drivers/misc/eeprom/sunxi_sid.c

   1 /*
   2  * Copyright (c) 2013 Oliver Schinagl <oliver@schinagl.nl>
   3  * http://www.linux-sunxi.org
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * This driver exposes the Allwinner security ID, efuses exported in byte-
  16  * sized chunks.
  17  */
  18
  19 #include <linux/compiler.h>
  20 #include <linux/device.h>
  21 #include <linux/err.h>
  22 #include <linux/export.h>
  23 #include <linux/fs.h>
  24 #include <linux/io.h>
  25 #include <linux/kernel.h>
  26 #include <linux/kobject.h>
  27 #include <linux/module.h>
  28 #include <linux/of_device.h>
  29 #include <linux/platform_device.h>
  30 #include <linux/random.h>
  31 #include <linux/slab.h>
  32 #include <linux/stat.h>
  33 #include <linux/sysfs.h>
  34 #include <linux/types.h>
  35
  36 #define DRV_NAME "sunxi-sid"
  37
  38 struct sunxi_sid_data {
  39         void __iomem *reg_base;
  40         unsigned int keysize;
  41 };
  42
  43 /* We read the entire key, due to a 32 bit read alignment requirement. Since we
  44  * want to return the requested byte, this results in somewhat slower code and
  45  * uses 4 times more reads as needed but keeps code simpler. Since the SID is
  46  * only very rarely probed, this is not really an issue.
  47  */
  48 static u8 sunxi_sid_read_byte(const struct sunxi_sid_data *sid_data,
  49                               const unsigned int offset)
  50 {
  51         u32 sid_key;
  52
  53         if (offset >= sid_data->keysize)
  54                 return 0;
  55
  56         sid_key = ioread32be(sid_data->reg_base + round_down(offset, 4));
  57         sid_key >>= (offset % 4) * 8;
  58
  59         return sid_key; /* Only return the last byte */
  60 }
  61
  62 static ssize_t sid_read(struct file *fd, struct kobject *kobj,
  63                         struct bin_attribute *attr, char *buf,
  64                         loff_t pos, size_t size)
  65 {
  66         struct platform_device *pdev;
  67         struct sunxi_sid_data *sid_data;
  68         int i;
  69
  70         pdev = to_platform_device(kobj_to_dev(kobj));
  71         sid_data = platform_get_drvdata(pdev);
  72
  73         if (pos < 0 || pos >= sid_data->keysize)
  74                 return 0;
  75         if (size > sid_data->keysize - pos)
  76                 size = sid_data->keysize - pos;
  77
  78         for (i = 0; i < size; i++)
  79                 buf[i] = sunxi_sid_read_byte(sid_data, pos + i);
  80
  81         return i;
  82 }
  83
  84 static struct bin_attribute sid_bin_attr = {
  85         .attr = { .name = "eeprom", .mode = S_IRUGO, },
  86         .read = sid_read,
  87 };
  88
  89 static int sunxi_sid_remove(struct platform_device *pdev)
  90 {
  91         device_remove_bin_file(&pdev->dev, &sid_bin_attr);
  92         dev_dbg(&pdev->dev, "driver unloaded\n");
  93
  94         return 0;
  95 }
  96
  97 static const struct of_device_id sunxi_sid_of_match[] = {
  98         { .compatible = "allwinner,sun4i-a10-sid", .data = (void *)16},
  99         { .compatible = "allwinner,sun7i-a20-sid", .data = (void *)512},
 100         {/* sentinel */},
 101 };
 102 MODULE_DEVICE_TABLE(of, sunxi_sid_of_match);
 103
 104 static int sunxi_sid_probe(struct platform_device *pdev)
 105 {
 106         struct sunxi_sid_data *sid_data;
 107         struct resource *res;
 108         const struct of_device_id *of_dev_id;
 109         u8 *entropy;
 110         unsigned int i;
 111
 112         sid_data = devm_kzalloc(&pdev->dev, sizeof(struct sunxi_sid_data),
 113                                 GFP_KERNEL);
 114         if (!sid_data)
 115                 return -ENOMEM;
 116
 117         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 118         sid_data->reg_base = devm_ioremap_resource(&pdev->dev, res);
 119         if (IS_ERR(sid_data->reg_base))
 120                 return PTR_ERR(sid_data->reg_base);
 121
 122         of_dev_id = of_match_device(sunxi_sid_of_match, &pdev->dev);
 123         if (!of_dev_id)
 124                 return -ENODEV;
 125         sid_data->keysize = (int)of_dev_id->data;
 126
 127         platform_set_drvdata(pdev, sid_data);
 128
 129         sid_bin_attr.size = sid_data->keysize;
 130         if (device_create_bin_file(&pdev->dev, &sid_bin_attr))
 131                 return -ENODEV;
 132
 133         entropy = kzalloc(sizeof(u8) * sid_data->keysize, GFP_KERNEL);
 134         for (i = 0; i < sid_data->keysize; i++)
 135                 entropy[i] = sunxi_sid_read_byte(sid_data, i);
 136         add_device_randomness(entropy, sid_data->keysize);
 137         kfree(entropy);
 138
 139         dev_dbg(&pdev->dev, "loaded\n");
 140
 141         return 0;
 142 }
 143
 144 static struct platform_driver sunxi_sid_driver = {
 145         .probe = sunxi_sid_probe,
 146         .remove = sunxi_sid_remove,
 147         .driver = {
 148                 .name = DRV_NAME,
 149                 .of_match_table = sunxi_sid_of_match,
 150         },
 151 };
 152 module_platform_driver(sunxi_sid_driver);
 153
 154 MODULE_AUTHOR("Oliver Schinagl <oliver@schinagl.nl>");
 155 MODULE_DESCRIPTION("Allwinner sunxi security id driver");
 156 MODULE_LICENSE("GPL");