[Mesa-dev] Ivybridge support for ARB_transform_feedback2

[Kenneth Graunke]

On 10/21/2013 08:40 AM, Ian Romanick wrote:
> On 10/17/2013 11:09 PM, Kenneth Graunke wrote:
>> Here's my implementation of ARB_transform_feedback2.  I believe it's
>> complete; it passes all of our Piglit tests and a lot of Intel's
>> oglconform tests.
>>
>> This should work out of the box on Ivybridge and Baytrail.  It won't
>> work on Haswell at the moment, due to restrictions on register writes
>> (to be solved in a future kernel version).  Patch 9 will need to be
>> replaced with something that detects whether or not we can write
>> registers from userspace batchbuffers.
>>
>> In the meantime, I figured I'd send out the rest for review.
>>
>> Porting this back to Sandybridge is probably doable, but annoying.
>> Sandybridge doesn't have the MI_LOAD_REGISTER_MEM command, so we'd have
>> to map the buffers and use MI_LOAD_REGISTER_IMM.  Seems pretty gross.
>> Plus, transform feedback is done very differently pre-Ivybridge.  I'm
>> not sure it's worth it, seeing as it's a GL 4.0 feature.
> 
> I assume this is just to support glDrawTransformFeedback?

No, it's to support glResumeTransformFeedback.

glDrawTransformFeedback actually just reads pipeline statistics counters
and leaves them free-running.

> Can you add that information to http://dri.freedesktop.org/wiki/I965Todo/ ?

Actually, I'm probably wrong...on Gen7 we use MI_LOAD_REGISTER_MEM to
copy offsets into the SO_WRITE_OFFSET(n) registers.  But on Sandybridge,
XFB is done using the geometry shader, so it works entirely differently.
 I don't think there is a register to load.

I'll just let whoever looks into it figure it out.  Not much insight anyway.

--Ken