tpm_tis_spi: Check correct byte for wait state indicator

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].

Cc: <stable@vger.kernel.org>
Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Signed-off-by: Peter Huewe <peter.huewe@infineon.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Benoit Houyere <benoit.houyere@st.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

1 files changed, 18 insertions, 18 deletions

diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
index 639614f2d415..62f50b6c9ef6 100644
--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -85,25 +85,25 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
         if (ret < 0)
                 goto exit;
 
-        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)
+        if ((phy->rx_buf[3] & 0x01) == 0) {
+                // handle SPI wait states
+                phy->tx_buf[0] = 0;
+
+                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;