linux-kernel - Re: [PATCH v4 2/4] tpm: ignore burstcount to improve tpm

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Date:   Tue, 28 Nov 2017 22:19:03 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Leendert van Doorn <leendert@...amecium.org>
Cc:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Nayna Jain <nayna@...ux.vnet.ibm.com>,
        "Alexander.Steffen@...ineon.com" <Alexander.Steffen@...ineon.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterhuewe@....de" <peterhuewe@....de>,
        "tpmdd@...horst.net" <tpmdd@...horst.net>,
        "patrickc@...ibm.com" <patrickc@...ibm.com>,
        "Safford, David (GE Global Research, US)" <david.safford@...com>
Subject: Re: [PATCH v4 2/4] tpm: ignore burstcount to improve tpm_tis send()
 performance

On Mon, Nov 27, 2017 at 07:08:51AM +0000, Leendert van Doorn wrote:
> Hmm, this is almost 20 years old code (
> 
> I think the original code did a burst write and didn't check for error
> conditions until the very last byte write. I seem to remember that
> there was some text in the original standard to that effect (this may
> have gone back as far as IBM's ESS spec).
> 
> The current code does check for error conditions after each write
> byte(s) so I don't think there is any reason for this anymore.
> Changing the while condition to count < len and setting burstcnt =
> min_t(int, burstcnt, len - count) and remove the
> tpm_tis_write8/wait_for_tpm_stat/tpm_tis_status clauses after the
> while loop should be sufficient.

Thank you for sharing this!

> 	Leendert

/Jarkko