[Nouveau] Fermi+ shader header docs

[Ilia Mirkin]

On Thu, May 21, 2015 at 11:32 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Thu, May 21, 2015 at 10:05 AM, Robert Morell <rmorell at nvidia.com> wrote:
>> Hi Ilia,
>>
>> On Sat, May 02, 2015 at 12:34:21PM -0400, Ilia Mirkin wrote:
>>> Hi,
>>>
>>> As I'm looking to add some support to nouveau for features like atomic
>>> counters and images, I'm running into some confusion about what the
>>> first word of the shader header means. Here is the definition as we
>>> have it today:
>>
>> [...]
>>
>>> However I know that these are somewhat wrong. I've seen shaders that
>>> use gmem accesses (i.e. mov r0, [r0]) that just have the LMEM enable
>>> bit set (and they use no lmem). And I've seen additional bits set, esp
>>> relating to images, but I haven't spent enough time looking at all the
>>> variations to make sense of it yet. For example, I think that Fermi
>>> and Kepler+ have different meanings for some of the bits.
>>
>> Those look pretty close :)
>>
>>> I was hoping you could just release the docs for the shader headers,
>>> or at least the first word of the shader header.
>>
>> We've posted the specification for the full Shader Program Header to our
>> GPU documentation site here:
>>
>> ftp://download.nvidia.com/open-gpu-doc/Shader-Program-Header/1/Shader-Program-Header.html
>>
>> I hope it helps clear things up.
>
> Yep, just a few follow-up questions:
>
> - SPH Type 1 and type 2 appear to be flipped wrt the tables -- "When
> PS is used, field SphType in CommonWord0 must be set to 1; similarly,
> when VTG is used, SphType in CommonWord0 must be set to 2." But the
> "Table 1. SPH Type 1 Definition" is clearly meant for VTG and table 2
> is clearly meant for PS...
> - You skip over SassVersion -- what is that?
> - You have a funny note in there -- "Triangles generated by the
> geometry shader always have all their edge flags set to TRUE" -- that
> is the *only* reference to edge flags in the whole document. Right now
> we do some crazy thing to get edge flags right on fermi+ (and I think
> we just get them wrong on tesla). Is there a way to emit edge flags
> from vertex shader?
> - To be clear: DoesLoadOrStore -- *any* load/store? Even LDC? ALD?

Oh, and one more little correction:

"""
The SPH field OutputTopology sets the primitive topology of the
vertices that are output from the pipe stage. This field is only used
with geometry shaders, where the value must be greater than zero and
has a maximum of 1024. The allowed values are: ... [the correct values
for OutputTopology]
"""

The 1024 thing seems like it probably applies to MaxOutputVertexCount
in CommonWord4.

  -ilia