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 resource *res; 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 res = platform_get_resource(pdev, IORESOURCE_MEM, 0); 85 base = devm_ioremap_resource(&pdev->dev, res); 86 if (IS_ERR(base)) 87 return PTR_ERR(base); 88 89 clk = devm_clk_get(&pdev->dev, NULL); 90 if (IS_ERR(clk)) 91 return PTR_ERR(clk); 92 93 ret = clk_prepare_enable(clk); 94 if (ret) 95 return ret; 96 97 ddata->ops.priv = (unsigned long)ddata; 98 ddata->ops.read = st_rng_read; 99 ddata->ops.name = pdev->name; 100 ddata->base = base; 101 ddata->clk = clk; 102 103 dev_set_drvdata(&pdev->dev, ddata); 104 105 ret = hwrng_register(&ddata->ops); 106 if (ret) { 107 dev_err(&pdev->dev, "Failed to register HW RNG\n"); 108 clk_disable_unprepare(clk); 109 return ret; 110 } 111 112 dev_info(&pdev->dev, "Successfully registered HW RNG\n"); 113 114 return 0; 115 } 116 117 static int st_rng_remove(struct platform_device *pdev) 118 { 119 struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev); 120 121 hwrng_unregister(&ddata->ops); 122 123 clk_disable_unprepare(ddata->clk); 124 125 return 0; 126 } 127 128 static const struct of_device_id st_rng_match[] = { 129 { .compatible = "st,rng" }, 130 {}, 131 }; 132 MODULE_DEVICE_TABLE(of, st_rng_match); 133 134 static struct platform_driver st_rng_driver = { 135 .driver = { 136 .name = "st-hwrandom", 137 .of_match_table = of_match_ptr(st_rng_match), 138 }, 139 .probe = st_rng_probe, 140 .remove = st_rng_remove 141 }; 142 143 module_platform_driver(st_rng_driver); 144 145 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>"); 146 MODULE_LICENSE("GPL v2"); 147