Re: [PATCH v5 04/19] firmware/psci: Add psci_early_test_conduit()

[Suzuki K Poulose]

On 26/08/2024 11:03, Catalin Marinas wrote:
> On Mon, Aug 19, 2024 at 02:19:09PM +0100, Steven Price wrote:
> > From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> >
> > Add a function to test early if PSCI is present and what conduit it
> > uses. Because the PSCI conduit corresponds to the SMCCC one, this will
> > let the kernel know whether it can use SMC instructions to discuss with
> > the Realm Management Monitor (RMM), early enough to enable RAM and
> > serial access when running in a Realm.
> >
> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > Signed-off-by: Steven Price <steven.price@xxxxxxx>
>
> On the code itself:
>
> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
>
> However, Will has a point and it would be good if we can avoid this
> early setup as much as possible. If it's just the early console used for
> debugging, maybe just pass the full IPA address on the command line and
> allow those high addresses in fixmap. Not sure about the EFI map.

We could delay the RSI init until we have probed the PSCI conduit.
This could be done from setup_arch(), after the psci_{dt,acpi}_init().
This is safe, as the EFI maps are only created later, as an 
early_initcall().

Kind regards
Suzuki