drivers/gpu/drm/drm_displayid.c

   1 // SPDX-License-Identifier: MIT
   2 /*
   3  * Copyright © 2021 Intel Corporation
   4  */
   5
   6 #include <drm/drm_displayid.h>
   7 #include <drm/drm_edid.h>
   8 #include <drm/drm_print.h>
   9
  10 static const struct displayid_header *
  11 displayid_get_header(const u8 *displayid, int length, int index)
  12 {
  13         const struct displayid_header *base;
  14
  15         if (sizeof(*base) > length - index)
  16                 return ERR_PTR(-EINVAL);
  17
  18         base = (const struct displayid_header *)&displayid[index];
  19
  20         return base;
  21 }
  22
  23 static const struct displayid_header *
  24 validate_displayid(const u8 *displayid, int length, int idx)
  25 {
  26         int i, dispid_length;
  27         u8 csum = 0;
  28         const struct displayid_header *base;
  29
  30         base = displayid_get_header(displayid, length, idx);
  31         if (IS_ERR(base))
  32                 return base;
  33
  34         DRM_DEBUG_KMS("base revision 0x%x, length %d, %d %d\n",
  35                       base->rev, base->bytes, base->prod_id, base->ext_count);
  36
  37         /* +1 for DispID checksum */
  38         dispid_length = sizeof(*base) + base->bytes + 1;
  39         if (dispid_length > length - idx)
  40                 return ERR_PTR(-EINVAL);
  41
  42         for (i = 0; i < dispid_length; i++)
  43                 csum += displayid[idx + i];
  44         if (csum) {
  45                 DRM_NOTE("DisplayID checksum invalid, remainder is %d\n", csum);
  46                 return ERR_PTR(-EINVAL);
  47         }
  48
  49         return base;
  50 }
  51
  52 static const u8 *drm_find_displayid_extension(const struct drm_edid *drm_edid,
  53                                               int *length, int *idx,
  54                                               int *ext_index)
  55 {
  56         const u8 *displayid = drm_find_edid_extension(drm_edid, DISPLAYID_EXT, ext_index);
  57         const struct displayid_header *base;
  58
  59         if (!displayid)
  60                 return NULL;
  61
  62         /* EDID extensions block checksum isn't for us */
  63         *length = EDID_LENGTH - 1;
  64         *idx = 1;
  65
  66         base = validate_displayid(displayid, *length, *idx);
  67         if (IS_ERR(base))
  68                 return NULL;
  69
  70         *length = *idx + sizeof(*base) + base->bytes;
  71
  72         return displayid;
  73 }
  74
  75 void displayid_iter_edid_begin(const struct drm_edid *drm_edid,
  76                                struct displayid_iter *iter)
  77 {
  78         memset(iter, 0, sizeof(*iter));
  79
  80         iter->drm_edid = drm_edid;
  81 }
  82
  83 static const struct displayid_block *
  84 displayid_iter_block(const struct displayid_iter *iter)
  85 {
  86         const struct displayid_block *block;
  87
  88         if (!iter->section)
  89                 return NULL;
  90
  91         block = (const struct displayid_block *)&iter->section[iter->idx];
  92
  93         if (iter->idx + sizeof(*block) <= iter->length &&
  94             iter->idx + sizeof(*block) + block->num_bytes <= iter->length)
  95                 return block;
  96
  97         return NULL;
  98 }
  99
 100 const struct displayid_block *
 101 __displayid_iter_next(struct displayid_iter *iter)
 102 {
 103         const struct displayid_block *block;
 104
 105         if (!iter->drm_edid)
 106                 return NULL;
 107
 108         if (iter->section) {
 109                 /* current block should always be valid */
 110                 block = displayid_iter_block(iter);
 111                 if (WARN_ON(!block)) {
 112                         iter->section = NULL;
 113                         iter->drm_edid = NULL;
 114                         return NULL;
 115                 }
 116
 117                 /* next block in section */
 118                 iter->idx += sizeof(*block) + block->num_bytes;
 119
 120                 block = displayid_iter_block(iter);
 121                 if (block)
 122                         return block;
 123         }
 124
 125         for (;;) {
 126                 /* The first section we encounter is the base section */
 127                 bool base_section = !iter->section;
 128
 129                 iter->section = drm_find_displayid_extension(iter->drm_edid,
 130                                                              &iter->length,
 131                                                              &iter->idx,
 132                                                              &iter->ext_index);
 133                 if (!iter->section) {
 134                         iter->drm_edid = NULL;
 135                         return NULL;
 136                 }
 137
 138                 /* Save the structure version and primary use case. */
 139                 if (base_section) {
 140                         const struct displayid_header *base;
 141
 142                         base = displayid_get_header(iter->section, iter->length,
 143                                                     iter->idx);
 144                         if (!IS_ERR(base)) {
 145                                 iter->version = base->rev;
 146                                 iter->primary_use = base->prod_id;
 147                         }
 148                 }
 149
 150                 iter->idx += sizeof(struct displayid_header);
 151
 152                 block = displayid_iter_block(iter);
 153                 if (block)
 154                         return block;
 155         }
 156 }
 157
 158 void displayid_iter_end(struct displayid_iter *iter)
 159 {
 160         memset(iter, 0, sizeof(*iter));
 161 }
 162
 163 /* DisplayID Structure Version/Revision from the Base Section. */
 164 u8 displayid_version(const struct displayid_iter *iter)
 165 {
 166         return iter->version;
 167 }
 168
 169 /*
 170  * DisplayID Primary Use Case (2.0+) or Product Type Identifier (1.0-1.3) from
 171  * the Base Section.
 172  */
 173 u8 displayid_primary_use(const struct displayid_iter *iter)
 174 {
 175         return iter->primary_use;
 176 }