[RFC][PATCH 4/9] tpm_tis_core: send all data in single operation

[Alexander Steffen <Alexander.Steffen@infineon.com>]

tpm_tis_send_data splits all commands sent to the TPM into at least two
transfers, even if the commands are small enough to fit into a single
transfer. The intention seems to be to make extra sure that the TPM has
received all data correctly by observing the Expect flag flipping from 1 to
0 when writing the last byte.

Unfortunately, this does not work as intended, because the Expect flag will
change not when the last byte is written to the FIFO, but when the TPM
processes the last byte from the FIFO. With a large FIFO and long commands
it might well be that there are still many bytes left in the FIFO when the
Expect flag is checked. Obviously, the flag will be 1 then, even if the
FIFO contains more bytes than expected. Since there is no indication
whether the FIFO is already empty or not, there is no way to implement this
check reliably.

But then again, this check is not necessary at all. The driver already
ensures that not more data is sent to the TPM than is announced in the
header. In addition, the TPM is required to throw away all extraneous bytes
anyway. So if the Expect flag is 0 after all bytes have been sent to the
TPM, the TPM has received the command correctly and is ready to execute it.

Therefore, remove this intermediary check and send all data in a single
operation. This simplifies the code and improves the performance,
especially for short commands.

Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
---
 drivers/char/tpm/tpm_tis_core.c | 25 ++++++-------------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 0df05b4..1359c52 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -320,7 +320,6 @@ static int tpm_tis_send_data(struct tpm_chip *chip, const 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);
 	if ((status & TPM_STS_COMMAND_READY) == 0) {
@@ -333,38 +332,26 @@ static int tpm_tis_send_data(struct tpm_chip *chip, const u8 *buf, size_t len)
 		}
 	}
 
-	while (count < len - 1) {
+	while (count < len) {
 		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);
+		burstcnt = min_t(int, burstcnt, len - count);
 		rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
 					 burstcnt, buf + count);
 		if (rc < 0)
 			goto out_err;
 
 		count += burstcnt;
-
-		if (!itpm && wait_for_tpm_stat
-			     (chip, TPM_STS_DATA_EXPECT | TPM_STS_VALID,
-			      TPM_STS_DATA_EXPECT | TPM_STS_VALID,
-			      chip->timeout_c, &priv->int_queue, false) < 0) {
-			rc = -EIO;
-			goto out_err;
-		}
 	}
 
-	/* write last byte */
-	rc = tpm_tis_write8(priv, TPM_DATA_FIFO(priv->locality), buf[count]);
-	if (rc < 0)
-		goto out_err;
-
-	if (!itpm && wait_for_tpm_stat
-		     (chip, TPM_STS_DATA_EXPECT | TPM_STS_VALID, TPM_STS_VALID,
-		      chip->timeout_c, &priv->int_queue, false) < 0) {
+	if (!(priv->flags & TPM_TIS_ITPM_WORKAROUND) &&
+	    wait_for_tpm_stat(chip, TPM_STS_DATA_EXPECT | TPM_STS_VALID,
+			      TPM_STS_VALID, chip->timeout_c, &priv->int_queue,
+			      false) < 0) {
 		rc = -EIO;
 		goto out_err;
 	}
-- 
2.7.4