Video bandwidth is precious.  In particular the HDMI standards seem to 
lag in providing the bandwidth I need.  Partly because I run old hardware.

One silly wast of bandwidth is blanking intervals.  That mattered for CRTs 
since steering the electron beam took time.  It should not matter for 
LCDs.

CVT-RB (Coordinated Video Timings - Reduced Blanking) is a standard for 
reducing the blanking intervals.  It sometimes makes the difference for 
supporting UltraHD. 
<https://en.wikipedia.org/wiki/Coordinated_Video_Timings#Bandwidth>


I haven't yet fiddled with this.  Perhaps it is currently optimal on my 
systems.  But I have had mysterious troubles getting UltraHD working on 
some systems.

The linux cvt(1) command has a flag --reduce:

    Create a mode with reduced blanking. This allows for higher frequency 
    signals, with a lower or equal dotclock. Not for Cathode Ray Tube 
    based displays though.

But I don't think that command is used in my (automatically generated) 
configurations.

Does Linux automatically know when to use CVT-RB?
If so, how does it know?
If not, how do you tell it?

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