[PATCH xserver 1/2] modesetting: Fix reverse prime partial update issues on secondary GPU outputs

[Eric Anholt]

Keith Packard <keithp at keithp.com> writes:

> Hans de Goede <hdegoede at redhat.com> writes:
>
>> So it looks like we really need glFinish to ensure proper ordering here
>> (and I've just deleted the v2 of this patchset with flush with I had
>> prepared).
>
> If you need glFinish, then your drivers are broken. glFlush and suitable
> fences provides sufficient information to allow for synchronization
> between operations without also requiring waiting for the hardware to
> finish. It's a difference between getting things into the hardware
> queues in the right order and waiting for those hardware queues to
> drain.

glFlush by the spec does provide any guarantees that things have made it
to the kernel.  We have just assumed that, but I think the Radeon driver
may be violating that assumption these days.
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