drm/amd/display: Test AUX transfer paths

[WHAT]
Add KUnit tests for the AUX paths of dm_helper_dmub_aux_transfer_sync(),
dm_helpers_read_mccs_caps() and dm_helpers_mccs_vcp_set(). Only their
early returns and the plain I2C branch were covered before.

[HOW]
dm_helper_dmub_aux_transfer_sync() is called with HPD connected so it
forwards the payload to the DMUB transfer. dc->link_count is zero, so
the async transfer is rejected and the engine-acquire error is
reported.

Both MCCS helpers pick their DDC adapter from link->aux_mode. Add a
fake AUX channel that ACKs every I2C-over-AUX transaction and counts
the sized writes, then route the shared MCCS fixture through it. The
VCP set completes on the first write. The VCP request gets an empty
reply, so every attempt is retried and the request finally fails.

Assisted-by: Copilot:Claude-Opus-5
Reviewed-by: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

0 files changed, 0 insertions, 0 deletions