[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 at linaro.org>
>>
>> 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 at linaro.org>
>> Signed-off-by: Steven Price <steven.price at arm.com>
> 
> On the code itself:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
> 
> 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