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

[Nicolai Hähnle]

On 30.08.2017 16:44, Rob Clark wrote:
> On Wed, Aug 30, 2017 at 10:18 AM, Qiang Yu <yuq825 at gmail.com> wrote:
>> 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.
>>
> 
> that is a bit unfortunate.. and also means you have to create multiple
> versions of uniform buffer if internal driver params change between
> draws but user uniforms did not :-(

Does Lima support uniform buffers? You may be able to put the internal 
driver params into a separate buffer.

Cheers,
Nicolai


> 
> BR,
> -R
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