[Nouveau] [Bug 103202] Tearing with reverse prime (intel primary, nouveau secondary)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103202

--- Comment #3 from post+fdo at ralfj.de ---
> I'm told that tearing with reverse prime is expected.

That would still be a bug then though?  Clearly some form of synchronization
should be supported.

It seems there is some work on getting synchronization to work with PRIME
<https://www.x.org/wiki/Events/XDC2016/Program/xdc-2016-prime-sync.pdf>; not
sure what the current status of that is.  Some sites make it sound like using
the NVidia card with the proprietary drivers as primary actually can get you
V-sync on both screens, so is this just a matter of getting the nouveau DRM
driver hooked up to that infrastructure?

> if you were to flip them around and run the nvidia board as primary, you'd see tearing on the intel-connected screen.

Possible; I would then also have really bad battery life with no external
screen connected as the NVidia card would keep running.

> -intel/radeon both offer the option to stage that copy into a back buffer for flipping to avoid the tear

Given that the Intel card is the primary here, that wouldn't really help,
right?  I would expect to need such an option for whatever drives the NVidia
card.

> X tears by default.

Well, yes, but with reverse PRIME I get tearing even if the application uses
V-Sync or if I use a compositor.  So, this is not about a lack of
synchronization per default, it is about synchronization never happening even
when using the appropriate APIs.

I wouldn't mind looking into Wayland, but found no indication that reverse
PRIME is supported there at all.

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