Comment by simoncion

(I'm posting in a reply in part because the edit window is long since past.)

Yeah. I'm actually quite interested in hearing what "workarounds" and/or misbehavior you're talking about. 'amdgpu(4)' says this about the TearFree property:

       Option "TearFree" "boolean"
              Set the default value  of  the  per-output  ’TearFree’  property,
              which  controls  tearing prevention using the hardware page flip‐
              ping mechanism.  TearFree is on for any CRTC associated with  one
              or  more  outputs with TearFree on.  Two separate scanout buffers
              need to be allocated for each CRTC with TearFree on.  If this op‐
              tion is set, the default value of the property is ’on’  or  ’off’
              accordingly.   If this option isn’t set, the default value of the
              property is auto, which means that TearFree  is  on  for  rotated
              outputs,  outputs  with  RandR  transforms applied, for RandR 1.4
              secondary outputs, and if ’VariableRefresh’ is enabled, otherwise
              it’s off.
              

The explicit mention that the "auto" enables TearFree only for secondary outputs and rotated and/or transformed outputs if 'VariableRefresh' is disabled seems to directly contradict what I think you're saying. And if "auto" enables TearFree on secondary displays, my recommendation of "on" certainly also does. But, yeah. I await clarification.