[Mesa-stable] [PATCH] i965: Create a hardware context before initializing state module.

[Kenneth Graunke]

On 02/19/2014 06:05 PM, Ian Romanick wrote:
> On 02/19/2014 05:40 PM, Kenneth Graunke wrote:
>> brw_init_state() calls brw_upload_initial_gpu_state().  If hardware
>> contexts are enabled (brw->hw_ctx != NULL), this will upload some
>> initial invariant state for the GPU.  Without hardware contexts, we
>> rely on this state being uploaded via atoms that subscribe to the
>> BRW_NEW_CONTEXT bit.
>>
>> Commit 46d3c2bf4ddd227193b98861f1e632498fe547d8 accidentally moved
>> the call to brw_init_state() before creating a hardware context.
>> This meant brw_upload_initial_gpu_state would always early return.
>> Except on Gen6+, we stopped uploading the initial GPU state via
>> state atoms, so it never happened.
>>
>> Fixes a regression since 46d3c2bf4ddd227193b98861f1e632498fe547d8.
> 
> This seems like a rational change... but why didn't 46d3c2b blow up the
> world on IVB and HSW?  ...and only cause heisenbugs on BDW?

Presumably because it doesn't do much.  On Gen6+, all it does is:
- PIPELINE_SELECT (probably already render, unless you're doing media/gpgpu)
- STATE_SIP (basically only matters if you hit breakpoints or invalid
operations)
- VF_STATISTICS (we don't use the counters anyway)

On Broadwell, it also uploads 3DSTATE_SAMPLE_PATTERN, which meant that
any Piglit test that relied on legitimate sample positions would fail.
That is, until I ran with a branch that actually emitted
3DSTATE_SAMPLE_PATTERN---after that, the sample positions remained
programmed, and tests continued to work fine until reboot.

>> Cc: "10.0 10.1" <mesa-stable at lists.freedesktop.org>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> 
> Either way,
> 
> Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>


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