[PATCH 4.9 013/164] tpm_tis_spi: Check correct byte for wait state indicator

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Huewe <peter.huewe@xxxxxxxxxxxx>

commit e110cc69dc2ad679d6d478df636b99b14e6fbbc9 upstream.

Wait states are signaled in the last byte received from the TPM in
response to the header, not the first byte. Check rx_buf[3] instead of
rx_buf[0].

Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
Signed-off-by: Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx>
Signed-off-by: Peter Huewe <peter.huewe@xxxxxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Tested-by: Benoit Houyere <benoit.houyere@xxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/char/tpm/tpm_tis_spi.c |   34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -86,25 +86,25 @@ static int tpm_tis_spi_transfer(struct t
 	if (ret < 0)
 		goto exit;
 
-	phy->tx_buf[0] = 0;
+	if ((phy->rx_buf[3] & 0x01) == 0) {
+		// handle SPI wait states
+		phy->tx_buf[0] = 0;
 
-	/* According to TCG PTP specification, if there is no TPM present at
-	 * all, then the design has a weak pull-up on MISO. If a TPM is not
-	 * present, a pull-up on MISO means that the SB controller sees a 1,
-	 * and will latch in 0xFF on the read.
-	 */
-	for (i = 0; (phy->rx_buf[0] & 0x01) == 0 && i < TPM_RETRY; i++) {
-		spi_xfer.len = 1;
-		spi_message_init(&m);
-		spi_message_add_tail(&spi_xfer, &m);
-		ret = spi_sync_locked(phy->spi_device, &m);
-		if (ret < 0)
-			goto exit;
-	}
+		for (i = 0; i < TPM_RETRY; i++) {
+			spi_xfer.len = 1;
+			spi_message_init(&m);
+			spi_message_add_tail(&spi_xfer, &m);
+			ret = spi_sync_locked(phy->spi_device, &m);
+			if (ret < 0)
+				goto exit;
+			if (phy->rx_buf[0] & 0x01)
+				break;
+		}
 
-	if (i == TPM_RETRY) {
-		ret = -ETIMEDOUT;
-		goto exit;
+		if (i == TPM_RETRY) {
+			ret = -ETIMEDOUT;
+			goto exit;
+		}
 	}
 
 	spi_xfer.cs_change = 0;