// SPDX-License-Identifier: GPL-2.0
/*
 * Microchip / Atmel SHA204A (I2C) driver.
 *
 * Copyright (c) 2019 Linaro, Ltd. <ard.biesheuvel@linaro.org>
 */

#include <linux/delay.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
#include <linux/workqueue.h>
#include "atmel-i2c.h"

/*
 * According to review by Bill Cox [1], the ATSHA204 has very low entropy.
 * [1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html
 */
static const unsigned short atsha204_quality = 1;

static void atmel_sha204a_rng_done(struct atmel_i2c_work_data *work_data,
				   void *areq, int status)
{
	struct atmel_i2c_client_priv *i2c_priv = work_data->ctx;
	struct hwrng *rng = areq;

	if (status) {
		dev_warn_ratelimited(&i2c_priv->client->dev,
				     "i2c transaction failed (%d)\n",
				     status);
		kfree(work_data);
		atomic_dec(&i2c_priv->tfm_count);
		return;
	}

	rng->priv = (unsigned long)work_data;
	atomic_dec(&i2c_priv->tfm_count);
}

static int atmel_sha204a_rng_read_nonblocking(struct hwrng *rng, void *data,
					      size_t max)
{
	struct atmel_i2c_client_priv *i2c_priv;
	struct atmel_i2c_work_data *work_data;

	i2c_priv = container_of(rng, struct atmel_i2c_client_priv, hwrng);

	/* keep maximum 1 asynchronous read in flight at any time */
	if (!atomic_add_unless(&i2c_priv->tfm_count, 1, 1))
		return 0;

	if (rng->priv) {
		work_data = (struct atmel_i2c_work_data *)rng->priv;
		max = min(RANDOM_RSP_SIZE - CMD_OVERHEAD_SIZE, max);
		memcpy(data, &work_data->cmd.data[RSP_DATA_IDX], max);
		rng->priv = 0;
	} else {
		work_data = kmalloc_obj(*work_data, GFP_ATOMIC);
		if (!work_data) {
			atomic_dec(&i2c_priv->tfm_count);
			return -ENOMEM;
		}
		work_data->ctx = i2c_priv;
		work_data->client = i2c_priv->client;

		max = 0;
	}

	atmel_i2c_init_random_cmd(&work_data->cmd);
	atmel_i2c_enqueue(work_data, atmel_sha204a_rng_done, rng);

	return max;
}

static int atmel_sha204a_rng_read(struct hwrng *rng, void *data, size_t max,
				  bool wait)
{
	struct atmel_i2c_client_priv *i2c_priv;
	struct atmel_i2c_cmd cmd;
	int ret;

	if (!wait)
		return atmel_sha204a_rng_read_nonblocking(rng, data, max);

	i2c_priv = container_of(rng, struct atmel_i2c_client_priv, hwrng);

	atmel_i2c_init_random_cmd(&cmd);

	ret = atmel_i2c_send_receive(i2c_priv->client, &cmd);
	if (ret)
		return ret;

	max = min(RANDOM_RSP_SIZE - CMD_OVERHEAD_SIZE, max);
	memcpy(data, &cmd.data[RSP_DATA_IDX], max);

	return max;
}

static int atmel_sha204a_otp_read(struct i2c_client *client, u16 addr, u8 *otp)
{
	struct atmel_i2c_cmd cmd;
	int ret;

	ret = atmel_i2c_init_read_otp_cmd(&cmd, addr);
	if (ret < 0) {
		dev_err(&client->dev, "failed, invalid otp address %04X\n",
			addr);
		return ret;
	}

	ret = atmel_i2c_send_receive(client, &cmd);
	if (ret < 0) {
		dev_err(&client->dev, "failed to read otp at %04X\n", addr);
		return ret;
	}

	if (cmd.data[0] == 0xff) {
		dev_err(&client->dev, "failed, device not ready\n");
		return -EIO;
	}

	memcpy(otp, cmd.data+1, 4);

