[Bug 102774] [BDW] [Bisected] Absolute constant buffers break VAAPI in mpv

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102774

--- Comment #18 from Kenneth Graunke <kenneth at whitecape.org> ---
(In reply to Maxim Baz from comment #17)
> Hey Kenneth, has there been any traction on reverting and/or fixing the code
> during the past 3 weeks? Looks like the thread your created [1] didn't
> receive any attention whatsoever.
> 
> [1]:
> https://lists.freedesktop.org/archives/mesa-stable/2017-September/007116.html

True that.  I sent another patch to revert it off of master last week, which
stirred up a bit of flames, and Kristian apparently convinced at least -some-
kernel people that this needs to be fixed in the kernel.  Whether anything will
happen to that end, I have no idea.

In the meantime, I've pushed my revert to master, with the appropriate marking
for stable branches.  Emil / Andres should pick it up for the 17.3 / 17.2
stable branches soon.

Thanks for your patience, and sorry about this mess. :(

Fixed in master with:

commit 013d33122028f2492da90a03ae4bc1dab84c3ee9
Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Thu Oct 19 14:38:30 2017 -0700

    i965: Revert absolute mode for constant buffer pointers.

    The kernel doesn't initialize the value of the INSTPM or CS_DEBUG_MODE2
    registers at context initialization time.  Instead, they're inherited
    from whatever happened to be running on the GPU prior to first run of a
    new context.  So, when we started setting these, other contexts in the
    system started inheriting our values.  Since this controls whether
    3DSTATE_CONSTANT_* takes a pointer or an offset, getting the wrong
    setting is fatal for almost any process which isn't expecting this.

    Unfortunately, VA-API and Beignet don't initialize this (nor does older
    Mesa), so they will die horribly if we start doing this.  UXA and SNA
    don't use any push constants, so they are unaffected.

    Until we have some kind of solution to this problem, I'm going to revert
    this patch and abandon using the feature for now.  It will lead to fewer
    pushed UBO ranges on Broadwell+, which may lead to lower performance,
    though I don't have any data on the impact.

    Cc: "17.3 17.2" <mesa-stable at lists.freedesktop.org>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102774

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