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
12struct rmem {
13 struct device *dev;
14 struct nvmem_device *nvmem;
15 struct reserved_mem *mem;
16
17 phys_addr_t size;
18};
19
20static 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(offset: priv->mem->base, size: available, flags: 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(to: val, count: bytes, ppos: &off, from: addr, available);
46
47 memunmap(addr);
48
49 return count;
50}
51
52static 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, size: sizeof(*priv), GFP_KERNEL);
60 if (!priv)
61 return -ENOMEM;
62 priv->dev = dev;
63
64 mem = of_reserved_mem_lookup(np: 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.id = NVMEM_DEVID_AUTO;
75 config.size = mem->size;
76 config.reg_read = rmem_read;
77
78 return PTR_ERR_OR_ZERO(ptr: devm_nvmem_register(dev, cfg: &config));
79}
80
81static const struct of_device_id rmem_match[] = {
82 { .compatible = "nvmem-rmem", },
83 { /* sentinel */ },
84};
85MODULE_DEVICE_TABLE(of, rmem_match);
86
87static struct platform_driver rmem_driver = {
88 .probe = rmem_probe,
89 .driver = {
90 .name = "rmem",
91 .of_match_table = rmem_match,
92 },
93};
94module_platform_driver(rmem_driver);
95
96MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
97MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
98MODULE_LICENSE("GPL");
99

source code of linux/drivers/nvmem/rmem.c