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/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
  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 (!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         if (count < 0)
  50                 return count;
  51
  52         return count == bytes ? 0 : -EIO;
  53 }
  54
  55 static int rmem_probe(struct platform_device *pdev)
  56 {
  57         struct nvmem_config config = { };
  58         struct device *dev = &pdev->dev;
  59         struct reserved_mem *mem;
  60         struct rmem *priv;
  61
  62         priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
  63         if (!priv)
  64                 return -ENOMEM;
  65         priv->dev = dev;
  66
  67         mem = of_reserved_mem_lookup(dev->of_node);
  68         if (!mem) {
  69                 dev_err(dev, "Failed to lookup reserved memory\n");
  70                 return -EINVAL;
  71         }
  72         priv->mem = mem;
  73
  74         config.dev = dev;
  75         config.priv = priv;
  76         config.name = "rmem";
  77         config.id = NVMEM_DEVID_AUTO;
  78         config.size = mem->size;
  79         config.reg_read = rmem_read;
  80
  81         return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
  82 }
  83
  84 static const struct of_device_id rmem_match[] = {
  85         { .compatible = "nvmem-rmem", },
  86         { /* sentinel */ },
  87 };
  88 MODULE_DEVICE_TABLE(of, rmem_match);
  89
  90 static struct platform_driver rmem_driver = {
  91         .probe = rmem_probe,
  92         .driver = {
  93                 .name = "rmem",
  94                 .of_match_table = rmem_match,
  95         },
  96 };
  97 module_platform_driver(rmem_driver);
  98
  99 MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
 100 MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
 101 MODULE_LICENSE("GPL");