Re: [PATCH v5 2/5] firmware: tegra: bpmp: Add ACPI support

[Sudeep Holla <sudeep.holla@kernel.org>]

On Tue, Sep 29, 2026 at 09:59:12AM +0000, Aniruddha Rao wrote:
> Add required changes in the Tegra BPMP driver to make it compatible with
> ACPI-based platforms.
> 
> On ACPI systems, IPC is handled through an AML method instead of the
> kernel mailbox and IVC frameworks.
> 
> Clock, reset and power-domain providers are not controlled by the Linux
> BPMP driver on ACPI-based systems, so do not initialize them there.
> 

The above 2 statements are very clear and says this driver is not much
useful on ACPI systems which is good and aligns with the general
expectations.

> Keep transport initialization in the SoC-specific init operation. Use an
> optional init_providers operation for DT child and provider registration
> after BPMP communication has been established and the firmware tag has
> been read. ACPI platforms leave this operation unset.
> 

"ACPI platforms leave this operation unset" - I don't fully understand
what this means ? If it means we need to do something on ACPI systems,
why can't it be done by some boot firmware instead ?

> DT transports register an MRQ_PING handler for requests initiated by
> BPMP firmware. This request direction was used only by a diagnostic
> command in older firmware and is not provided by firmware on ACPI-based
> systems. The ACPI transport therefore does not register an incoming
> handler; its init operation only sends the outgoing MRQ_PING request used
> to verify communication with firmware.
> 

OK, I am more confused as you state more things are not needed on ACPI
systems. Why do we need to add any support for ACPI systems then? Can you
make it clear as what is needed on ACPI systems and why it needs to be
done by OSPM and not any boot firmware if it is just one time initialisation.

-- 
Regards,
Sudeep