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 if (max < sizeof(u16)) 58 return -EINVAL; 59 60 /* Wait until FIFO is full - max 4uS*/ 61 for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) { 62 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG); 63 if (status & ST_RNG_STATUS_FIFO_FULL) 64 break; 65 udelay(1); 66 } 67 68 if (i == ST_RNG_FILL_FIFO_TIMEOUT) 69 return 0; 70 71 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2) 72 *(u16 *)(data + i) = 73 readl_relaxed(ddata->base + ST_RNG_DATA_REG); 74 75 return i; /* No of bytes read */ 76 } 77 78 static int st_rng_probe(struct platform_device *pdev) 79 { 80 struct st_rng_data *ddata; 81 struct resource *res; 82 struct clk *clk; 83 void __iomem *base; 84 int ret; 85 86 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL); 87 if (!ddata) 88 return -ENOMEM; 89 90 res = platform_get_resource(pdev, IORESOURCE_MEM, 0); 91 base = devm_ioremap_resource(&pdev->dev, res); 92 if (IS_ERR(base)) 93 return PTR_ERR(base); 94 95 clk = devm_clk_get(&pdev->dev, NULL); 96 if (IS_ERR(clk)) 97 return PTR_ERR(clk); 98 99 ret = clk_prepare_enable(clk); 100 if (ret) 101 return ret; 102 103 ddata->ops.priv = (unsigned long)ddata; 104 ddata->ops.read = st_rng_read; 105 ddata->ops.name = pdev->name; 106 ddata->base = base; 107 ddata->clk = clk; 108 109 dev_set_drvdata(&pdev->dev, ddata); 110 111 ret = hwrng_register(&ddata->ops); 112 if (ret) { 113 dev_err(&pdev->dev, "Failed to register HW RNG\n"); 114 return ret; 115 } 116 117 dev_info(&pdev->dev, "Successfully registered HW RNG\n"); 118 119 return 0; 120 } 121 122 static int st_rng_remove(struct platform_device *pdev) 123 { 124 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev); 125 126 hwrng_unregister(&ddata->ops); 127 128 clk_disable_unprepare(ddata->clk); 129 130 return 0; 131 } 132 133 static const struct of_device_id st_rng_match[] = { 134 { .compatible = "st,rng" }, 135 {}, 136 }; 137 MODULE_DEVICE_TABLE(of, st_rng_match); 138 139 static struct platform_driver st_rng_driver = { 140 .driver = { 141 .name = "st-hwrandom", 142 .of_match_table = of_match_ptr(st_rng_match), 143 }, 144 .probe = st_rng_probe, 145 .remove = st_rng_remove 146 }; 147 148 module_platform_driver(st_rng_driver); 149 150 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>"); 151 MODULE_LICENSE("GPL v2"); 152