/*
 * Allwinner sunXi SoCs Security ID support.
 *
 * Copyright (c) 2013 Oliver Schinagl <oliver@schinagl.nl>
 * Copyright (C) 2014 Maxime Ripard <maxime.ripard@free-electrons.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/device.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/module.h>
#include <linux/nvmem-provider.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/random.h>

/* Registers and special values for doing register-based SID readout on H3 */
#define SUN8I_SID_PRCTL         0x40
#define SUN8I_SID_RDKEY         0x60

#define SUN8I_SID_OFFSET_MASK   0x1FF
#define SUN8I_SID_OFFSET_SHIFT  16
#define SUN8I_SID_OP_LOCK       (0xAC << 8)
#define SUN8I_SID_READ          BIT(1)

static struct nvmem_config econfig = {
        .name = "sunxi-sid",
        .read_only = true,
        .stride = 4,
        .word_size = 1,
};

struct sunxi_sid_cfg {
        u32     value_offset;
        u32     size;
        bool    need_register_readout;
};

struct sunxi_sid {
        void __iomem            *base;
        u32                     value_offset;
};

/* We read the entire key, due to a 32 bit read alignment requirement. Since we
 * want to return the requested byte, this results in somewhat slower code and
 * uses 4 times more reads as needed but keeps code simpler. Since the SID is
 * only very rarely probed, this is not really an issue.
 */
static u8 sunxi_sid_read_byte(const struct sunxi_sid *sid,
                              const unsigned int offset)
{
        u32 sid_key;

        sid_key = ioread32be(sid->base + round_down(offset, 4));
        sid_key >>= (offset % 4) * 8;

        return sid_key; /* Only return the last byte */
}

static int sunxi_sid_read(void *context, unsigned int offset,
                          void *val, size_t bytes)
{
        struct sunxi_sid *sid = context;
        u8 *buf = val;

        /* Offset the read operation to the real position of SID */
        offset += sid->value_offset;

        while (bytes--)
                *buf++ = sunxi_sid_read_byte(sid, offset++);

        return 0;
}

static int sun8i_sid_register_readout(const struct sunxi_sid *sid,
                                      const unsigned int offset,
                                      u32 *out)
{
        u32 reg_val;
        int ret;

        /* Set word, lock access, and set read command */
        reg_val = (offset & SUN8I_SID_OFFSET_MASK)
                  << SUN8I_SID_OFFSET_SHIFT;
        reg_val |= SUN8I_SID_OP_LOCK | SUN8I_SID_READ;
        writel(reg_val, sid->base + SUN8I_SID_PRCTL);

        ret = readl_poll_timeout(sid->base + SUN8I_SID_PRCTL, reg_val,
                                 !(reg_val & SUN8I_SID_READ), 100, 250000);
        if (ret)
                return ret;

        if (out)
                *out = readl(sid->base + SUN8I_SID_RDKEY);

        writel(0, sid->base + SUN8I_SID_PRCTL);

        return 0;
}

/*
 * On Allwinner H3, the value on the 0x200 offset of the SID controller seems
 * to be not reliable at all.
 * Read by the registers instead.
 */
static int sun8i_sid_read_byte_by_reg(const struct sunxi_sid *sid,
                                      const unsigned int offset,
                                      u8 *out)
{
        u32 word;
        int ret;

        ret = sun8i_sid_register_readout(sid, offset & ~0x03, &word);

        if (ret)
                return ret;

        *out = (word >> ((offset & 0x3) * 8)) & 0xff;

        return 0;
}

static int sun8i_sid_read_by_reg(void *context, unsigned int offset,
                                 void *val, size_t bytes)
{
        struct sunxi_sid *sid = context;
        u8 *buf = val;
        int ret;

        while (bytes--) {
                ret = sun8i_sid_read_byte_by_reg(sid, offset++, buf++);
                if (ret)
                        return ret;
        }

        return 0;
}

static int sunxi_sid_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct resource *res;
        struct nvmem_device *nvmem;
        struct sunxi_sid *sid;
        int ret, i, size;
        char *randomness;
        const struct sunxi_sid_cfg *cfg;

        sid = devm_kzalloc(dev, sizeof(*sid), GFP_KERNEL);
        if (!sid)
                return -ENOMEM;

        cfg = of_device_get_match_data(dev);
        if (!cfg)
                return -EINVAL;
        sid->value_offset = cfg->value_offset;

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        sid->base = devm_ioremap_resource(dev, res);
        if (IS_ERR(sid->base))
                return PTR_ERR(sid->base);

        size = cfg->size;

        econfig.size = size;
        econfig.dev = dev;
        if (cfg->need_register_readout)
                econfig.reg_read = sun8i_sid_read_by_reg;
        else
                econfig.reg_read = sunxi_sid_read;
        econfig.priv = sid;
        nvmem = nvmem_register(&econfig);
        if (IS_ERR(nvmem))
                return PTR_ERR(nvmem);

        randomness = kzalloc(size, GFP_KERNEL);
        if (!randomness) {
                ret = -EINVAL;
                goto err_unreg_nvmem;
        }

        for (i = 0; i < size; i++)
                econfig.reg_read(sid, i, &randomness[i], 1);

        add_device_randomness(randomness, size);
        kfree(randomness);

        platform_set_drvdata(pdev, nvmem);

        return 0;

err_unreg_nvmem:
        nvmem_unregister(nvmem);
        return ret;
}

static int sunxi_sid_remove(struct platform_device *pdev)
{
        struct nvmem_device *nvmem = platform_get_drvdata(pdev);

        return nvmem_unregister(nvmem);
}

static const struct sunxi_sid_cfg sun4i_a10_cfg = {
        .size = 0x10,
};

static const struct sunxi_sid_cfg sun7i_a20_cfg = {
        .size = 0x200,
};

static const struct sunxi_sid_cfg sun8i_h3_cfg = {
        .value_offset = 0x200,
        .size = 0x100,
        .need_register_readout = true,
};

static const struct sunxi_sid_cfg sun50i_a64_cfg = {
        .value_offset = 0x200,
        .size = 0x100,
};

static const struct of_device_id sunxi_sid_of_match[] = {
        { .compatible = "allwinner,sun4i-a10-sid", .data = &sun4i_a10_cfg },
        { .compatible = "allwinner,sun7i-a20-sid", .data = &sun7i_a20_cfg },
        { .compatible = "allwinner,sun8i-h3-sid", .data = &sun8i_h3_cfg },
        { .compatible = "allwinner,sun50i-a64-sid", .data = &sun50i_a64_cfg },
        {/* sentinel */},
};
MODULE_DEVICE_TABLE(of, sunxi_sid_of_match);

static struct platform_driver sunxi_sid_driver = {
        .probe = sunxi_sid_probe,
        .remove = sunxi_sid_remove,
        .driver = {
                .name = "eeprom-sunxi-sid",
                .of_match_table = sunxi_sid_of_match,
        },
};
module_platform_driver(sunxi_sid_driver);

MODULE_AUTHOR("Oliver Schinagl <oliver@schinagl.nl>");
MODULE_DESCRIPTION("Allwinner sunxi security id driver");
MODULE_LICENSE("GPL");