[PATCH v2 3/4] tpm_tis: Use responseRetry to recover from data transfer errors

[Alexander Steffen]

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 <Alexander.Steffen@xxxxxxxxxxxx>
---
 drivers/char/tpm/tpm_tis_core.c | 40 ++++++++++++++++++++++++++-------
 drivers/char/tpm/tpm_tis_core.h |  1 +
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 5ddaf24518be..a08768e55803 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -345,11 +345,6 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 	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 */
 	if (size < TPM_HEADER_SIZE) {
@@ -382,7 +377,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 		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;
@@ -396,10 +391,39 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 	}
 
 out:
-	tpm_tis_ready(chip);
 	return size;
 }
 
+static int tpm_tis_recv_with_retries(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) {
+		rc = -EIO;
+		goto out;
+	}
+
+	for (try = 0; try < TPM_RETRY; try++) {
+		rc = tpm_tis_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;
+		}
+	}
+
+out:
+	tpm_tis_ready(chip);
+	return rc;
+}
+
 /*
  * If interrupts are used (signaled by an irq set in the vendor structure)
  * tpm.c can skip polling for the data to be available as the interrupt is
@@ -986,7 +1010,7 @@ static void tpm_tis_clkrun_enable(struct tpm_chip *chip, bool value)
 static const struct tpm_class_ops tpm_tis = {
 	.flags = TPM_OPS_AUTO_STARTUP,
 	.status = tpm_tis_status,
-	.recv = tpm_tis_recv,
+	.recv = tpm_tis_recv_with_retries,
 	.send = tpm_tis_send,
 	.cancel = tpm_tis_ready,
 	.update_timeouts = tpm_tis_update_timeouts,
diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
index e978f457fd4d..8458cd4a84ec 100644
--- a/drivers/char/tpm/tpm_tis_core.h
+++ b/drivers/char/tpm/tpm_tis_core.h
@@ -34,6 +34,7 @@ enum tis_status {
 	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 */
 };
 
-- 
2.34.1