[PATCH 1/2] tpm: tis_i2c: Limit read bursts to I2C_SMBUS_BLOCK_MAX (32) bytes

["A. Sverdlin" <alexander.sverdlin@xxxxxxxxxxx>]

From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>

Underlying I2C bus drivers not always support longer transfers and
imx-lpi2c for instance doesn't. SLB 9673 offers 427-bytes packets.

Visible symptoms are:

tpm tpm0: Error left over data
tpm tpm0: tpm_transmit: tpm_recv: error -5
tpm_tis_i2c: probe of 1-002e failed with error -5

Fixes: bbc23a07b072 ("tpm: Add tpm_tis_i2c backend for tpm_tis_core")
Tested-by: Michael Haener <michael.haener@xxxxxxxxxxx>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
---
 drivers/char/tpm/tpm_tis_i2c.c | 37 ++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
index c8c34adc14c0..106fd20d94e4 100644
--- a/drivers/char/tpm/tpm_tis_i2c.c
+++ b/drivers/char/tpm/tpm_tis_i2c.c
@@ -189,21 +189,28 @@ static int tpm_tis_i2c_read_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
 	int ret;
 
 	for (i = 0; i < TPM_RETRY; i++) {
-		/* write register */
-		msg.len = sizeof(reg);
-		msg.buf = &reg;
-		msg.flags = 0;
-		ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
-		if (ret < 0)
-			return ret;
-
-		/* read data */
-		msg.buf = result;
-		msg.len = len;
-		msg.flags = I2C_M_RD;
-		ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
-		if (ret < 0)
-			return ret;
+		u16 read = 0;
+
+		while (read < len) {
+			/* write register */
+			msg.len = sizeof(reg);
+			msg.buf = &reg;
+			msg.flags = 0;
+			ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
+			if (ret < 0)
+				return ret;
+
+			/* read data */
+			msg.buf = result + read;
+			msg.len = len - read;
+			msg.flags = I2C_M_RD;
+			if (msg.len > I2C_SMBUS_BLOCK_MAX)
+				msg.len = I2C_SMBUS_BLOCK_MAX;
+			ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
+			if (ret < 0)
+				return ret;
+			read += msg.len;
+		}
 
 		ret = tpm_tis_i2c_sanity_check_read(reg, len, result);
 		if (ret == 0)
-- 
2.40.1