// SPDX-License-Identifier: GPL-2.0
/*
 * LiteX SoC Controller Driver
 *
 * Copyright (C) 2020 Antmicro <www.antmicro.com>
 *
 */

#include <linux/litex.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/printk.h>
#include <linux/module.h>
#include <linux/io.h>
#include <linux/reboot.h>

/* reset register located at the base address */
#define RESET_REG_OFF           0x00
#define RESET_REG_VALUE         0x00000001

#define SCRATCH_REG_OFF         0x04
#define SCRATCH_REG_VALUE       0x12345678
#define SCRATCH_TEST_VALUE      0xdeadbeef

/*
 * Check LiteX CSR read/write access
 *
 * This function reads and writes a scratch register in order to verify if CSR
 * access works.
 *
 * In case any problems are detected, the driver should panic.
 *
 * Access to the LiteX CSR is, by design, done in CPU native endianness.
 * The driver should not dynamically configure access functions when
 * the endianness mismatch is detected. Such situation indicates problems in
 * the soft SoC design and should be solved at the LiteX generator level,
 * not in the software.
 */
static int litex_check_csr_access(void __iomem *reg_addr)
{
        unsigned long reg;

        reg = litex_read32(reg_addr + SCRATCH_REG_OFF);

        if (reg != SCRATCH_REG_VALUE) {
                panic("Scratch register read error - the system is probably broken! Expected: 0x%x but got: 0x%lx",
                        SCRATCH_REG_VALUE, reg);
                return -EINVAL;
        }

        litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_TEST_VALUE);
        reg = litex_read32(reg_addr + SCRATCH_REG_OFF);

        if (reg != SCRATCH_TEST_VALUE) {
                panic("Scratch register write error - the system is probably broken! Expected: 0x%x but got: 0x%lx",
                        SCRATCH_TEST_VALUE, reg);
                return -EINVAL;
        }

        /* restore original value of the SCRATCH register */
        litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_VALUE);

        pr_info("LiteX SoC Controller driver initialized");

        return 0;
}

struct litex_soc_ctrl_device {
        void __iomem *base;
};

static int litex_reset_handler(struct sys_off_data *data)
{
        struct litex_soc_ctrl_device *soc_ctrl_dev = data->cb_data;

        litex_write32(soc_ctrl_dev->base + RESET_REG_OFF, RESET_REG_VALUE);
        return NOTIFY_DONE;
}

static const struct of_device_id litex_soc_ctrl_of_match[] = {
        {.compatible = "litex,soc-controller"},
        {},
};
MODULE_DEVICE_TABLE(of, litex_soc_ctrl_of_match);

static int litex_soc_ctrl_probe(struct platform_device *pdev)
{
        struct litex_soc_ctrl_device *soc_ctrl_dev;
        int error;

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

        soc_ctrl_dev->base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(soc_ctrl_dev->base))
                return PTR_ERR(soc_ctrl_dev->base);

        error = litex_check_csr_access(soc_ctrl_dev->base);
        if (error)
                return error;

        error = devm_register_restart_handler(&pdev->dev,
                                              litex_reset_handler,
                                              soc_ctrl_dev);
        if (error) {
                dev_warn(&pdev->dev, "cannot register restart handler: %d\n",
                         error);
        }

        return 0;
}

static struct platform_driver litex_soc_ctrl_driver = {
        .driver = {
                .name = "litex-soc-controller",
                .of_match_table = litex_soc_ctrl_of_match,
        },
        .probe = litex_soc_ctrl_probe,
};

module_platform_driver(litex_soc_ctrl_driver);
MODULE_DESCRIPTION("LiteX SoC Controller driver");
MODULE_AUTHOR("Antmicro <www.antmicro.com>");
MODULE_LICENSE("GPL v2");