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

Peter Huewe
2017-08-07T11:53:06Z

Am 7. August 2017 13:46:32 MESZ schrieb Nayna Jain <nayna@linux.vnet.ibm.com>:
>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>

Are you sure this is a good idea?
On lpc systems this more or less stalls the bus, including keyboard/mouse (if connected via superio lpc).

On which systems have you tested this?
Spi/Lpc? Architecture?

This might not be noticable for small transfers, but think about much larger transfers....

Imho: NACK from my side.

Thanks,
Peter

>---
>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:

--
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