Re: [PATCH] arm64: dts: ti: k3-am62-mcu: Add power-domains property for M4FSS

[Sidd]

> Anyway, the reason we don't use the normal "power-domains", and instead manage
> the power using `ti,sci-dev-id`, is because the normal power domain framework
> has a nasty habit of unconditionally powering up devices before the driver can
> probe. Which in the case of remoteprocs can cause the core to start running
> and executing random data.

Oh I was not aware of this issue, seemed logical and a straightforward
issue to me, I'll drop this patch then.
I also figured this would in turn nicely move into wrapping all ti sci
handle's device ops through pmruntime (such as get_device and
put_device functions) but I believe that won't work as well.

  > * Power up subsystem
  > * Set reset line for core
  > * Power up the core
  > * Setup the core (load firmware and set boot address)
  > * Release reset line for core to start it running

Right, I see, thanks for the input :)

Thanks,
Siddharth Karanam

On Tue, Sep 29, 2026 at 10:09 PM Andrew Davis <afd@xxxxxx> wrote:
>
> On 9/22/26 12:19 PM, Siddharth Karanam wrote:
> > Assign the power domain to the MCU M4FSS (Cortex-M4F) node by following
> > the device ids info published in TI-SCI public documentation.
> >
> > This will be useful in future patches that will attempt at abstracting
> > ti_sci_dev_ops's calls such as get_device and put_device via pm_runtime
> > calls.
> >
> > Signed-off-by: Siddharth Karanam <sid9.karanam@xxxxxxxxx>
> > ---
> >   arch/arm64/boot/dts/ti/k3-am62-mcu.dtsi | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/boot/dts/ti/k3-am62-mcu.dtsi b/arch/arm64/boot/dts/ti/k3-am62-mcu.dtsi
> > index 68e906796aefe..1ae0870893c16 100644
> > --- a/arch/arm64/boot/dts/ti/k3-am62-mcu.dtsi
> > +++ b/arch/arm64/boot/dts/ti/k3-am62-mcu.dtsi
> > @@ -181,6 +181,7 @@ mcu_m4fss: m4fss@5000000 {
> >                     <0x00 0x5040000 0x00 0x10000>;
> >               reg-names = "iram", "dram";
> >               resets = <&k3_reset 9 1>;
> > +             power-domains = <&k3_pds 7 TI_SCI_PD_EXCLUSIVE>;
>
> The surrounding M4 subsystem's power domain is 7, but the core's power domain number
> is 9 (see below in `ti,sci-dev-id`). Enabling 9 should also enable 7 as it is a
> dependency. We probably should have modeled the M4 in DT the way we did the R5[0].
> With the core being a subnode of the subsystem. Then 7 goes in subsystem and 9
> goes in the core's subnode.
>
> Anyway, the reason we don't use the normal "power-domains", and instead manage
> the power using `ti,sci-dev-id`, is because the normal power domain framework
> has a nasty habit of unconditionally powering up devices before the driver can
> probe. Which in the case of remoteprocs can cause the core to start running
> and executing random data. We have to do things in order,
>
>   * Power up subsystem
>   * Set reset line for core
>   * Power up the core
>   * Setup the core (load firmware and set boot address)
>   * Release reset line for core to start it running
>
> Andrew
>
> [0] https://github.com/torvalds/linux/blob/master/arch/arm64/boot/dts/ti/k3-am62a-mcu.dtsi#L178
>
> >               firmware-name = "am62-mcu-m4f0_0-fw";
> >               ti,sci = <&dmsc>;
> >               ti,sci-dev-id = <9>;
>