tpm_tis: Use responseRetry to recover from data transfer errors

TPM responses may become damaged during transmission, for example due to
bit flips on the wire. Instead of aborting when detecting such issues, the
responseRetry functionality can be used to make the TPM retransmit its
response and receive it again without errors.

Signed-off-by: Alexander Steffen <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

drivers/char/tpm/tpm_tis_core.c

···
 	return size;
 }
 
-static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
+static int tpm_tis_try_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 {
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
 	int size = 0;
 	int status;
 	u32 expected;
 	int rc;
-
-	if (count < TPM_HEADER_SIZE) {
-		size = -EIO;
-		goto out;
-	}
 
 	size = recv_data(chip, buf, TPM_HEADER_SIZE);
 	/* read first 10 bytes, including tag, paramsize, and result */
···
 		goto out;
 	}
 	status = tpm_tis_status(chip);
-	if (status & TPM_STS_DATA_AVAIL) {	/* retry? */
+	if (status & TPM_STS_DATA_AVAIL) {
 		dev_err(&chip->dev, "Error left over data\n");
 		size = -EIO;
 		goto out;
···
 	}
 
 out:
-	tpm_tis_ready(chip);
 	return size;
+}
+
+static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
+{
+	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
+	unsigned int try;
+	int rc = 0;
+
+	if (count < TPM_HEADER_SIZE)
+		return -EIO;
+
+	for (try = 0; try < TPM_RETRY; try++) {
+		rc = tpm_tis_try_recv(chip, buf, count);
+
+		if (rc == -EIO)
+			/* Data transfer errors, indicated by EIO, can be
+			 * recovered by rereading the response.
+			 */
+			tpm_tis_write8(priv, TPM_STS(priv->locality),
+				       TPM_STS_RESPONSE_RETRY);
+		else
+			break;
+	}
+
+	tpm_tis_ready(chip);
+
+	return rc;
 }
 
 /*

drivers/char/tpm/tpm_tis_core.h

···
 	TPM_STS_GO = 0x20,
 	TPM_STS_DATA_AVAIL = 0x10,
 	TPM_STS_DATA_EXPECT = 0x08,
+	TPM_STS_RESPONSE_RETRY = 0x02,
 	TPM_STS_READ_ZERO = 0x23, /* bits that must be zero on read */
 };