/*
 * SPI slave handler controlling system state
 *
 * This SPI slave handler allows remote control of system reboot, power off,
 * halt, and suspend.
 *
 * Copyright (C) 2016-2017 Glider bvba
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Usage (assuming /dev/spidev2.0 corresponds to the SPI master on the remote
 * system):
 *
 *   # reboot='\x7c\x50'
 *   # poweroff='\x71\x3f'
 *   # halt='\x38\x76'
 *   # suspend='\x1b\x1b'
 *   # spidev_test -D /dev/spidev2.0 -p $suspend # or $reboot, $poweroff, $halt
 */

#include <linux/completion.h>
#include <linux/module.h>
#include <linux/reboot.h>
#include <linux/suspend.h>
#include <linux/spi/spi.h>

/*
 * The numbers are chosen to display something human-readable on two 7-segment
 * displays connected to two 74HC595 shift registers
 */
#define CMD_REBOOT      0x7c50  /* rb */
#define CMD_POWEROFF    0x713f  /* OF */
#define CMD_HALT        0x3876  /* HL */
#define CMD_SUSPEND     0x1b1b  /* ZZ */

struct spi_slave_system_control_priv {
        struct spi_device *spi;
        struct completion finished;
        struct spi_transfer xfer;
        struct spi_message msg;
        __be16 cmd;
};

static
int spi_slave_system_control_submit(struct spi_slave_system_control_priv *priv);

static void spi_slave_system_control_complete(void *arg)
{
        struct spi_slave_system_control_priv *priv = arg;
        u16 cmd;
        int ret;

        if (priv->msg.status)
                goto terminate;

        cmd = be16_to_cpu(priv->cmd);
        switch (cmd) {
        case CMD_REBOOT:
                dev_info(&priv->spi->dev, "Rebooting system...\n");
                kernel_restart(NULL);
                break;

        case CMD_POWEROFF:
                dev_info(&priv->spi->dev, "Powering off system...\n");
                kernel_power_off();
                break;

        case CMD_HALT:
                dev_info(&priv->spi->dev, "Halting system...\n");
                kernel_halt();
                break;

        case CMD_SUSPEND:
                dev_info(&priv->spi->dev, "Suspending system...\n");
                pm_suspend(PM_SUSPEND_MEM);
                break;

        default:
                dev_warn(&priv->spi->dev, "Unknown command 0x%x\n", cmd);
                break;
        }

        ret = spi_slave_system_control_submit(priv);
        if (ret)
                goto terminate;

        return;

terminate:
        dev_info(&priv->spi->dev, "Terminating\n");
        complete(&priv->finished);
}

static
int spi_slave_system_control_submit(struct spi_slave_system_control_priv *priv)
{
        int ret;

        spi_message_init_with_transfers(&priv->msg, &priv->xfer, 1);

        priv->msg.complete = spi_slave_system_control_complete;
        priv->msg.context = priv;

        ret = spi_async(priv->spi, &priv->msg);
        if (ret)
                dev_err(&priv->spi->dev, "spi_async() failed %d\n", ret);

        return ret;
}

static int spi_slave_system_control_probe(struct spi_device *spi)
{
        struct spi_slave_system_control_priv *priv;
        int ret;

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

        priv->spi = spi;
        init_completion(&priv->finished);
        priv->xfer.rx_buf = &priv->cmd;
        priv->xfer.len = sizeof(priv->cmd);

        ret = spi_slave_system_control_submit(priv);
        if (ret)
                return ret;

        spi_set_drvdata(spi, priv);
        return 0;
}

static void spi_slave_system_control_remove(struct spi_device *spi)
{
        struct spi_slave_system_control_priv *priv = spi_get_drvdata(spi);

        spi_target_abort(spi);
        wait_for_completion(&priv->finished);
}

static struct spi_driver spi_slave_system_control_driver = {
        .driver = {
                .name   = "spi-slave-system-control",
        },
        .probe          = spi_slave_system_control_probe,
        .remove         = spi_slave_system_control_remove,
};
module_spi_driver(spi_slave_system_control_driver);

MODULE_AUTHOR("Geert Uytterhoeven <geert+renesas@glider.be>");
MODULE_DESCRIPTION("SPI slave handler controlling system state");
MODULE_LICENSE("GPL v2");