linux-kernel - Re: [PATCH 3/3] arm64: acpi: Enable ACPI CCEL support

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Message-ID: <bf56dab4-8a11-4e91-b330-2a8126c94acc@arm.com>
Date: Tue, 15 Jul 2025 15:38:41 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Will Deacon <will@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
 sami.mujawar@....com, aneesh.kumar@...nel.org, steven.price@....com,
 linux-kernel@...r.kernel.org, sudeep.holla@....com
Subject: Re: [PATCH 3/3] arm64: acpi: Enable ACPI CCEL support

On 15/07/2025 14:56, Will Deacon wrote:
> On Fri, Jun 13, 2025 at 12:11:53PM +0100, Suzuki K Poulose wrote:
>> ACPI CCEL memory area is reported as Non-Volatile storage area. Map it as
>> PAGE_KERNEL.
> 
> It would be helpful to have a citation for that. I've tried digging it
> out of the ACPI spec, but that pointed me to the Intel TDX site and I
> got lost in whitepapers :/
> 

https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#cc-event-log-acpi-table

>> Cc: Sami Mujawar <sami.mujawar@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
>> Cc: Steven Price <steven.price@....com>
>> Cc: Sudeep Holla <sudeep.holla@....com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>   arch/arm64/kernel/acpi.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
>> index b9a66fc146c9..f52439d411a0 100644
>> --- a/arch/arm64/kernel/acpi.c
>> +++ b/arch/arm64/kernel/acpi.c
>> @@ -356,6 +356,11 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
>>   			prot = PAGE_KERNEL_RO;
>>   			break;
>>   
>> +		case EFI_ACPI_MEMORY_NVS:
>> +			/* Non-volatile storage, required for CCEL */
>> +			prot = PAGE_KERNEL;
> 
> By "storage" you just mean memory, right?

Yep, it is just memory. I will drop the "NV storage" and simply mention, 
CCEL.

Thanks!

Suzuki


> 
> Will