[PATCH v4 2/4] tpm: ignore burstcount to improve tpm_tis send() performance

[Alexander.Steffen at infineon.com]

> On 10/20/2017 08:12 PM, Alexander.Steffen at infineon.com 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.
> >>
> >> This patch optimizes the tpm_tis_send_data() function by checking
> >> the burstcount only once. And if the burstcount is valid, it writes
> >> all the bytes at once, permitting wait state.
> >>
> >> After this change, performance on a TPM 1.2 with an 8 byte
> >> burstcount for 1000 extends improved from ~41sec to ~14sec.
> >>
> >> Suggested-by: Ken Goldman<kgold at linux.vnet.ibm.com>  in
> >> conjunction with the TPM Device Driver work group.
> >> Signed-off-by: Nayna Jain<nayna at linux.vnet.ibm.com>
> >> Acked-by: Mimi Zohar<zohar at linux.vnet.ibm.com>
> >> ---
> >>   drivers/char/tpm/tpm_tis_core.c | 42 +++++++++++++++------------------
> ----
> >> ----
> >>   1 file changed, 15 insertions(+), 27 deletions(-)
> >>
> >> diff --git a/drivers/char/tpm/tpm_tis_core.c
> >> b/drivers/char/tpm/tpm_tis_core.c
> >> index b33126a35694..993328ae988c 100644
> >> --- a/drivers/char/tpm/tpm_tis_core.c
> >> +++ b/drivers/char/tpm/tpm_tis_core.c
> >> @@ -316,7 +316,6 @@ 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;
> >> -	size_t count = 0;
> >>   	bool itpm = priv->flags & TPM_TIS_ITPM_WORKAROUND;
> >>
> >>   	status = tpm_tis_status(chip);
> >> @@ -330,35 +329,24 @@ static int tpm_tis_send_data(struct tpm_chip
> *chip,
> >> u8 *buf, size_t len)
> >>   		}
> >>   	}
> >>
> >> -	while (count < len - 1) {
> >> -		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);
> >> -		rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv-
> >>> locality),
> >> -					 burstcnt, buf + count);
> >> -		if (rc < 0)
> >> -			goto out_err;
> >> -
> >> -		count += burstcnt;
> >> -
> >> -		if (wait_for_tpm_stat(chip, TPM_STS_VALID, chip-
> >>> timeout_c,
> >> -					&priv->int_queue, false) < 0) {
> >> -			rc = -ETIME;
> >> -			goto out_err;
> >> -		}
> >> -		status = tpm_tis_status(chip);
> >> -		if (!itpm && (status & TPM_STS_DATA_EXPECT) == 0) {
> >> -			rc = -EIO;
> >> -			goto out_err;
> >> -		}
> >> +	/*
> >> +	 * Get the initial burstcount to ensure TPM is ready to
> >> +	 * accept data.
> >> +	 */
> >> +	burstcnt = get_burstcount(chip);
> >> +	if (burstcnt < 0) {
> >> +		dev_err(&chip->dev, "Unable to read burstcount\n");
> >> +		rc = burstcnt;
> >> +		goto out_err;
> >>   	}
> >>
> >> +	rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
> >> +			len - 1, buf);
> >> +	if (rc < 0)
> >> +		goto out_err;
> >> +
> >>   	/* write last byte */
> >> -	rc = tpm_tis_write8(priv, TPM_DATA_FIFO(priv->locality),
> >> buf[count]);
> >> +	rc = tpm_tis_write8(priv, TPM_DATA_FIFO(priv->locality), buf[len-
> >> 1]);
> >>   	if (rc < 0)
> >>   		goto out_err;
> >>
> >> --
> >> 2.13.3
> > This seems to fail reliably with my SPI TPM 2.0. I get EIO when trying to
> send large amounts of data, e.g. with TPM2_Hash, and subsequent tests
> seem to take an unusual amount of time. More analysis probably has to wait
> until November, since I am going to be in Prague next week.
> 
> Thanks Alex for testing these.. Did you get the chance to do any further
> analysis ?

I am working on that now. Ken's suggestion seems reasonable, so I am going to test whether correctly waiting for the flags to change fixes the problem. If it does, I'll send the patches.

Alexander
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