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Date: Fri, 13 Sep 2024 14:52:39 +0100
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Subject: Re: [PATCH v5 04/19] firmware/psci: Add psci_early_test_conduit()
To: Catalin Marinas <catalin.marinas@arm.com>,
 Steven Price <steven.price@arm.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, Marc Zyngier
 <maz@kernel.org>, Will Deacon <will@kernel.org>,
 James Morse <james.morse@arm.com>, Oliver Upton <oliver.upton@linux.dev>,
 Zenghui Yu <yuzenghui@huawei.com>, linux-arm-kernel@lists.infradead.org,
 linux-kernel@vger.kernel.org, Joey Gouly <joey.gouly@arm.com>,
 Alexandru Elisei <alexandru.elisei@arm.com>,
 Christoffer Dall <christoffer.dall@arm.com>, Fuad Tabba <tabba@google.com>,
 linux-coco@lists.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>,
 Gavin Shan <gshan@redhat.com>, Shanker Donthineni <sdonthineni@nvidia.com>,
 Alper Gun <alpergun@google.com>,
 Jean-Philippe Brucker <jean-philippe@linaro.org>
References: <20240819131924.372366-1-steven.price@arm.com>
 <20240819131924.372366-5-steven.price@arm.com> <ZsxS52IBVVLKrTEX@arm.com>
Content-Language: en-US
From: Suzuki K Poulose <suzuki.poulose@arm.com>
In-Reply-To: <ZsxS52IBVVLKrTEX@arm.com>
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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@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@linaro.org>
>> Signed-off-by: Steven Price <steven.price@arm.com>
> 
> On the code itself:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@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