Date: Thu, 12 Feb 2015 07:25:53 +0200
From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Stefan Berger <stefanb@linux.vnet.ibm.com>
Cc: Peter =?iso-8859-1?Q?H=FCwe?= <PeterHuewe@gmx.de>,
        Ashley Lai <ashley@ashleylai.com>,
        Marcel Selhorst <tpmdd@selhorst.net>,
        tpmdd-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        josh@joshtriplett.org, christophe.ricard@gmail.com,
        jason.gunthorpe@obsidianresearch.com, linux-api@vger.kernel.org,
        trousers-tech@lists.sourceforge.net
Subject: Re: [PATCH] tpm, tpm_tis: fix TPM 2.0 probing
Message-ID: <20150212052553.GB7314@intel.com>
References: <1423059669-31734-1-git-send-email-jarkko.sakkinen@linux.intel.com>
 <201502090008.47986.PeterHuewe@gmx.de>
 <20150209083947.GC29987@intel.com>
 <54D9F6A0.9010905@linux.vnet.ibm.com>
 <20150210125037.GB4313@intel.com>
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On Wed, Feb 11, 2015 at 01:47:01PM -0500, Stefan Berger wrote:
> On 02/10/2015 07:50 AM, Jarkko Sakkinen wrote:
> >On Tue, Feb 10, 2015 at 07:16:32AM -0500, Stefan Berger wrote:
> >>On 02/09/2015 03:39 AM, Jarkko Sakkinen wrote:
> >>>On Mon, Feb 09, 2015 at 12:08:46AM +0100, Peter H?we wrote:
> >>>>Am Mittwoch, 4. Februar 2015, 15:21:09 schrieb Jarkko Sakkinen:
> >>>>>If during transmission system error was returned, the logic was to
> >>>>>incorrectly deduce that chip is a TPM 1.x chip. This patch fixes this
> >>>>>issue. Also, this patch changes probing so that message tag is used as the
> >>>>>measure for TPM 2.x, which should be much more stable.
> >>>>Is it aware that some TPMs may respond with 0x00C1 as TAG for TPM1.2 commands?
> >>>I guess none of the TPM 1.2 command answer with the tag 0x8002?
> >>
> >>FYI: pdf page 26 , section 6.1 explains the predictable return value for a
> >>TPM1.2 command seen by a TPM2
> >>
> >>http://www.trustedcomputinggroup.org/files/static_page_files/8C68ADA8-1A4B-B294-D0FC06D3773F7DAA/TPM%20Rev%202.0%20Part%203%20-%20Commands%2001.16-code.pdf
> >>
> >>Following this:
> >>
> >>Sending a TPM1.2 command to a TPM2 should return a TPM1.2 header (tag =
> >>0xc4) and error code (TPM_BADTAG = 0x1e)
> >>
> >>Sending a TPM 2 command to a TPM 2 will give a TPM 2 tag in the header.
> >>Sending a TPM 2 command to a TPM 1.2 will give a TPM 1.2 tag in the header
> >>and an error code.
> >Thank you for the information. Do you think that for some reason
> >tpm2_probe() shoould instead check that value is not this error
> >instead of checking that tag is 0x80002?
> 
> Following your path, you are checking for TPM2_ST_NO_SESSION (0x8001), which
> looks correct to me. A TPM1.2 would never send this tag back.

OK, perfect :)

>     Stefan

/Jarkko
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