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SubjectRE: [PATCH v4 2/4] tpm: ignore burstcount to improve tpm_tis send() performance
Date
> 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@linux.vnet.ibm.com> in
> conjunction with the TPM Device Driver work group.
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
> Acked-by: Mimi Zohar <zohar@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.

Alexander

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