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 BIN_ATTR_SIMPLE_ADMIN_RO(rci2);
  44
  45 static u16 checksum(void)
  46 {
  47         u8 len_is_odd = rci2_table_len % 2;
  48         u32 chksum_len = rci2_table_len;
  49         u16 *base = (u16 *)rci2_base;
  50         u8 buf[2] = {0};
  51         u32 offset = 0;
  52         u16 chksum = 0;
  53
  54         if (len_is_odd)
  55                 chksum_len -= 1;
  56
  57         while (offset < chksum_len) {
  58                 chksum += *base;
  59                 offset += 2;
  60                 base++;
  61         }
  62
  63         if (len_is_odd) {
  64                 buf[0] = *(u8 *)base;
  65                 chksum += *(u16 *)(buf);
  66         }
  67
  68         return chksum;
  69 }
  70
  71 static int __init efi_rci2_sysfs_init(void)
  72 {
  73         struct kobject *tables_kobj;
  74         int ret = -ENOMEM;
  75
  76         if (rci2_table_phys == EFI_INVALID_TABLE_ADDR)
  77                 return 0;
  78
  79         rci2_base = memremap(rci2_table_phys,
  80                              sizeof(struct rci2_table_global_hdr),
  81                              MEMREMAP_WB);
  82         if (!rci2_base) {
  83                 pr_debug("RCI2 table init failed - could not map RCI2 table\n");
  84                 goto err;
  85         }
  86
  87         if (strncmp(rci2_base +
  88                     offsetof(struct rci2_table_global_hdr, rci2_sig),
  89                     RCI_SIGNATURE, 4)) {
  90                 pr_debug("RCI2 table init failed - incorrect signature\n");
  91                 ret = -ENODEV;
  92                 goto err_unmap;
  93         }
  94
  95         rci2_table_len = *(u32 *)(rci2_base +
  96                                   offsetof(struct rci2_table_global_hdr,
  97                                   rci2_len));
  98
  99         memunmap(rci2_base);
 100
 101         if (!rci2_table_len) {
 102                 pr_debug("RCI2 table init failed - incorrect table length\n");
 103                 goto err;
 104         }
 105
 106         rci2_base = memremap(rci2_table_phys, rci2_table_len, MEMREMAP_WB);
 107         if (!rci2_base) {
 108                 pr_debug("RCI2 table - could not map RCI2 table\n");
 109                 goto err;
 110         }
 111
 112         if (checksum() != 0) {
 113                 pr_debug("RCI2 table - incorrect checksum\n");
 114                 ret = -ENODEV;
 115                 goto err_unmap;
 116         }
 117
 118         tables_kobj = kobject_create_and_add("tables", efi_kobj);
 119         if (!tables_kobj) {
 120                 pr_debug("RCI2 table - tables_kobj creation failed\n");
 121                 goto err_unmap;
 122         }
 123
 124         bin_attr_rci2.size = rci2_table_len;
 125         bin_attr_rci2.private = rci2_base;
 126         ret = sysfs_create_bin_file(tables_kobj, &bin_attr_rci2);
 127         if (ret != 0) {
 128                 pr_debug("RCI2 table - rci2 sysfs bin file creation failed\n");
 129                 kobject_del(tables_kobj);
 130                 kobject_put(tables_kobj);
 131                 goto err_unmap;
 132         }
 133
 134         return 0;
 135
 136  err_unmap:
 137         memunmap(rci2_base);
 138  err:
 139         pr_debug("RCI2 table - sysfs initialization failed\n");
 140         return ret;
 141 }
 142 late_initcall(efi_rci2_sysfs_init);