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

[Qiang Yu]

On Wed, Aug 30, 2017 at 9:03 PM, Rob Clark <robdclark at gmail.com> wrote:
> 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.)
lima store uniform in system memory and can't write memory in
cmd stream, so I have to do a memcpy before draw if not use the
constant buffer of set_constant_buffer.

Regards,
Qiang