[PATCH v5 0/3] tpm_tis_i2c

[PATCH v5 0/3] tpm_tis_i2c

[Alexander Steffen]

Changelog:
 * v5:
   * Rename tpm_tis-i2c to tpm-tis-i2c
   * Remove unused includes
 * v4:
   * Move changelog to cover letter
   * Add compatibles to trivial-devices.yaml
   * Split patch for CRC interface and implementation
   * Add tpm_tis_i2c prefix to all functions
   * Improve documentation for guard time and sanity check
   * Use for loop instead of while for retries
 * v3:
   * Document address_to_register function
   * Add tpm_tis_i2c prefix to address_to_register
   * Add #ifdef CONFIG_OF to of_tis_i2c_match
   * Fix typos
 * v2:
   * move CCs from copyright comment to commit message
   * fix an unchecked return code

Alexander Steffen (3):
  dt-bindings: trivial-devices: Add two I2C TPM devices
  tpm: Add tpm_tis_verify_crc to the tpm_tis_phy_ops protocol layer
  tpm: Add tpm_tis_i2c backend for tpm_tis_core

 .../devicetree/bindings/trivial-devices.yaml  |   4 +
 drivers/char/tpm/Kconfig                      |  12 +
 drivers/char/tpm/Makefile                     |   1 +
 drivers/char/tpm/tpm_tis_core.c               |  14 +
 drivers/char/tpm/tpm_tis_core.h               |  10 +
 drivers/char/tpm/tpm_tis_i2c.c                | 392 ++++++++++++++++++
 6 files changed, 433 insertions(+)
 create mode 100644 drivers/char/tpm/tpm_tis_i2c.c

-- 
2.25.1

[PATCH v5 1/3] dt-bindings: trivial-devices: Add two I2C TPM devices

[Alexander Steffen]

Both are supported by the upcoming tpm_tis_i2c driver.

Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Change-Id: I4750e39274038715d568d711cde1dc3d8595ba1b
---
 Documentation/devicetree/bindings/trivial-devices.yaml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/trivial-devices.yaml b/Documentation/devicetree/bindings/trivial-devices.yaml
index 6aafa71806a3..92aae2a805f7 100644
--- a/Documentation/devicetree/bindings/trivial-devices.yaml
+++ b/Documentation/devicetree/bindings/trivial-devices.yaml
@@ -139,6 +139,8 @@ properties:
           - infineon,slb9635tt
             # Infineon SLB9645 I2C TPM (new protocol, max 400khz)
           - infineon,slb9645tt
+            # Infineon SLB9673 I2C TPM 2.0
+          - infineon,slb9673
             # Infineon TLV493D-A1B6 I2C 3D Magnetic Sensor
           - infineon,tlv493d-a1b6
             # Infineon Multi-phase Digital VR Controller xdpe11280
@@ -333,6 +335,8 @@ properties:
           - st,24c256
             # Ambient Light Sensor with SMBUS/Two Wire Serial Interface
           - taos,tsl2550
+            # TCG TIS-compliant TPM with I2C interface
+          - tcg,tpm-tis-i2c
             # Temperature Monitoring and Fan Control
           - ti,amc6821
             # Temperature and humidity sensor with i2c interface
-- 
2.25.1

[PATCH v5 2/3] tpm: Add tpm_tis_verify_crc to the tpm_tis_phy_ops protocol layer

[Alexander Steffen]

Some TPMs, e.g. those implementing the I2C variant of TIS, can verify
data transfers to/from the FIFO with a CRC. The CRC is calculated over
the entirety of the FIFO register. Since the phy_ops layer is not aware
when the core layer is done reading/writing the FIFO, CRC verification
must be triggered from the core layer. To this end, add an optional
phy_ops API call.

