[PATCH] clk: mediatek: Disable ACP to fix 3D on MT8192

[Chen-Yu Tsai]

Hi,

On Fri, Jan 14, 2022 at 9:47 PM Alyssa Rosenzweig <alyssa at collabora.com> wrote:
>
> > > That links to an internal Google issue tracker which I assume has more
> > > information on the bug. I would appreciate if someone from Google or
> > > MediaTek could explain what this change actually does and why it's
> > > necessary on MT8192.
> > >
> > > At any rate, this register logically belongs to the MT8192 "infra" clock
> > > device, so it makes sense to set it there too. This avoids adding any
> > > platform-specific hacks to the 3D driver, either mainline (Panfrost) or
> > > legacy (kbase).
> >
> > Does this really have anything to do with clocks?
>
> I have no idea. MediaTek, Google, please explain.
>
> > In particular, "ACP" usually refers to the Accelerator Coherency Port
> > of a CPU cluster or DSU, and given the stated symptom of the issue
> > affected by it, my first guess would be that this bit might indeed
> > control routing of GPU traffic either to the ACP or the (presumably
> > non-coherent) main interconnect.
>
> I'd easily believe that.

As Robin guessed, "ACP" here does refer to the Accelerator Coherency Port.
And the bit in infracfg toggles whether ACP is used or not.

Explanation from MediaTek in verbatim:

-------------------------------------------------------------------------
The ACP path on MT8192 is just for experimental only.
We are not intended to enable ACP by design.

But due to an unexpected operation, it was accidently opened by default.
So we need a patch to disable the ACP for MT8192.
-------------------------------------------------------------------------


Regards
ChenYu

> > If that is the case, I think this would logically belong as a SoC-specific
> > quirk in panfrost, where we'd need to retrieve the syscon regmap for
> > ourselves (see around line 800 of drivers/iommu/mtk_iommu.c for a similar
> > example).
>
> Alright. Doing this in panfrost seems ugly but if that's the right place
> for it, that's the right place for it.