Without atomic modesetting, we have no way to know whether or not our
desired configuration is usable. It might fail for a number of reasons:
scaling limits, bandwidth limits, global resource (e.g. decompression)
unit contention, or really just anything.
Not only this, but there is no good way to ensure that our configuration
actually lands together in the same refresh cycle - hence the 'atomic'
in atomic modesetting. Some drivers implement a synchronously blocking
drmModeSetPlane, whereas others return immediately. Using overlay planes
can thus decimate your framerate.
The pre-atomic API is not extensible either, so we need numerous out
clauses: fail if we're cropping or scaling (sometimes), or changing
formats, or fencing, or ...
Now we've had atomic support stable for a couple of releases, just
remove support for doing anything more fancy than displaying our
composited output and a cursor with drivers which don't support atomic
modesetting.
Support for using overlay planes was already disabled by default when
using the legacy API, and required a debug key combination to toggle it
on by flipping the sprites_are_broken variable. We can ensure that we
never try to use it on legacy by simply ignoring the hotkey when in
legacy mode.
Signed-off-by: Daniel Stone <daniels@collabora.com>
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