Co-developed-by: Johannes Holland <johannes.holland@infineon.com>
Signed-off-by: Johannes Holland <johannes.holland@infineon.com>
Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Change-Id: I43716c8d45f62c0fcdaabfc3366f8deb89fd1f32
---
 drivers/char/tpm/tpm_tis_core.c | 14 ++++++++++++++
 drivers/char/tpm/tpm_tis_core.h | 10 ++++++++++
 2 files changed, 24 insertions(+)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index dc56b976d816..757623bacfd5 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -289,6 +289,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 	int size = 0;
 	int status;
 	u32 expected;
+	int rc;
 
 	if (count < TPM_HEADER_SIZE) {
 		size = -EIO;
@@ -328,6 +329,13 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 		goto out;
 	}
 
+	rc = tpm_tis_verify_crc(priv, (size_t)size, buf);
+	if (rc < 0) {
+		dev_err(&chip->dev, "CRC mismatch for response.\n");
+		size = rc;
+		goto out;
+	}
+
 out:
 	tpm_tis_ready(chip);
 	return size;
@@ -443,6 +451,12 @@ static int tpm_tis_send_main(struct tpm_chip *chip, const u8 *buf, size_t len)
 	if (rc < 0)
 		return rc;
 
+	rc = tpm_tis_verify_crc(priv, len, buf);
+	if (rc < 0) {
+		dev_err(&chip->dev, "CRC mismatch for command.\n");
+		return rc;
+	}
+
 	/* go and do it */
 	rc = tpm_tis_write8(priv, TPM_STS(priv->locality), TPM_STS_GO);
 	if (rc < 0)
diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
index 6c203f36b8a1..66a5a13cd1df 100644
--- a/drivers/char/tpm/tpm_tis_core.h
+++ b/drivers/char/tpm/tpm_tis_core.h
@@ -121,6 +121,8 @@ struct tpm_tis_phy_ops {
 			  u8 *result, enum tpm_tis_io_mode mode);
 	int (*write_bytes)(struct tpm_tis_data *data, u32 addr, u16 len,
 			   const u8 *value, enum tpm_tis_io_mode mode);
+	int (*verify_crc)(struct tpm_tis_data *data, size_t len,
+			  const u8 *value);
 };
 
 static inline int tpm_tis_read_bytes(struct tpm_tis_data *data, u32 addr,
@@ -188,6 +190,14 @@ static inline int tpm_tis_write32(struct tpm_tis_data *data, u32 addr,
 	return rc;
 }
 
+static inline int tpm_tis_verify_crc(struct tpm_tis_data *data, size_t len,
+				     const u8 *value)
+{
+	if (!data->phy_ops->verify_crc)
+		return 0;
+	return data->phy_ops->verify_crc(data, len, value);
+}
+
 static inline bool is_bsw(void)
 {
 #ifdef CONFIG_X86
-- 
2.25.1

[PATCH v5 3/3] tpm: Add tpm_tis_i2c backend for tpm_tis_core

[Alexander Steffen]

Implement the TCG I2C Interface driver, as specified in the TCG PC
Client Platform TPM Profile (PTP) specification for TPM 2.0 v1.04
revision 14, section 8, I2C Interface Definition.

This driver supports Guard Times. That is, if required by the TPM, the
driver has to wait by a vendor-specific time after each I2C read/write.
The specific time is read from the TPM_I2C_INTERFACE_CAPABILITY register.

Unfortunately, the TCG specified almost but not quite compatible
register addresses. Therefore, the TIS register addresses need to be
mapped to I2C ones. The locality is stripped because for now, only
locality 0 is supported.

Add a sanity check to I2C reads of e.g. TPM_ACCESS and TPM_STS. This is
to detect communication errors and issues due to non-standard behaviour
(E.g. the clock stretching quirk in the BCM2835, see 4dbfb5f4401f). In
case the sanity check fails, attempt a retry.

