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 if (count < 0) 50 return count; 51 52 return count == bytes ? 0 : -EIO; 53 } 54 55 static int rmem_probe(struct platform_device *pdev) 56 { 57 struct nvmem_config config = { }; 58 struct device *dev = &pdev->dev; 59 struct reserved_mem *mem; 60 struct rmem *priv; 61 62 priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL); 63 if (!priv) 64 return -ENOMEM; 65 priv->dev = dev; 66 67 mem = of_reserved_mem_lookup(dev->of_node); 68 if (!mem) { 69 dev_err(dev, "Failed to lookup reserved memory\n"); 70 return -EINVAL; 71 } 72 priv->mem = mem; 73 74 config.dev = dev; 75 config.priv = priv; 76 config.name = "rmem"; 77 config.id = NVMEM_DEVID_AUTO; 78 config.size = mem->size; 79 config.reg_read = rmem_read; 80 81 return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config)); 82 } 83 84 static const struct of_device_id rmem_match[] = { 85 { .compatible = "nvmem-rmem", }, 86 { /* sentinel */ }, 87 }; 88 MODULE_DEVICE_TABLE(of, rmem_match); 89 90 static struct platform_driver rmem_driver = { 91 .probe = rmem_probe, 92 .driver = { 93 .name = "rmem", 94 .of_match_table = rmem_match, 95 }, 96 }; 97 module_platform_driver(rmem_driver); 98 99 MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>"); 100 MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver"); 101 MODULE_LICENSE("GPL"); 102