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// SPDX-License-Identifier: MIT
/*
* Copyright © 2021 Intel Corporation
*/
#include <drm/drm_displayid.h>
#include <drm/drm_edid.h>
#include <drm/drm_print.h>
static int validate_displayid(const u8 *displayid, int length, int idx)
{
int i, dispid_length;
u8 csum = 0;
const struct displayid_hdr *base;
base = (const struct displayid_hdr *)&displayid[idx];
DRM_DEBUG_KMS("base revision 0x%x, length %d, %d %d\n",
base->rev, base->bytes, base->prod_id, base->ext_count);
/* +1 for DispID checksum */
dispid_length = sizeof(*base) + base->bytes + 1;
if (dispid_length > length - idx)
return -EINVAL;
for (i = 0; i < dispid_length; i++)
csum += displayid[idx + i];
if (csum) {
DRM_NOTE("DisplayID checksum invalid, remainder is %d\n", csum);
return -EINVAL;
}
return 0;
}
const u8 *drm_find_displayid_extension(const struct edid *edid,
int *length, int *idx,
int *ext_index)
{
const u8 *displayid = drm_find_edid_extension(edid, DISPLAYID_EXT, ext_index);
const struct displayid_hdr *base;
int ret;
if (!displayid)
return NULL;
/* EDID extensions block checksum isn't for us */
*length = EDID_LENGTH - 1;
*idx = 1;
ret = validate_displayid(displayid, *length, *idx);
if (ret)
return NULL;
base = (const struct displayid_hdr *)&displayid[*idx];
*length = *idx + sizeof(*base) + base->bytes;
return displayid;
}
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