GitLab

This CL changes the fallback strategy in ConfigureDisplaysTask to submit
requests individually when an atomic modeset test fails. More
particularly, it groups displays by the physical connectors they are
attached to and submit these request groups for atomic modesetting.

For example, if the request {internal display, MST1-1, MST1-2, HDMI}
fails as a whole, the next configuration attempt would repeatedly try
each of the following groups until a modeset succeeds: {internal
display}, {MST1-1, MST1-2} and {HDMI}. When a request group fails
modeset, the request with the highest bandwidth requirement is
downgraded first.

Finally, if any of the request groups exhausts all its alternative
modes, the entire configuration attempt terminates and signals back an
ERROR status.

In addition, this CL adds extensive testing for multiple display
configurations, including multiple MST hubs, nested MST structures,
MST and non-MST (i.e. independent) external displays, bad MST hubs, and
configurations with no internal displays, such as a Chromebox.

Bug: b:176819129, b:177356832
Test: display_unittests && ozone_unittests
Change-Id: Iac2b7f0330a74396c72f8d3867552dde593800e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2621674
Commit-Queue: Gil Dekel <gildekel@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Reviewed-by: Gil Dekel <gildekel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846418}