Re: [PATCH v5 3/3] arm64: dts: qcom: sm8750: Add GPU clock & IOMMU nodes

[Pengyu Luo]

On Tue, Mar 10, 2026 at 9:32 PM Konrad Dybcio
<konrad.dybcio@xxxxxxxxxxxxxxxx> wrote:
>
> On 3/9/26 11:27 AM, Pengyu Luo wrote:
> > On Thu, Mar 5, 2026 6:40 PM Taniya Das <taniya.das@xxxxxxxxxxxxxxxx> wrote:
> >> From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> >>
> >> Add the GPU_CC and GX_CC (brand new! as far as we're concerned, this
> >> is simply a separate block housing the GX GDSC) nodes, required to
> >> power up the graphics-related hardware.
> >>
> >> Make use of it by enabling the associated IOMMU as well. The GPU itself
> >> needs some more work and will be enabled later.
> >>
> >> Reviewed-by: Abel Vesa <abel.vesa@xxxxxxxxxxxxxxxx>
> >> Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>
> >> Co-developed-by: Taniya Das <taniya.das@xxxxxxxxxxxxxxxx>
> >> Signed-off-by: Taniya Das <taniya.das@xxxxxxxxxxxxxxxx>
> >> ---
> >>
> >
> > Hi Taniya and Konrad, GX GDSC stuck at 'on' on my device
> > the raw register values are
> >
> > 0x3d68024: 0x00000000
> > 0x3d68028: 0x00000000
>
> These likely indicate that some clock or voltage rail is not accessible
> at the very moment you're reading them back
>

It seems to be harmless. In the downstream, they are always zero too.
TB322FC:/ # devmem 0x3d68024
0x00000000
TB322FC:/ # devmem 0x3d68028
0x00000000

In [1], the commit log mentioned
The GX GDSC is modelled to aid the GMU in powering down the GPU in the
event that the GPU crashes.

> GPU support for 8750 is not yet upstream (and A830 is somewhat different
> vs the supported A840) - there may be something wrong in that sequence.
>

Indeed. Chances are that I can't enable gpu. I must reboot again and again to
match the sequence by luck, then I can enable it[2], and I must
disable register protection.(I just noticed the hack from here[3])

> I heard it's in the works though, so you may be better off waiting a bit.
>

Glad to hear that. I am looking forward to it.

Slightly off-topic, do you know if anyone is working on wcn786x/wcn7880,
sm8750 QRD SKU2 V8 Power Grid uses this.

[1]: https://lkml.org/lkml/2024/1/23/1408
[2]: https://postimg.cc/xJr11DK5
[3]: https://github.com/gio3k/linux/commit/f96512ab05a1bcc6b7e82b27f44d907238fc64fb

Best wishes,
Pengyu