When I switched to NVidia I was surprised to find a much more open ecosystem with good public documentation. NVidia did have some tasty secret sauce stuff that they didn't expose outright, but they did what they could to empower developers to make the best use of the underlying hardware.
Just my opinion based on working in both companies for a number of years. Thankfully I no longer have a dog in that fight.
> The HLOS (High-level OS) running on the Hexagon requires every "applet" to be signed by either the Qualcomm root cert or the OEMs cert
That's no longer true since quite some years now :) See the Unsigned PDs, which are allowed for general purpose compute since at least sm8150 (Snapdragon 855).
Note that the articles you mention says this about it:
> Signature-free dynamic shared objects are run inside an Unsigned PD, which is the user PD limited in its access to underlying DSP drivers and thread priorities. An Unsigned PD is designed to support only general computing applications.
I am becoming convinced that CPU (and maybe GPU) is the only viable accelerator on Android devices. All these fancy accelerators are just for phone makers to do their own thing (mainly camera crap). Might as well make it part of the ISP.
Also, I fear Apple is going to eat Android's lunch at this rate :(
The HLOS (High-level OS) running on the Hexagon requires every "applet" to be signed by either the Qualcomm root cert or the OEMs cert. Usually, every phone has a set of generic Hexagon applets (or "skeleton libs") that are provided and signed by the OEM, which seem to be freely usable to offload some computational work to the DSP (mainly FastCV et al - https://developer.qualcomm.com/sites/default/files/docs/qual...). Those of course come with their own bugs: https://research.checkpoint.com/2021/pwn2own-qualcomm-dsp/
On some older SoCs, you were able to use a TOCTOU (Time of check to time of use) exploit to bypass the signature check by patching the applet loader shim in-memory, once it itself got authenticated: https://github.com/geohot/freethedsp/ (I have personally ported this to the msm8953, and it seems to work)