Document why the primary plane is a special case

For instance, i915 requires the primary plane to be enabled.
This commit is contained in:
Simon Ser 2021-08-13 12:38:05 +02:00
parent 8a971695bd
commit 447a9e8921

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@ -52,8 +52,10 @@
*
* In practice, the primary plane is treated separately. This is where layers
* that can't be mapped to any plane (e.g. layer 1 in our example) will be
* composited. The primary plane is the first that will be allocated. Then all
* other planes will be allocated, from the topmost one to the bottommost one.
* composited. The primary plane is the first that will be allocated, because
* some drivers require it to be enabled in order to light up any other plane.
* Then all other planes will be allocated, from the topmost one to the
* bottommost one.
*
* The "zpos" property (which defines ordering between layers/planes) is handled
* as a special case. If it's set on layers, it adds additional constraints on