[PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount

Nayna Jain
2017-08-07T11:47:03Z

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 ignores burstcount, permitting wait states, and thus
writes the command as fast as the TPM can accept the bytes.
The performance of a 34 byte extend on a TPM 1.2 improved from
52 msec to 11 msec.

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 | 45 ++---------------------------------------
1 file changed, 2 insertions(+), 43 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index b617b2eeb080..478cbc0f61c3 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -255,9 +255,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
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;
+ int rc, status;

status = tpm_tis_status(chip);
if ((status & TPM_STS_COMMAND_READY) == 0) {
@@ -270,49 +268,10 @@ 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;
- }
- }
-
- /* write last byte */
- rc = tpm_tis_write8(priv, TPM_DATA_FIFO(priv->locality), buf[count]);
+ rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality), len, buf);
if (rc < 0)
goto out_err;

- 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;
- }
-
return 0;

out_err:
--
2.13.3