linux-kernel - Re: [tpmdd-devel] [PATCH RFC 2/2] tpm: refactor tpm2_get_tpm_pt to tpm2_getcap

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Date:   Thu, 17 Nov 2016 09:42:41 -0800
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Nayna <nayna@...ux.vnet.ibm.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [tpmdd-devel] [PATCH RFC 2/2] tpm: refactor tpm2_get_tpm_pt to
 tpm2_getcap_cmd

On Thu, Nov 17, 2016 at 05:20:36PM +0530, Nayna wrote:

> I tested this for capability TPM2_CAP_PCRS. It seems TPM2_CAP_PCRS
> capability always returns full PCR allocation, and more_data as 0, So, I
> think the idea of looping over based on more_data may not work for this
> capability.

You can always request one value at a time until there's no more.

If you request N values, depending on the hardware, the hardware returns
to you anything from 1 to N values. If you implement a function that
requests N values in the command, you *must* handle the case where
moreData is 1 even if the hardware you are testing that never happens.

That's the reason why I would start with a function that you request one
property of one capability and optimize it in future if it doesn't scale
for some workload.

Do you have a workload where it doesn't scale?

/Jarkko