ChromeOS Compatible - Displays Specification v1.0

Version: 1.0.1
Last updated: 2024-02-01

Legend

Product Verb Development Action
"MUST" Mandatory product requirement
"SHOULD" Optional recommendation
"MAY" Nice to have

Requirements Scope

This document defines the requirements that ChromeOS Compatible displays meet. This specification should not be used for WWCB products, or a product designed and certified together with a Chromebook.

Display Types

This document covers external displays that connect via HDMI, DisplayPort, or USB Type-C. This specification does not cover displays with embedded USB ports or embedded MST hubs.

Hardware and Visual Design

Visual Design

  • Ports SHOULD be labeled consistently with the applicable industry-standard logos
  • Logos SHOULD comply with standards-appropriate marketing guidelines for logo usage
    • DisplayLink/Silicon Motion requirements/capabilities clearly silkscreened on unit
    • Thunderbolt requirements/capabilities clearly silkscreened on unit

Connectivity

  • The display SHOULD include at least one video cable in the box
  • The display MAY include any additional number of additional cables in the box
  • Included cable(s) MUST match the version of the connectivity standard supported by the display
    • For example, if the display supports HDMI 2.1, the included cable MUST be an HDMI 2.1 cable
  • All cables and adapters included in the box MUST meet ChromeOS Compatible Cable requirements and ChromeOS Compatible Power Adapters requirements[^1] specifications, but need not be officially WWCB certified.

Product Requirements

USB-C

  • If the display supportive native USB-C, it MUST pass the associated requirements in the ChromeOS Compatible Dock spec
    • The display MUST meet DP Alt-Mode requirements
    • If the display supports Power Source role, it MUST pass "Power" requirements
    • If daisy chaining or video out from the display is supported, "HDMI out" and/or "DisplayPort out" requirements MUST be met as well as MST requirements
    • If the display has native USB-A ports, the "USB-A" and "USB and PD Behaviors" requirements MUST be met

Protocols and Compliance

  • The display MUST default to the highest version of any connection protocol it supports.
    • For example, if the display supports DP1.2, it cannot default to DP1.1
  • All inputs of the display SHOULD support the full resolution and refresh rate advertised in Extended Display Identification Data (EDID) specification available to download for the VESA members at their site [VESA Standards]
    • For example, some "4k60" displays only offer 4k60 over DP, and limit HDMI to 4k30 due to HDMI 1.4
    • In the above case, if the display supports 4K60, it SHOULD have support for DP 1.2 on DP port and HDMI 2.0 on HDMI port
    • Similarly, if the DP input supports 4k60, the USB-C input SHOULD also support 4k60 (in appropriate Pin Configuration given signaling constraints)
  • If the display implements HDMI, then the display MUST implement HDMI Forum spec and pass HDMI Forum Compliance Test Suite for the HDMI version implemented.
  • If the display implements DisplayPort (DP), then the display MUST implement VESA spec and pass VESA Link Layer and PHY conformance for the DP version implemented. The VESA CTS specifications are available to the VESA members for download at VESA Standards: https://groups.vesa.org/wg/AllMem/home/get-vesa-standards

HPD

  • Toggling of HDP signals for status change notification MUST follow section 5.2.4 of the VESA DP 2. Specification available to VESA members for download at [VESA Standards]
  • Timing between HPD and DPCD/DDC MUST meet HDMI and DisplayPort standards
    • Both HDMI 1.4b Section 8.5 and DisplayPort 2.0 Section 2.12 specify immediate availability upon HPD signal assertion.
    • These specs are available to VESA members for download at [VESA Standards]
  • Passive HPD MUST be supported
    • HPD MUST be asserted on all the inputs whenever the display is connected to any input

DPRX

  • If the display supports DisplayPort
    • The display MUST support down spread (De-spreading of the Regenerated Stream Clock)
      • Display MUST indicate it is capable of supporting down-spread link frequency in the DPCD by setting MAX_DOWNSPREAD bit.
    • The OUI MUST be properly set
      • For example, the OUI MAY not be all zeros

Power

  • When the display is put to sleep by the connected Chromebook, then it MUST wake when the connected Chromebook sends the wake signal.. This means the display MUST NOT have "deep sleep" states which are automatically entered and require the user to push a button on the display to wake it up.
    • On DisplayPort, the Chromebook will enter/exit sleep via the SET_POWER_STATE bit in DPCD register 00600h SET_POWER
    • On HDMI, the Chromebook will enter/exit sleep via valid video signal on the wire

Identification

  • The display's EDID MUST be valid and parse without errors
  • Display EDID MUST meet the CTA-861-G spec
  • For DP connections, EDID MUST pass VESA EDID Compliance Test Specification v1.2
  • EDID MUST report exactly one set of Manufacturer and Model information
  • EDID MAY include display Name descriptor block containing the proper model name
  • EDID MUST include a valid, non-zero value in the serial number field of Block 0 or the Serial Number extended block
  • Each Manufacturer/Model pair MUST be unique to a given model
  • Each Manufacturer/Model/Serial tuple MUST be universally unique
  • The RGBW color coordinates in EDID MUST agree with the display color spec typical value
  • The display MUST output sRGB if it advertises sRGB in the EDID Feature Support Detail byte (18h)
  • The display MUST advertise one and only one mode marked as preferred per EDID decode level
  • The preferred mode SHOULD be the native resolution of the panel
  • All preferred modes SHOULD match the native aspect ratio of the panel
  • The EDID MUST report the accurate physical dimensions for the display panel not including bezel in centimeters

HDCP

  • The display MUST support HDCP 1.4
  • The display SHOULD support HDCP 2.2
  • The display MAY support HDCP 2.3 or later
  • If the display is a 4K display or greater, the display MUST support HDCP 2.2
  • The display MUST support the same HDCP version(s) on all inputs
  • The display SHOULD have no discernable flicker (0 frames) when HDCP is enabled or disabled

HDR

  • If the display supports HDR, the display MUST meet the VESA DisplayHDR specification for the HDR level claimed by the display
  • If the display supports HDR, the display MUST have infoframe support
  • If the display supports HDR, the display SHOULD support a 10 bit color space
  • If the display supports HDR, the display MAY support a 12 bit color space

Audio

  • If the display supports both built-in speaker and 3.5mm headphone output, it SHOULD support switching between them via either user-directed or automatic methods
  • If the display supports audio input, the display MUST have infoframe support
  • If the display supports audio input, the display SHOULD at least support 2ch, 16-bit, 48K sampling rate audio format, and report the format in EDID

VRR

  • If the display supports VRR/ VESA Adaptive Sync, the display MUST advertise VRR display range (min and max refresh rates) in the EDID display range descriptor block
  • If the display supports VRR/ VESA Adaptive Sync, as per the VESA specification the display MUST set MSA_TIMING_PAR_IGNORED bit in the DOWN_STREAM_PORT_COUNT register (DPCD Address 00007h, bit 6).

Revision History

Date Version Notes
2024-02-01 1.0.1 Republication on a new platform
2023-10-18 1.0 Initial Partner Site Publication