[Bug 94685] Recent change makes Xorg hangs

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94685

--- Comment #9 from Joakim Tjernlund <joakim.tjernlund at infinera.com> ---
(In reply to Chris Wilson from comment #4)
> So I think it was just because the test should be for 31bits and not 32bits
> (or at least you hit the same bug I just reproduced in a testcase here):
> 
> commit c186d4dda3b62b73af3caf2883a9cedfd97e3b45
> Author: Chris Wilson <chris at chris-wilson.co.uk>
> Date:   Thu Mar 24 18:22:20 2016 +0000
> 
>     sna/present: Restrict vblank.sequence range to 31bits
>     
>     The kernel checks for past vblanks using an int32_t comparison, so we
>     can only program up to 31bits into the future (and similarly programing
>     a timer that large would also overflow).
>     
>     References: https://bugs.freedesktop.org/show_bug.cgi?id=94685
>     Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> The debug log would still be very helpful, thanks.

+ if (warn_unless(msc - swap->msc < 1ull<<31))

Are you not allowed to used the lower bits here(as in 0x7ffffff)?

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