1 /* 2 * ST Random Number Generator Driver ST's Platforms 3 * 4 * Author: Pankaj Dev: <pankaj.dev@st.com> 5 * Lee Jones <lee.jones@linaro.org> 6 * 7 * Copyright (C) 2015 STMicroelectronics (R&D) Limited 8 * 9 * This program is free software; you can redistribute it and/or modify 10 * it under the terms of the GNU General Public License version 2 as 11 * published by the Free Software Foundation. 12 */ 13 14 #include <linux/clk.h> 15 #include <linux/delay.h> 16 #include <linux/hw_random.h> 17 #include <linux/io.h> 18 #include <linux/module.h> 19 #include <linux/of.h> 20 #include <linux/platform_device.h> 21 #include <linux/slab.h> 22 23 /* Registers */ 24 #define ST_RNG_STATUS_REG 0x20 25 #define ST_RNG_DATA_REG 0x24 26 27 /* Registers fields */ 28 #define ST_RNG_STATUS_BAD_SEQUENCE BIT(0) 29 #define ST_RNG_STATUS_BAD_ALTERNANCE BIT(1) 30 #define ST_RNG_STATUS_FIFO_FULL BIT(5) 31 32 #define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */ 33 #define ST_RNG_FIFO_DEPTH 4 34 #define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE) 35 36 /* 37 * Samples are documented to be available every 0.667us, so in theory 38 * the 4 sample deep FIFO should take 2.668us to fill. However, during 39 * thorough testing, it became apparent that filling the FIFO actually 40 * takes closer to 12us. We then multiply by 2 in order to account for 41 * the lack of udelay()'s reliability, suggested by Russell King. 42 */ 43 #define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2) 44 45 struct st_rng_data { 46 void __iomem *base; 47 struct clk *clk; 48 struct hwrng ops; 49 }; 50 51 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait) 52 { 53 struct st_rng_data *ddata = (struct st_rng_data *)rng->priv; 54 u32 status; 55 int i; 56 57 /* Wait until FIFO is full - max 4uS*/ 58 for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) { 59 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG); 60 if (status & ST_RNG_STATUS_FIFO_FULL) 61 break; 62 udelay(1); 63 } 64 65 if (i == ST_RNG_FILL_FIFO_TIMEOUT) 66 return 0; 67 68 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2) 69 *(u16 *)(data + i) = 70 readl_relaxed(ddata->base + ST_RNG_DATA_REG); 71 72 return i; /* No of bytes read */ 73 } 74 75 static int st_rng_probe(struct platform_device *pdev) 76 { 77 struct st_rng_data *ddata; 78 struct resource *res; 79 struct clk *clk; 80 void __iomem *base; 81 int ret; 82 83 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL); 84 if (!ddata) 85 return -ENOMEM; 86 87 res = platform_get_resource(pdev, IORESOURCE_MEM, 0); 88 base = devm_ioremap_resource(&pdev->dev, res); 89 if (IS_ERR(base)) 90 return PTR_ERR(base); 91 92 clk = devm_clk_get(&pdev->dev, NULL); 93 if (IS_ERR(clk)) 94 return PTR_ERR(clk); 95 96 ret = clk_prepare_enable(clk); 97 if (ret) 98 return ret; 99 100 ddata->ops.priv = (unsigned long)ddata; 101 ddata->ops.read = st_rng_read; 102 ddata->ops.name = pdev->name; 103 ddata->base = base; 104 ddata->clk = clk; 105 106 dev_set_drvdata(&pdev->dev, ddata); 107 108 ret = hwrng_register(&ddata->ops); 109 if (ret) { 110 dev_err(&pdev->dev, "Failed to register HW RNG\n"); 111 return ret; 112 } 113 114 dev_info(&pdev->dev, "Successfully registered HW RNG\n"); 115 116 return 0; 117 } 118 119 static int st_rng_remove(struct platform_device *pdev) 120 { 121 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev); 122 123 hwrng_unregister(&ddata->ops); 124 125 clk_disable_unprepare(ddata->clk); 126 127 return 0; 128 } 129 130 static const struct of_device_id st_rng_match[] = { 131 { .compatible = "st,rng" }, 132 {}, 133 }; 134 MODULE_DEVICE_TABLE(of, st_rng_match); 135 136 static struct platform_driver st_rng_driver = { 137 .driver = { 138 .name = "st-hwrandom", 139 .of_match_table = of_match_ptr(st_rng_match), 140 }, 141 .probe = st_rng_probe, 142 .remove = st_rng_remove 143 }; 144 145 module_platform_driver(st_rng_driver); 146 147 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>"); 148 MODULE_LICENSE("GPL v2"); 149