linux-kernel - Re: [PATCH 1/4] tpm: ignore burstcount to improve tpm

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Date:   Wed, 6 Sep 2017 18:28:38 +0530
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     tpmdd-devel@...ts.sourceforge.net
Cc:     peterhuewe@....de, tpmdd@...horst.net,
        jarkko.sakkinen@...ux.intel.com, jgunthorpe@...idianresearch.com,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-ima-devel@...ts.sourceforge.net, patrickc@...ibm.com
Subject: Re: [PATCH 1/4] tpm: ignore burstcount to improve tpm_tis send()
 performance.

Please ignore these one.. My command took patches recursively from 
directory also.

Sorry for this.

Thanks & Regards,
    - Nayna

On 09/06/2017 06:26 PM, Nayna Jain wrote:
> The TPM burstcount status indicates the number of bytes that can
> be sent to the TPM without causing bus wait states.  Effectively,
> it is the number of empty bytes in the command FIFO. Further,
> some TPMs have a static burstcount, when the value remains zero
> until the entire FIFO is empty.
>
> This patch adds an optimization to check for burstcount only once.
> And if it is valid, it writes all the bytes at once, permitting
> wait states. The performance of a 34 byte extend on a TPM 1.2 with
> an 8 byte burstcount improved from 41 msec to 14 msec.
>
> This functionality is enabled only by passing module
> parameter ignore_burst_count=1. By default, this parameter
> is disabled.
>
> Suggested-by: Ken Goldman <kgold@...ux.vnet.ibm.com> in
> conjunction with the TPM Device Driver work group.
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
> Acked-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> ---
>   Documentation/admin-guide/kernel-parameters.txt |  8 ++++++++
>   drivers/char/tpm/tpm_tis_core.c                 | 24 +++++++++++++++++++++---
>   2 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 4e303be83df6..3c59bb91e1ee 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1465,6 +1465,14 @@
>   			mode generally follows that for the NaN encoding,
>   			except where unsupported by hardware.
>
> +	ignore_burst_count [TPM_TIS_CORE]
> +			tpm_tis_core driver queries for the burstcount before
> +			every send call in a loop. However, it causes delay to
> +			the send command for TPMs with low burstcount value.
> +			Setting this value to 1, will make driver to query for
> +			burstcount only once in the loop to improve the
> +			performance. By default, its value is set to 0.
> +
>   	ignore_loglevel	[KNL]
>   			Ignore loglevel setting - this will print /all/
>   			kernel messages to the console. Useful for debugging.
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 63bc6c3b949e..6b9bf4c4d434 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -31,6 +31,11 @@
>   #include "tpm.h"
>   #include "tpm_tis_core.h"
>
> +static bool ignore_burst_count = false;
> +module_param(ignore_burst_count, bool, 0444);
> +MODULE_PARM_DESC(ignore_burst_count,
> +		"Ignore burstcount value while writing data");
> +
>   /* Before we attempt to access the TPM we must see that the valid bit is set.
>    * The specification says that this bit is 0 at reset and remains 0 until the
>    * 'TPM has gone through its self test and initialization and has established
> @@ -256,6 +261,7 @@ static int tpm_tis_send_data(struct tpm_chip *chip, u8 *buf, size_t len)
>   {
>   	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>   	int rc, status, burstcnt;
> +	int sendcnt;
>   	size_t count = 0;
>   	bool itpm = priv->flags & TPM_TIS_ITPM_WORKAROUND;
>
> @@ -271,19 +277,31 @@ static int tpm_tis_send_data(struct tpm_chip *chip, u8 *buf, size_t len)
>   	}
>
>   	while (count < len - 1) {
> +
> +		/*
> +		 * Get the initial burstcount to ensure TPM is ready to
> +		 * accept data, even when waiting for burstcount is disabled.
> +		 */
>   		burstcnt = get_burstcount(chip);
>   		if (burstcnt < 0) {
>   			dev_err(&chip->dev, "Unable to read burstcount\n");
>   			rc = burstcnt;
>   			goto out_err;
>   		}
> -		burstcnt = min_t(int, burstcnt, len - count - 1);
> +
> +		if (ignore_burst_count)
> +			sendcnt = len - 1;
> +		else
> +			sendcnt = min_t(int, burstcnt, len - count - 1);
> +
>   		rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
> -					 burstcnt, buf + count);
> +					 sendcnt, buf + count);
>   		if (rc < 0)
>   			goto out_err;
>
> -		count += burstcnt;
> +		count += sendcnt;
> +		if (ignore_burst_count)
> +			continue;
>
>   		if (wait_for_tpm_stat(chip, TPM_STS_VALID, chip->timeout_c,
>   					&priv->int_queue, false) < 0) {
>