[Mesa-dev] [PATCH] i965: Fix GPU hangs when a blorp batch is the first thing to execute.

[Chris Wilson]

On Thu, May 02, 2013 at 07:26:06AM -0700, Paul Berry wrote:
>    Can you provide a documentation reference for why the value we're
>    currently programming (0xfffff001) is unsafe, and why 0x7fff0001 is
>    correct?� I don't see anything in the bspec.

The largest GTT size for gen6 is 2GiB (it can be smaller on the whim of
the BIOS, though we try to reset it back to 2GiB in i915.ko). The upper
bound is used by the hardware to prevent invalid reads and return 0,
this is the value we program to ~4GiB. The cause of these hangs is the
constant data being read from addresses above 2GiB i.e. beyond the end
of the GTT - and so prevented by programming the upper bound to the end
of the GTT. Those with access to the simulator can hopefully verify
this, and perhaps we should add this to the set of known bad commands in
igt.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre