[Mesa-dev] [PATCH 0/9] i965/gen7 geometry shader support, series 4

[Kenneth Graunke]

On 09/09/2013 08:20 AM, Paul Berry wrote:
> This is the next installment of geometry shader support for i965 gen7.
> Patches 1-2 are a rewrite of patches 21-22 of series 3 (confusingly
> called "Initial geometry shader support, part 2" on the mailing
> list--sorry about that), modified according to Ken's comments.  Once
> these two patches land, i965/gen7 users should be able to try out
> geometry shaders by setting the environment variables:
> 
> MESA_GL_VERSION_OVERRIDE=3.2
> MESA_GLSL_VERSION_OVERRIDE=150
> 
> Patches 3-9 implement EndPrimitive() functionality.  This is tricky on
> gen7 since all geometry shader output vertices are buffered in the URB
> until the thread terminates, and then they are all processed as one
> unit by the fixed function pipeline.  The hardware requires us to keep
> track of when EndPrimitive() was called relative to EmitVertex(), and
> populate a bitfield at the top of the URB with that information.  The
> bitfield has one bit per vertex, indicating 0 if EndPrimitive() wasn't
> called after emitting that vertex, 1 if it was.
> 
> It's difficult in GEN assembly to address a bitfield whose size is
> greater than 32 bits, so we prepare 32 EndPrimitive bits at a time,
> and write them out to the URB as soon as each batch of 32 bits is
> completed.  This requires a little extra bookkeeping, but IMHO it's
> much less work than if we'd tried to maintain all 256 bits in
> registers and output them at the end.  Also, an advantage of the "32
> bits at a time" scheme is that most of the extra bookkeeping goes away
> for the common case of geometry shaders that set max_vertices <= 32.
> 
> [PATCH 1/9] i965/gen7: Extract a function for setting up a shader stage's constants.
> [PATCH 2/9] i965/gs: Add a state atom to set up geometry shader state.
> [PATCH 3/9] glsl: During linking, record whether a GS uses EndPrimitive().
> [PATCH 4/9] i965/gs: Set control data header size/format appropriately for EndPrimitive().
> [PATCH 5/9] i965/gen7: Allow URB_WRITE channel masks to be used.
> [PATCH 6/9] i965/gen7: Add the ability to send URB_WRITE_OWORD messages.
> [PATCH 7/9] i965/gs: Add opcodes needed for EndPrimitive().
> [PATCH 8/9] i965/vec4: Add the ability to emit opcodes with just a dst register.
> [PATCH 9/9] i965/gs: implement EndPrimitive() functionality in the visitor.

Other than the comments I've made so far, patches 1-8 are:
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

I started reading patch 9, but am having some trouble working through
the math.  I'll try and come back to it when I'm more awake.