linux-kernel - Re: [PATCH v5 04/19] firmware/psci: Add psci_early_test

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Message-ID: <2f9f10cf-7356-458a-bf63-ed6a757df81f@arm.com>
Date: Fri, 13 Sep 2024 14:52:39 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Catalin Marinas <catalin.marinas@....com>,
 Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev, Marc Zyngier
 <maz@...nel.org>, Will Deacon <will@...nel.org>,
 James Morse <james.morse@....com>, Oliver Upton <oliver.upton@...ux.dev>,
 Zenghui Yu <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
 Alexandru Elisei <alexandru.elisei@....com>,
 Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 Alper Gun <alpergun@...gle.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v5 04/19] firmware/psci: Add psci_early_test_conduit()

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@...aro.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@...aro.org>
>> Signed-off-by: Steven Price <steven.price@....com>
> 
> On the code itself:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@....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