drm: Add edid_corrupt flag for Displayport Link CTS 4.2.2.6

drm: Add edid_corrupt flag for Displayport Link CTS 4.2.2.6

Displayport compliance test 4.2.2.6 requires that a source device be capable of
detecting a corrupt EDID. The test specification states that the sink device
sets up the EDID with an invalid checksum. To do this, the sink sets up an
invalid EDID header, expecting the source device to generate the checksum and
compare it to the value stored in the last byte of the block data.

Unfortunately, the DRM EDID reading and parsing functions are actually too good
in this case; the header is fixed before the checksum is computed and thus the
test never sees the invalid checksum. This results in a failure to pass the
compliance test.

To correct this issue, when the EDID code detects that the header is invalid,
a flag is set to indicate that the EDID is corrupted. In this case, it sets
edid_corrupt flag and continues with its fix-up code. This flag is also set in
the case of a more seriously damaged header (fixup score less than the
threshold). For consistency, the edid_corrupt flag is also set when the
checksum is invalid as well.

V2:
- Removed the static bool global
- Added a bool to the drm_connector struct to reaplce the static one for
  holding the status of raw edid header corruption detection
- Modified the function signature of the is_valid function to take an
  additional parameter to store the corruption detected value
- Fixed the other callers of the above is_valid function
V3:
- Updated the commit message to be more clear about what and why this
  patch does what it does.
- Added comment in code to clarify the operations there
- Removed compliance variable and check_link_status update; those
  have been moved to a later patch
- Removed variable assignment from the bottom of the test handler
V4:
- Removed i915 tag from subject line as the patch is not i915-specific
V5:
- Moved code causing a compilation error to this patch where the variable
  is actually declared
- Maintained blank lines / spacing so as to not contaminate the patch
V6:
- Removed extra debug messages
- Added documentation to for the added parameter on drm_edid_block_valid
- Fixed more whitespace issues in check_link_status
- Added a clear of the header_corrupt flag to the end of the test handler
  in intel_dp.c
- Changed the usage of the new function prototype in several places to use
  NULL where it is not needed by compliance testing
V7:
- Updated to account for long_pulse flag propagation
V8:
- Removed clearing of header_corrupt flag from the test handler in intel_dp.c
- Added clearing of header_corrupt flag in the drm_edid_block_valid function
V9:
- Renamed header_corrupt flag to edid_corrupt to more accurately reflect its
  value and purpose
- Updated commit message
V10:
- Updated for versioning and patch swizzle
- Revised the title to more accurately reflect the nature and contents of
  the patch
- Fixed formatting/whitespace problems
- Added set flag when computed checksum is invalid

Signed-off-by: Todd Previte <tprevite@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>