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

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Message-ID: <E37DFCB0-2E74-45F6-B2DF-70EF59F310BC@gmx.de>
Date:   Mon, 07 Aug 2017 13:52:34 +0200
From:   Peter Huewe <peterhuewe@....de>
To:     Nayna Jain <nayna@...ux.vnet.ibm.com>,
        tpmdd-devel@...ts.sourceforge.net
CC:     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] tpm: improve tpm_tis send() performance by ignoring burstcount



Am 7. August 2017 13:46:32 MESZ schrieb Nayna Jain <nayna@...ux.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@...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>

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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