[Mesa-dev] Question about implementing viewport transfer and const load in nir

[Rob Clark]

On Wed, Aug 30, 2017 at 3:26 AM, Qiang Yu <yuq825 at gmail.com> wrote:
>> btw, does lima have some way to write to memory from cmdstream (ie.
>> without setting up a full blown draw)?  If so perhaps you could get
>> away with leaving some extra space at the end of your uniform buffer
>> that you copy driver internal uniforms into before kicking the draw?
> Unfortunately lima can't do this. Seems you guys all know how to
> "reserve space in uniform buffer", how?
>
>>
>> fwiw, freedreno does have driver specific uniforms, see
>> ir3_driver_param.  Although normal uniforms (ie. non-UBO) get copied
>> into internal memory, so I just upload driver specific uniforms (as
>> needed) and immediates to the tail of the uniform memory before the
>> draw.
> So you mean freedreno will do an extra copy from the constant buffer
> set by set_constant_buffer to a driver allocated memory then append
> the driver spec uniform? If so, that can explain the trick above.

Kind of.. it is really a copy into internal uniform memory that the
shaders access.  Although if the uniforms were a buffer in system
memory and you had a way to memcpy from cmdstream synchronized with
draws, then that could work too.  (I do similar w/ some immediates
too, since in some cases it avoids an extra move from immed
instruction in the shader.)

BR,
-R