1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de> 4 */ 5 6 #include <linux/io.h> 7 #include <linux/module.h> 8 #include <linux/nvmem-provider.h> 9 #include <linux/of_reserved_mem.h> 10 #include <linux/platform_device.h> 11 12 struct rmem { 13 struct device *dev; 14 struct nvmem_device *nvmem; 15 struct reserved_mem *mem; 16 17 phys_addr_t size; 18 }; 19 20 static int rmem_read(void *context, unsigned int offset, 21 void *val, size_t bytes) 22 { 23 struct rmem *priv = context; 24 size_t available = priv->mem->size; 25 loff_t off = offset; 26 void *addr; 27 int count; 28 29 /* 30 * Only map the reserved memory at this point to avoid potential rogue 31 * kernel threads inadvertently modifying it. Based on the current 32 * uses-cases for this driver, the performance hit isn't a concern. 33 * Nor is likely to be, given the nature of the subsystem. Most nvmem 34 * devices operate over slow buses to begin with. 35 * 36 * An alternative would be setting the memory as RO, set_memory_ro(), 37 * but as of Dec 2020 this isn't possible on arm64. 38 */ 39 addr = memremap(priv->mem->base, available, MEMREMAP_WB); 40 if (!addr) { 41 dev_err(priv->dev, "Failed to remap memory region\n"); 42 return -ENOMEM; 43 } 44 45 count = memory_read_from_buffer(val, bytes, &off, addr, available); 46 47 memunmap(addr); 48 49 return count; 50 } 51 52 static int rmem_probe(struct platform_device *pdev) 53 { 54 struct nvmem_config config = { }; 55 struct device *dev = &pdev->dev; 56 struct reserved_mem *mem; 57 struct rmem *priv; 58 59 priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL); 60 if (!priv) 61 return -ENOMEM; 62 priv->dev = dev; 63 64 mem = of_reserved_mem_lookup(dev->of_node); 65 if (!mem) { 66 dev_err(dev, "Failed to lookup reserved memory\n"); 67 return -EINVAL; 68 } 69 priv->mem = mem; 70 71 config.dev = dev; 72 config.priv = priv; 73 config.name = "rmem"; 74 config.size = mem->size; 75 config.reg_read = rmem_read; 76 77 return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config)); 78 } 79 80 static const struct of_device_id rmem_match[] = { 81 { .compatible = "nvmem-rmem", }, 82 { /* sentinel */ }, 83 }; 84 MODULE_DEVICE_TABLE(of, rmem_match); 85 86 static struct platform_driver rmem_driver = { 87 .probe = rmem_probe, 88 .driver = { 89 .name = "rmem", 90 .of_match_table = rmem_match, 91 }, 92 }; 93 module_platform_driver(rmem_driver); 94 95 MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>"); 96 MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver"); 97 MODULE_LICENSE("GPL"); 98