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
rmem_read(void * context,unsigned int offset,void * val,size_t bytes)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 (IS_ERR(addr)) {
41 dev_err(priv->dev, "Failed to remap memory region\n");
42 return PTR_ERR(addr);
43 }
44
45 count = memory_read_from_buffer(val, bytes, &off, addr, available);
46
47 memunmap(addr);
48
49 return count;
50 }
51
rmem_probe(struct platform_device * pdev)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