	return ret;
}

static ssize_t otp_show(struct device *dev,
			struct device_attribute *attr, char *buf)
{
	u16 addr;
	u8 otp[OTP_ZONE_SIZE];
	struct i2c_client *client = to_i2c_client(dev);
	ssize_t len = 0;
	int i, ret;

	for (addr = 0; addr < OTP_ZONE_SIZE / 4; addr++) {
		ret = atmel_sha204a_otp_read(client, addr, otp + addr * 4);
		if (ret < 0) {
			dev_err(dev, "failed to read otp zone\n");
			return ret;
		}
	}

	for (i = 0; i < OTP_ZONE_SIZE; i++)
		len += sysfs_emit_at(buf, len, "%02X", otp[i]);
	len += sysfs_emit_at(buf, len, "\n");
	return len;
}
static DEVICE_ATTR_RO(otp);

static struct attribute *atmel_sha204a_attrs[] = {
	&dev_attr_otp.attr,
	NULL
};

static const struct attribute_group atmel_sha204a_groups = {
	.name = "atsha204a",
	.attrs = atmel_sha204a_attrs,
};

static int atmel_sha204a_probe(struct i2c_client *client)
{
	struct atmel_i2c_client_priv *i2c_priv;
	const unsigned short *quality;
	int ret;

	ret = atmel_i2c_probe(client);
	if (ret)
		return ret;

	i2c_priv = i2c_get_clientdata(client);

	memset(&i2c_priv->hwrng, 0, sizeof(i2c_priv->hwrng));

	i2c_priv->hwrng.name = dev_name(&client->dev);
	i2c_priv->hwrng.read = atmel_sha204a_rng_read;

	quality = i2c_get_match_data(client);
	if (quality)
		i2c_priv->hwrng.quality = *quality;

	ret = devm_hwrng_register(&client->dev, &i2c_priv->hwrng);
	if (ret) {
		dev_err(&client->dev, "failed to register RNG (%d)\n", ret);
		return ret;
	}

	ret = sysfs_create_group(&client->dev.kobj, &atmel_sha204a_groups);
	if (ret) {
		dev_err(&client->dev, "failed to create sysfs group (%d)\n", ret);
		return ret;
	}

	return ret;
}

static void atmel_sha204a_remove(struct i2c_client *client)
{
	struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);

	sysfs_remove_group(&client->dev.kobj, &atmel_sha204a_groups);
	devm_hwrng_unregister(&client->dev, &i2c_priv->hwrng);
	atmel_i2c_flush_queue();

	kfree((void *)i2c_priv->hwrng.priv);
}

static const struct of_device_id atmel_sha204a_dt_ids[] = {
	{ .compatible = "atmel,atsha204" },
	{ .compatible = "atmel,atsha204a" },
	{ }
};
MODULE_DEVICE_TABLE(of, atmel_sha204a_dt_ids);

static const struct i2c_device_id atmel_sha204a_id[] = {
	{ .name = "atsha204", .driver_data = (kernel_ulong_t)&atsha204_quality },
	{ .name = "atsha204a", .driver_data = (kernel_ulong_t)NULL },
	{ }
};
MODULE_DEVICE_TABLE(i2c, atmel_sha204a_id);

static struct i2c_driver atmel_sha204a_driver = {
	.probe			= atmel_sha204a_probe,
	.remove			= atmel_sha204a_remove,
	.id_table		= atmel_sha204a_id,

	.driver.name		= "atmel-sha204a",
	.driver.of_match_table	= atmel_sha204a_dt_ids,
};

static int __init atmel_sha204a_init(void)
{
	return i2c_add_driver(&atmel_sha204a_driver);
}

static void __exit atmel_sha204a_exit(void)
{
	atmel_i2c_flush_queue();
	i2c_del_driver(&atmel_sha204a_driver);
}

module_init(atmel_sha204a_init);
module_exit(atmel_sha204a_exit);

MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
MODULE_DESCRIPTION("Microchip / Atmel SHA204A (I2C) driver");
MODULE_LICENSE("GPL v2");