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

[Nayna]

On 08/07/2017 05:22 PM, Peter Huewe wrote:
> Am 7. August 2017 13:46:32 MESZ schrieb Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>:
> > 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@xxxxxxxxxxxxxxxxxx> in
> > conjunction with the TPM Device Driver work group.
> > Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
> > Acked-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
>
> 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).

Thanks Peter for quick response.

I actually meant to post this patch as RFC. Sorry, missed that.
It was meant to be a starting place for the discussion related to 
burst_count.

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

Tested it with LPC on x86.

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

I did the following testing:

* Ran a script with 1000 extends. This was to test continuous extends
which are generally in large numbers when IMA is enabled.

* Ran a command to ask TPM to hash big size file like 1MB. This was to
test the long command.

In both of the above cases, I didn't face any tpm specific errors.

Is there any test-script or test-cases which I can try to test the
scenario(stalling the bus, including keyboard/mouse) with the patch ?

Thanks & Regards,
   - Nayna


> 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: