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(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
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, 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.id = NVMEM_DEVID_AUTO;
75	config.size = mem->size;
76	config.reg_read = rmem_read;
77
78	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &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