tpm_tis_spi: Check correct byte for wait state indicator

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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 b515ce755f12..f0e23011098b 100644
--- 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 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;