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>

diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
index 639614f2d415a400f118287ed28d2caf17e2742c..62f50b6c9ef69939dcd38faae9df586794cdbdf3 100644 (file)
--- 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;