[Bug 80683] New: EDID valid check ignores errors in CEA blocks

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=80683

          Priority: medium
            Bug ID: 80683
          Assignee: dri-devel@lists.freedesktop.org
           Summary: EDID valid check ignores errors in CEA blocks
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: stefan.bruens@rwth-aachen.de
          Hardware: Other
            Status: NEW
           Version: DRI CVS
         Component: DRM/other
           Product: DRI

in linux/drivers/gpu/drm/drm_edid.c:

bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid)
{
...
        if (csum) {
                if (print_bad_edid) {
                        DRM_ERROR("EDID checksum is invalid, remainder is
%d\n", csum);
                }

                /* allow CEA to slide through, switches mangle this */
                if (raw_edid[0] != 0x02)
                        goto bad;
        }
...
        return true;
---

i.e. CEA blocks are always reported as valid.

This occurs frequently for me with a Radeon 7750 and a Dell U2713HM connected
via DisplayPort, the I2C-over-AUX seems to be buggy and swallows single bytes.

If I change the "return true;" to "return !csum;" bad transfers are retried.

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