi_device *spi)
{
        struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);

        /*
         * can be called multiple times, won't do a valid setup now but we will
         * change the settings when we do a transfer (necessary because we
         * can't predict from which device it will be anyway)
         */
        return spi_setup(priv->spi);
}

static void spi_mux_complete_cb(void *context)
{
        struct spi_mux_priv *priv = (struct spi_mux_priv *)context;
        struct spi_controller *ctlr = spi_get_drvdata(priv->spi);
        struct spi_message *m = ctlr->cur_msg;

        m->complete = priv->child_msg_complete;
        m->context = priv->child_msg_context;
        m->spi = priv->child_msg_dev;
        spi_finalize_current_message(ctlr);
        mux_control_deselect(priv->mux);
}

static int spi_mux_transfer_one_message(struct spi_controller *ctlr,
                                                struct spi_message *m)
{
        struct spi_mux_priv *priv = spi_controller_get_devdata(ctlr);
        struct spi_device *spi = m->spi;
        int ret;

        ret = spi_mux_select(spi);
        if (ret)
                return ret;

        /*
         * Replace the complete callback, context and spi_device with our own
         * pointers. Save originals
         */
        priv->child_msg_complete = m->complete;
        priv->child_msg_context = m->context;
        priv->child_msg_dev = m->spi;

        m->complete = spi_mux_complete_cb;
        m->context = priv;
        m->spi = priv->spi;

        /* do the transfer */
        return spi_async(priv->spi, m);
}

static int spi_mux_probe(struct spi_device *spi)
{
        struct spi_controller *ctlr;
        struct spi_mux_priv *priv;
        int ret;

        ctlr = spi_alloc_host(&spi->dev, sizeof(*priv));
        if (!ctlr)
                return -ENOMEM;

        spi_set_drvdata(spi, ctlr);
        priv = spi_controller_get_devdata(ctlr);
        priv->spi = spi;

        /*
         * Increase lockdep class as these lock are taken while the parent bus
         * already holds their instance's lock.
         */
        lockdep_set_subclass(&ctlr->io_mutex, 1);
        lockdep_set_subclass(&ctlr->add_lock, 1);

        priv->mux = devm_mux_control_get(&spi->dev, NULL);
        if (IS_ERR(priv->mux)) {
                ret = dev_err_probe(&spi->dev, PTR_ERR(priv->mux),
                                    "failed to get control-mux\n");
                goto err_put_ctlr;
        }

        priv->current_cs = SPI_MUX_NO_CS;

        /* supported modes are the same as our parent's */
        ctlr->mode_bits = spi->controller->mode_bits;
        ctlr->flags = spi->controller->flags;
        ctlr->bits_per_word_mask = spi->controller->bits_per_word_mask;
        ctlr->transfer_one_message = spi_mux_transfer_one_message;
        ctlr->setup = spi_mux_setup;
        ctlr->num_chipselect = mux_control_states(priv->mux);
        ctlr->bus_num = -1;
        ctlr->must_async = true;
        ctlr->defer_optimize_message = true;

        ret = devm_spi_register_controller(&spi->dev, ctlr);
        if (ret)
                goto err_put_ctlr;

        return 0;

err_put_ctlr:
        spi_controller_put(ctlr);

        return ret;
}

static const struct spi_device_id spi_mux_id[] = {
        { "spi-mux" },
        { }
};
MODULE_DEVICE_TABLE(spi, spi_mux_id);

static const struct of_device_id spi_mux_of_match[] = {
        { .compatible = "spi-mux" },
        { }
};
MODULE_DEVICE_TABLE(of, spi_mux_of_match);

static struct spi_driver spi_mux_driver = {
        .probe  = spi_mux_probe,
        .driver = {
                .name   = "spi-mux",
                .of_match_table = spi_mux_of_match,
        },
        .id_table = spi_mux_id,
};

module_spi_driver(spi_mux_driver);

MODULE_DESCRIPTION("SPI multiplexer");
MODULE_LICENSE("GPL");