linux-kernel - Re: ARM64 TPM start method patches

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Date:   Thu, 13 Apr 2017 23:58:24 -0500
From:   anjiandi@...eaurora.org
To:     Mark Rutland <mark.rutland@....com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Shanker Donthineni <shankerd@...eaurora.org>,
        ard.biesheuvel@...aro.org, harba@...eaurora.org
Subject: Re: ARM64 TPM start method patches

Adding Harb Abdulhamid for SMC details

On 2017-04-11 06:36, Mark Rutland wrote:
> Hi,
> 
> I just stumbled upon the following commits in next-20170411:
> 
>   cf8252ca7ca76fa4 ("ACPICA: Update TPM2 ACPI table")
>   08eff49d63ca2bf4 ("tpm/tpm_crb: Enable TPM CRB interface for ARM64")
> 
> ... which leave me a little concerned, for two reasons.
> 
> Firstly, the spec these are based on (TCG ACPI Specification Family
> “1.2” and “2.0” Version 1.2, Revision 8), is a draft, open for public
> review until April 28th 2017 [1], and still subject to change, as noted
> in the title page of the document [2]:
> 
>     This document is an intermediate draft for comment only and is
>     subject to change without notice. Readers should not design 
> products
>     based on this document.
> 
> ... so I hope the plan is not to merge these until the final spec is
> published.
> 
> Secondly, the spec is very vague as to the workings of the SMC call, 
> and
> does not define:
> 
>  * That the SMC call follows the SMC Calling Convention [3]
>  * The parameters to the SMC call
>  * The return value(s) of the SMC call
> 
> ... which I believe should be clarified in the spec before we make
> assumptions regarding these in the Linux driver. Otherwise, this is
> liable to vary in practice.
> 
> Thanks,
> Mark.
> 
> [1] https://trustedcomputinggroup.org/specifications-public-review/
> [2]
> https://trustedcomputinggroup.org/wp-content/uploads/TCG_ACPIGeneralSpecification-Family-1.2-and-2.0-Ver1.2-Rev8_public-revie....pdf
> [3]
> http://infocenter.arm.com/help/topic/com.arm.doc.den0028b/ARM_DEN0028B_SMC_Calling_Convention.pdf