drivers/nvmem/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
  14 struct rmem {
  15         struct device *dev;
  16         struct nvmem_device *nvmem;
  17         struct reserved_mem *mem;
  18 };
  19
  20 struct rmem_match_data {
  21         int (*checksum)(struct rmem *priv);
  22 };
  23
  24 struct __packed rmem_eyeq5_header {
  25         u32 magic;
  26         u32 version;
  27         u32 size;
  28 };
  29
  30 #define RMEM_EYEQ5_MAGIC        ((u32)0xDABBAD00)
  31
  32 static 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
  64 static 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
 119 static 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
 156 static const struct rmem_match_data rmem_eyeq5_match_data = {
 157         .checksum = rmem_eyeq5_checksum,
 158 };
 159
 160 static 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 };
 165 MODULE_DEVICE_TABLE(of, rmem_match);
 166
 167 static struct platform_driver rmem_driver = {
 168         .probe = rmem_probe,
 169         .driver = {
 170                 .name = "rmem",
 171                 .of_match_table = rmem_match,
 172         },
 173 };
 174 module_platform_driver(rmem_driver);
 175
 176 MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
 177 MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
 178 MODULE_LICENSE("GPL");