drivers/firmware/efi/rci2-table.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Export Runtime Configuration Interface Table Version 2 (RCI2)
   4  * to sysfs
   5  *
   6  * Copyright (C) 2019 Dell Inc
   7  * by Narendra K <Narendra.K@dell.com>
   8  *
   9  * System firmware advertises the address of the RCI2 Table via
  10  * an EFI Configuration Table entry. This code retrieves the RCI2
  11  * table from the address and exports it to sysfs as a binary
  12  * attribute 'rci2' under /sys/firmware/efi/tables directory.
  13  */
  14
  15 #include <linux/kobject.h>
  16 #include <linux/device.h>
  17 #include <linux/sysfs.h>
  18 #include <linux/efi.h>
  19 #include <linux/types.h>
  20 #include <linux/io.h>
  21
  22 #define RCI_SIGNATURE   "_RC_"
  23
  24 struct rci2_table_global_hdr {
  25         u16 type;
  26         u16 resvd0;
  27         u16 hdr_len;
  28         u8 rci2_sig[4];
  29         u16 resvd1;
  30         u32 resvd2;
  31         u32 resvd3;
  32         u8 major_rev;
  33         u8 minor_rev;
  34         u16 num_of_structs;
  35         u32 rci2_len;
  36         u16 rci2_chksum;
  37 } __packed;
  38
  39 static u8 *rci2_base;
  40 static u32 rci2_table_len;
  41 unsigned long rci2_table_phys __ro_after_init = EFI_INVALID_TABLE_ADDR;
  42
  43 static ssize_t raw_table_read(struct file *file, struct kobject *kobj,
  44                               struct bin_attribute *attr, char *buf,
  45                               loff_t pos, size_t count)
  46 {
  47         memcpy(buf, attr->private + pos, count);
  48         return count;
  49 }
  50
  51 static BIN_ATTR(rci2, S_IRUSR, raw_table_read, NULL, 0);
  52
  53 static u16 checksum(void)
  54 {
  55         u8 len_is_odd = rci2_table_len % 2;
  56         u32 chksum_len = rci2_table_len;
  57         u16 *base = (u16 *)rci2_base;
  58         u8 buf[2] = {0};
  59         u32 offset = 0;
  60         u16 chksum = 0;
  61
  62         if (len_is_odd)
  63                 chksum_len -= 1;
  64
  65         while (offset < chksum_len) {
  66                 chksum += *base;
  67                 offset += 2;
  68                 base++;
  69         }
  70
  71         if (len_is_odd) {
  72                 buf[0] = *(u8 *)base;
  73                 chksum += *(u16 *)(buf);
  74         }
  75
  76         return chksum;
  77 }
  78
  79 static int __init efi_rci2_sysfs_init(void)
  80 {
  81         struct kobject *tables_kobj;
  82         int ret = -ENOMEM;
  83
  84         rci2_base = memremap(rci2_table_phys,
  85                              sizeof(struct rci2_table_global_hdr),
  86                              MEMREMAP_WB);
  87         if (!rci2_base) {
  88                 pr_debug("RCI2 table init failed - could not map RCI2 table\n");
  89                 goto err;
  90         }
  91
  92         if (strncmp(rci2_base +
  93                     offsetof(struct rci2_table_global_hdr, rci2_sig),
  94                     RCI_SIGNATURE, 4)) {
  95                 pr_debug("RCI2 table init failed - incorrect signature\n");
  96                 ret = -ENODEV;
  97                 goto err_unmap;
  98         }
  99
 100         rci2_table_len = *(u32 *)(rci2_base +
 101                                   offsetof(struct rci2_table_global_hdr,
 102                                   rci2_len));
 103
 104         memunmap(rci2_base);
 105
 106         if (!rci2_table_len) {
 107                 pr_debug("RCI2 table init failed - incorrect table length\n");
 108                 goto err;
 109         }
 110
 111         rci2_base = memremap(rci2_table_phys, rci2_table_len, MEMREMAP_WB);
 112         if (!rci2_base) {
 113                 pr_debug("RCI2 table - could not map RCI2 table\n");
 114                 goto err;
 115         }
 116
 117         if (checksum() != 0) {
 118                 pr_debug("RCI2 table - incorrect checksum\n");
 119                 ret = -ENODEV;
 120                 goto err_unmap;
 121         }
 122
 123         tables_kobj = kobject_create_and_add("tables", efi_kobj);
 124         if (!tables_kobj) {
 125                 pr_debug("RCI2 table - tables_kobj creation failed\n");
 126                 goto err_unmap;
 127         }
 128
 129         bin_attr_rci2.size = rci2_table_len;
 130         bin_attr_rci2.private = rci2_base;
 131         ret = sysfs_create_bin_file(tables_kobj, &bin_attr_rci2);
 132         if (ret != 0) {
 133                 pr_debug("RCI2 table - rci2 sysfs bin file creation failed\n");
 134                 kobject_del(tables_kobj);
 135                 kobject_put(tables_kobj);
 136                 goto err_unmap;
 137         }
 138
 139         return 0;
 140
 141  err_unmap:
 142         memunmap(rci2_base);
 143  err:
 144         pr_debug("RCI2 table - sysfs initialization failed\n");
 145         return ret;
 146 }
 147 late_initcall(efi_rci2_sysfs_init);