How to Validate the plane control capability vsyncDisplayLatency

[akhilbhas]

As per the specification we can see the capability vsynDisplayLatency as

Specifies the display latency of this plane.
Measured in vsync periods, the display latency is measured from
the moment a change is made to plane (e.g. video frame presented)
to the moment it appears on the output display (e.g. panel or HDMI output).

rdk-halif-aidl/planecontrol/current/com/rdk/hal/planecontrol/Capabilities.aidl

Line 101 in 7decb93

* Specifies the display latency of this plane.

We need to identify a method to measure and check if it is as specified in the plane control capability.

[Ulrond]

Hi @akhilbhas,

vsyncDisplayLatency is a vendor-declared capability, not something that VTS can independently measure. It describes the pipeline depth from frame presentation to display output, which is an inherent hardware/firmware characteristic of the SoC's display pipeline.

What VTS can validate:

1. Sanity check the value — verify it is > 0 and within a reasonable range (typically 1–4 vsync periods). A value of 0 or an unreasonably large value would indicate a misconfigured capability.
2. Consistency — verify that getCapabilities() returns the same vsyncDisplayLatency value across multiple calls (the spec states capabilities must not change between calls).
3. Per-plane correctness — verify that different plane types (video vs graphics) may report different latencies, reflecting their actual pipeline depth.

What VTS cannot validate:

Measuring actual display latency requires external instrumentation (e.g., a high-speed camera or photodiode on the display panel, synchronised with the frame presentation timestamp). This is outside the scope of automated VTS — it falls into hardware qualification testing performed by the SoC vendor during platform bring-up.

The vendor is responsible for declaring the correct value based on their platform's display pipeline architecture. VTS trusts this declaration and validates only that it is well-formed and consistent.