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