[Tinkerphones] Librem 5

rhn opcomali.rhn at porcupinefactory.org
Sat Oct 28 14:14:26 CEST 2017

On Sat, 28 Oct 2017 13:33:17 +0200
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:

> Hi,
> > Am 24.10.2017 um 22:06 schrieb Sebastian Krzyszkowiak <dos at dosowisko.net>:
> > 
> > 
> > BTW. What's the situation with PowerVR closed drivers on GTA04 with
> > current kernels? Unfortunately I got slightly out of touch these days,
> > time to catch up :)  
> there is something which happened almost unnoticed by the community.
> SoC-side drivers have been open source by TI for a long time for OMAP3/4/5
> and other SoC, but the SGX/PVR documentation has just been:
> 	http://web.archive.org/web/20170923050320/http://powervr.gnu.org.ve/doku.php
> (it looks as if the original website went down end of september - you may
> speculate about reasons yourself).
> But I just found this morning:
> 	https://community.imgtec.com/developers/powervr/documentation/
> This looks to be very important (dated 07 Apr 2017):
> 	http://cdn.imgtec.com/sdk-documentation/PowerVR+Instruction+Set+Reference.pdf
> I haven't spent time to look through the other material, but it looks as
> if IMG has become much more open!
> Maybe this material is already sufficient to write an open source firmware
> for the PVR and assembler/compiler for shaders but this is something for
> 3D/GPU experts (you know I am hardware expert and still struggle with Linux
> kernels :).
> BR,
> Nikolaus
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this is a nice find! Quite a few documents there indeed.

As you have said, shaders got suddenly much easier. Still, there's a long way to go from there, as shader ISA is only part of the equation. I had just a skim, but I couldn't immediately find the two other important pieces: communication protocol and, if it's relevant for this GPU, initialization and power features.

What we have here will enable Mesa developers to implement a compiler that will translate OpenGL shaders into something that can run directly on the GPU.

Communication is needed for exchanging memory buffers between CPU and GPU, and submitting the shader code for execution.

Depending on the level of control that firmware has on PVR, replacing it may be necessary. With new NVIDIA cards, nouveau is stuck with power issues: clock speeds can only be altered by signed firmware they have no access to. I haven't seen anything about firmware among the PVR docs.

While I have not been involved with PowerVR development, I remember reading somewhere that the trouble with reverse engineering was related with the multitude of models that differ in unexpected ways - so if these docs seem that PVR is very uniform, then the difficult part is probably not described ;)

I hope that I didn't lie too much here - instead of taking my word, it's better to ask someone more involved what these docs mean. For example nouveau (thank you all for teaching me about GPUs!).


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