linux-imx

/*

 * ST Random Number Generator Driver ST's Platforms

 *

 * Author: Pankaj Dev: <pankaj.dev@st.com>

 *         Lee Jones <lee.jones@linaro.org>

 *

 * Copyright (C) 2015 STMicroelectronics (R&D) Limited

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 */

​

#include <linux/clk.h>

#include <linux/delay.h>

#include <linux/hw_random.h>

#include <linux/io.h>

#include <linux/module.h>

#include <linux/of.h>

#include <linux/platform_device.h>

#include <linux/slab.h>

​

/* Registers */

#define ST_RNG_STATUS_REG       0x20

#define ST_RNG_DATA_REG         0x24

​

/* Registers fields */

#define ST_RNG_STATUS_BAD_SEQUENCE  BIT(0)

#define ST_RNG_STATUS_BAD_ALTERNANCE    BIT(1)

#define ST_RNG_STATUS_FIFO_FULL     BIT(5)

​

#define ST_RNG_SAMPLE_SIZE      2 /* 2 Byte (16bit) samples */

#define ST_RNG_FIFO_DEPTH       4

#define ST_RNG_FIFO_SIZE        (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)

​

/*

 * Samples are documented to be available every 0.667us, so in theory

 * the 4 sample deep FIFO should take 2.668us to fill.  However, during

 * thorough testing, it became apparent that filling the FIFO actually

 * takes closer to 12us.  We then multiply by 2 in order to account for

 * the lack of udelay()'s reliability, suggested by Russell King.

 */

#define ST_RNG_FILL_FIFO_TIMEOUT    (12 * 2)

​

struct st_rng_data {

    void __iomem    *base;

    struct clk  *clk;

    struct hwrng    ops;

};

​

static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)

{

    struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;

    u32 status;

    int i;

​

    /* Wait until FIFO is full - max 4uS*/

    for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {

        status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);

        if (status & ST_RNG_STATUS_FIFO_FULL)

            break;

        udelay(1);

    }