rmem.c

  1// SPDX-License-Identifier: GPL-2.0+
  2/*
  3 * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
  4 */
  5
  6#include <linux/crc32.h>
  7#include <linux/io.h>
  8#include <linux/module.h>
  9#include <linux/nvmem-provider.h>
 10#include <linux/of_reserved_mem.h>
 11#include <linux/platform_device.h>
 12#include <linux/slab.h>
 13
 14struct rmem {
 15	struct device *dev;
 16	struct nvmem_device *nvmem;
 17	struct reserved_mem *mem;
 18};
 19
 20struct rmem_match_data {
 21	int (*checksum)(struct rmem *priv);
 22};
 23
 24struct __packed rmem_eyeq5_header {
 25	u32 magic;
 26	u32 version;
 27	u32 size;
 28};
 29
 30#define RMEM_EYEQ5_MAGIC	((u32)0xDABBAD00)
 31
 32static int rmem_read(void *context, unsigned int offset,
 33		     void *val, size_t bytes)
 34{
 35	struct rmem *priv = context;
 36	void *addr;
 37
 38	if ((phys_addr_t)offset + bytes > priv->mem->size)
 39		return -EIO;
 40
 41	/*
 42	 * Only map the reserved memory at this point to avoid potential rogue
 43	 * kernel threads inadvertently modifying it. Based on the current
 44	 * uses-cases for this driver, the performance hit isn't a concern.
 45	 * Nor is likely to be, given the nature of the subsystem. Most nvmem
 46	 * devices operate over slow buses to begin with.
 47	 *
 48	 * An alternative would be setting the memory as RO, set_memory_ro(),
 49	 * but as of Dec 2020 this isn't possible on arm64.
 50	 */
 51	addr = memremap(priv->mem->base, priv->mem->size, MEMREMAP_WB);
 52	if (!addr) {
 53		dev_err(priv->dev, "Failed to remap memory region\n");
 54		return -ENOMEM;
 55	}
 56
 57	memcpy(val, addr + offset, bytes);
 58
 59	memunmap(addr);
 60
 61	return 0;
 62}
 63
 64static int rmem_eyeq5_checksum(struct rmem *priv)
 65{
 66	void *buf __free(kfree) = NULL;
 67	struct rmem_eyeq5_header header;
 68	u32 computed_crc, *target_crc;
 69	size_t data_size;
 70	int ret;
 71
 72	ret = rmem_read(priv, 0, &header, sizeof(header));
 73	if (ret)
 74		return ret;
 75
 76	if (header.magic != RMEM_EYEQ5_MAGIC)
 77		return -EINVAL;
 78
 79	/*
 80	 * Avoid massive kmalloc() if header read is invalid;
 81	 * the check would be done by the next rmem_read() anyway.
 82	 */
 83	if (header.size > priv->mem->size)
 84		return -EINVAL;
 85
 86	/*
 87	 *           0 +-------------------+
 88	 *             | Header (12 bytes) | \
 89	 *             +-------------------+ |
 90	 *             |                   | | data to be CRCed
 91	 *             |        ...        | |
 92	 *             |                   | /
 93	 *   data_size +-------------------+
 94	 *             |   CRC (4 bytes)   |
 95	 * header.size +-------------------+
 96	 */
 97
 98	buf = kmalloc(header.size, GFP_KERNEL);
 99	if (!buf)
100		return -ENOMEM;
101
102	ret = rmem_read(priv, 0, buf, header.size);
103	if (ret)
104		return ret;
105
106	data_size = header.size - sizeof(*target_crc);
107	target_crc = buf + data_size;
108	computed_crc = crc32(U32_MAX, buf, data_size) ^ U32_MAX;
109
110	if (computed_crc == *target_crc)
111		return 0;
112
113	dev_err(priv->dev,
114		"checksum failed: computed %#x, expected %#x, header (%#x, %#x, %#x)\n",
115		computed_crc, *target_crc, header.magic, header.version, header.size);
116	return -EINVAL;
117}
118
119static int rmem_probe(struct platform_device *pdev)
120{
121	struct nvmem_config config = { };
122	struct device *dev = &pdev->dev;
123	const struct rmem_match_data *match_data = device_get_match_data(dev);
124	struct reserved_mem *mem;
125	struct rmem *priv;
126
127	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
128	if (!priv)
129		return -ENOMEM;
130	priv->dev = dev;
131
132	mem = of_reserved_mem_lookup(dev->of_node);
133	if (!mem) {
134		dev_err(dev, "Failed to lookup reserved memory\n");
135		return -EINVAL;
136	}
137	priv->mem = mem;
138
139	config.dev = dev;
140	config.priv = priv;
141	config.name = "rmem";
142	config.id = NVMEM_DEVID_AUTO;
143	config.size = mem->size;
144	config.reg_read = rmem_read;
145
146	if (match_data && match_data->checksum) {
147		int ret = match_data->checksum(priv);
148
149		if (ret)
150			return ret;
151	}
152
153	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
154}
155
156static const struct rmem_match_data rmem_eyeq5_match_data = {
157	.checksum = rmem_eyeq5_checksum,
158};
159
160static const struct of_device_id rmem_match[] = {
161	{ .compatible = "mobileye,eyeq5-bootloader-config", .data = &rmem_eyeq5_match_data },
162	{ .compatible = "nvmem-rmem", },
163	{ /* sentinel */ },
164};
165MODULE_DEVICE_TABLE(of, rmem_match);
166
167static struct platform_driver rmem_driver = {
168	.probe = rmem_probe,
169	.driver = {
170		.name = "rmem",
171		.of_match_table = rmem_match,
172	},
173};
174module_platform_driver(rmem_driver);
175
176MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
177MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
178MODULE_LICENSE("GPL");