1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (c) 2024 Broadcom 4 */ 5 6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 7 8 #include <linux/module.h> 9 #include <linux/kernel.h> 10 #include <linux/io.h> 11 #include <linux/delay.h> 12 #include <linux/platform_device.h> 13 #include <linux/random.h> 14 #include <linux/hw_random.h> 15 16 #define HOST_REV_ID 0x00 17 #define HOST_FIFO_DEPTH 0x04 18 #define HOST_FIFO_COUNT 0x08 19 #define HOST_FIFO_THRESHOLD 0x0c 20 #define HOST_FIFO_DATA 0x10 21 22 #define HOST_FIFO_COUNT_MASK 0xffff 23 24 /* Delay range in microseconds */ 25 #define FIFO_DELAY_MIN_US 3 26 #define FIFO_DELAY_MAX_US 7 27 #define FIFO_DELAY_MAX_COUNT 10 28 29 struct bcm74110_priv { 30 void __iomem *base; 31 }; 32 33 static inline int bcm74110_rng_fifo_count(void __iomem *mem) 34 { 35 return readl_relaxed(mem) & HOST_FIFO_COUNT_MASK; 36 } 37 38 static int bcm74110_rng_read(struct hwrng *rng, void *buf, size_t max, 39 bool wait) 40 { 41 struct bcm74110_priv *priv = (struct bcm74110_priv *)rng->priv; 42 void __iomem *fc_addr = priv->base + HOST_FIFO_COUNT; 43 void __iomem *fd_addr = priv->base + HOST_FIFO_DATA; 44 unsigned underrun_count = 0; 45 u32 max_words = max / sizeof(u32); 46 u32 num_words; 47 unsigned i; 48 49 /* 50 * We need to check how many words are available in the RNG FIFO. If 51 * there aren't any, we need to wait for some to become available. 52 */ 53 while ((num_words = bcm74110_rng_fifo_count(fc_addr)) == 0) { 54 if (!wait) 55 return 0; 56 /* 57 * As a precaution, limit how long we wait. If the FIFO doesn't 58 * refill within the allotted time, return 0 (=no data) to the 59 * caller. 60 */ 61 if (likely(underrun_count < FIFO_DELAY_MAX_COUNT)) 62 usleep_range(FIFO_DELAY_MIN_US, FIFO_DELAY_MAX_US); 63 else 64 return 0; 65 underrun_count++; 66 } 67 if (num_words > max_words) 68 num_words = max_words; 69 70 /* Bail early if we run out of random numbers unexpectedly */ 71 for (i = 0; i < num_words && bcm74110_rng_fifo_count(fc_addr) > 0; i++) 72 ((u32 *)buf)[i] = readl_relaxed(fd_addr); 73 74 return i * sizeof(u32); 75 } 76 77 static struct hwrng bcm74110_hwrng = { 78 .read = bcm74110_rng_read, 79 }; 80 81 static int bcm74110_rng_probe(struct platform_device *pdev) 82 { 83 struct device *dev = &pdev->dev; 84 struct bcm74110_priv *priv; 85 int rc; 86 87 priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL); 88 if (!priv) 89 return -ENOMEM; 90 91 bcm74110_hwrng.name = pdev->name; 92 bcm74110_hwrng.priv = (unsigned long)priv; 93 94 priv->base = devm_platform_ioremap_resource(pdev, 0); 95 if (IS_ERR(priv->base)) 96 return PTR_ERR(priv->base); 97 98 rc = devm_hwrng_register(dev, &bcm74110_hwrng); 99 if (rc) 100 dev_err(dev, "hwrng registration failed (%d)\n", rc); 101 else 102 dev_info(dev, "hwrng registered\n"); 103 104 return rc; 105 } 106 107 static const struct of_device_id bcm74110_rng_match[] = { 108 { .compatible = "brcm,bcm74110-rng", }, 109 {}, 110 }; 111 MODULE_DEVICE_TABLE(of, bcm74110_rng_match); 112 113 static struct platform_driver bcm74110_rng_driver = { 114 .driver = { 115 .name = KBUILD_MODNAME, 116 .of_match_table = bcm74110_rng_match, 117 }, 118 .probe = bcm74110_rng_probe, 119 }; 120 module_platform_driver(bcm74110_rng_driver); 121 122 MODULE_AUTHOR("Markus Mayer <mmayer@broadcom.com>"); 123 MODULE_DESCRIPTION("BCM 74110 Random Number Generator (RNG) driver"); 124 MODULE_LICENSE("GPL v2"); 125