1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * ST Random Number Generator Driver ST's Platforms 4 * 5 * Author: Pankaj Dev: <pankaj.dev@st.com> 6 * Lee Jones <lee.jones@linaro.org> 7 * 8 * Copyright (C) 2015 STMicroelectronics (R&D) Limited 9 */ 10 11 #include <linux/clk.h> 12 #include <linux/delay.h> 13 #include <linux/hw_random.h> 14 #include <linux/io.h> 15 #include <linux/kernel.h> 16 #include <linux/module.h> 17 #include <linux/of.h> 18 #include <linux/platform_device.h> 19 #include <linux/slab.h> 20 21 /* Registers */ 22 #define ST_RNG_STATUS_REG 0x20 23 #define ST_RNG_DATA_REG 0x24 24 25 /* Registers fields */ 26 #define ST_RNG_STATUS_BAD_SEQUENCE BIT(0) 27 #define ST_RNG_STATUS_BAD_ALTERNANCE BIT(1) 28 #define ST_RNG_STATUS_FIFO_FULL BIT(5) 29 30 #define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */ 31 #define ST_RNG_FIFO_DEPTH 4 32 #define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE) 33 34 /* 35 * Samples are documented to be available every 0.667us, so in theory 36 * the 4 sample deep FIFO should take 2.668us to fill. However, during 37 * thorough testing, it became apparent that filling the FIFO actually 38 * takes closer to 12us. We then multiply by 2 in order to account for 39 * the lack of udelay()'s reliability, suggested by Russell King. 40 */ 41 #define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2) 42 43 struct st_rng_data { 44 void __iomem *base; 45 struct clk *clk; 46 struct hwrng ops; 47 }; 48 49 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait) 50 { 51 struct st_rng_data *ddata = (struct st_rng_data *)rng->priv; 52 u32 status; 53 int i; 54 55 /* Wait until FIFO is full - max 4uS*/ 56 for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) { 57 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG); 58 if (status & ST_RNG_STATUS_FIFO_FULL) 59 break; 60 udelay(1); 61 } 62 63 if (i == ST_RNG_FILL_FIFO_TIMEOUT) 64 return 0; 65 66 for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2) 67 *(u16 *)(data + i) = 68 readl_relaxed(ddata->base + ST_RNG_DATA_REG); 69 70 return i; /* No of bytes read */ 71 } 72 73 static int st_rng_probe(struct platform_device *pdev) 74 { 75 struct st_rng_data *ddata; 76 struct clk *clk; 77 void __iomem *base; 78 int ret; 79 80 ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL); 81 if (!ddata) 82 return -ENOMEM; 83 84 base = devm_platform_ioremap_resource(pdev, 0); 85 if (IS_ERR(base)) 86 return PTR_ERR(base); 87 88 clk = devm_clk_get(&pdev->dev, NULL); 89 if (IS_ERR(clk)) 90 return PTR_ERR(clk); 91 92 ret = clk_prepare_enable(clk); 93 if (ret) 94 return ret; 95 96 ddata->ops.priv = (unsigned long)ddata; 97 ddata->ops.read = st_rng_read; 98 ddata->ops.name = pdev->name; 99 ddata->base = base; 100 ddata->clk = clk; 101 102 dev_set_drvdata(&pdev->dev, ddata); 103 104 ret = devm_hwrng_register(&pdev->dev, &ddata->ops); 105 if (ret) { 106 dev_err(&pdev->dev, "Failed to register HW RNG\n"); 107 clk_disable_unprepare(clk); 108 return ret; 109 } 110 111 dev_info(&pdev->dev, "Successfully registered HW RNG\n"); 112 113 return 0; 114 } 115 116 static int st_rng_remove(struct platform_device *pdev) 117 { 118 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev); 119 120 clk_disable_unprepare(ddata->clk); 121 122 return 0; 123 } 124 125 static const struct of_device_id st_rng_match[] __maybe_unused = { 126 { .compatible = "st,rng" }, 127 {}, 128 }; 129 MODULE_DEVICE_TABLE(of, st_rng_match); 130 131 static struct platform_driver st_rng_driver = { 132 .driver = { 133 .name = "st-hwrandom", 134 .of_match_table = of_match_ptr(st_rng_match), 135 }, 136 .probe = st_rng_probe, 137 .remove = st_rng_remove 138 }; 139 140 module_platform_driver(st_rng_driver); 141 142 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>"); 143 MODULE_LICENSE("GPL v2"); 144