Co-developed-by: Johannes Holland <johannes.holland@infineon.com>
Signed-off-by: Johannes Holland <johannes.holland@infineon.com>
Co-developed-by: Amir Mizinski <amirmizi6@gmail.com>
Signed-off-by: Amir Mizinski <amirmizi6@gmail.com>
Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Change-Id: I772a8c3c487dfdb59337a73eb0e954a048c5df21
---
 drivers/char/tpm/Kconfig       |  12 +
 drivers/char/tpm/Makefile      |   1 +
 drivers/char/tpm/tpm_tis_i2c.c | 392 +++++++++++++++++++++++++++++++++
 3 files changed, 405 insertions(+)
 create mode 100644 drivers/char/tpm/tpm_tis_i2c.c

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 4a5516406c22..927088b2c3d3 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -74,6 +74,18 @@ config TCG_TIS_SPI_CR50
 	  If you have a H1 secure module running Cr50 firmware on SPI bus,
 	  say Yes and it will be accessible from within Linux.
 
+config TCG_TIS_I2C
+	tristate "TPM Interface Specification 1.3 Interface / TPM 2.0 FIFO Interface - (I2C - generic)"
+	depends on I2C
+	select CRC_CCITT
+	select TCG_TIS_CORE
+	help
+	  If you have a TPM security chip, compliant with the TCG TPM PTP
+	  (I2C interface) specification and connected to an I2C bus master,
+	  say Yes and it will be accessible from within Linux.
+	  To compile this driver as a module, choose M here;
+	  the module will be called tpm_tis_i2c.
+
 config TCG_TIS_SYNQUACER
 	tristate "TPM Interface Specification 1.2 Interface / TPM 2.0 FIFO Interface (MMIO - SynQuacer)"
 	depends on ARCH_SYNQUACER || COMPILE_TEST
diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
index 66d39ea6bd10..0222b1ddb310 100644
--- a/drivers/char/tpm/Makefile
+++ b/drivers/char/tpm/Makefile
@@ -29,6 +29,7 @@ tpm_tis_spi-$(CONFIG_TCG_TIS_SPI_CR50) += tpm_tis_spi_cr50.o
 
 obj-$(CONFIG_TCG_TIS_I2C_CR50) += tpm_tis_i2c_cr50.o
 
+obj-$(CONFIG_TCG_TIS_I2C) += tpm_tis_i2c.o
 obj-$(CONFIG_TCG_TIS_I2C_ATMEL) += tpm_i2c_atmel.o
 obj-$(CONFIG_TCG_TIS_I2C_INFINEON) += tpm_i2c_infineon.o
 obj-$(CONFIG_TCG_TIS_I2C_NUVOTON) += tpm_i2c_nuvoton.o
diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
new file mode 100644
index 000000000000..6119bf78b36c
--- /dev/null
+++ b/drivers/char/tpm/tpm_tis_i2c.c
@@ -0,0 +1,392 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2014-2021 Nuvoton Technology corporation
+ * Copyright (C) 2019-2022 Infineon Technologies AG
+ *
+ * This device driver implements the TPM interface as defined in the TCG PC
+ * Client Platform TPM Profile (PTP) Specification for TPM 2.0 v1.04
+ * Revision 14.
+ *
+ * It is based on the tpm_tis_spi device driver.
+ */
+
+#include <linux/i2c.h>
+#include <linux/crc-ccitt.h>
+#include "tpm_tis_core.h"
+
+/* TPM registers */
+#define TPM_I2C_LOC_SEL 0x00
+#define TPM_I2C_ACCESS 0x04
+#define TPM_I2C_INTERFACE_CAPABILITY 0x30
+#define TPM_I2C_DEVICE_ADDRESS 0x38
+#define TPM_I2C_DATA_CSUM_ENABLE 0x40
+#define TPM_DATA_CSUM 0x44
+#define TPM_I2C_DID_VID 0x48
+#define TPM_I2C_RID 0x4C
+
+/* TIS-compatible register address to avoid clash with TPM_ACCESS (0x00) */
+#define TPM_LOC_SEL 0x0FFF
+
+/* Mask to extract the I2C register from TIS register addresses */
+#define TPM_TIS_REGISTER_MASK 0x0FFF
+
+/* Default Guard Time of 250µs until interface capability register is read */
+#define GUARD_TIME_DEFAULT_MIN 250
+#define GUARD_TIME_DEFAULT_MAX 300
+
+/* Guard Time of 250µs after I2C slave NACK */
+#define GUARD_TIME_ERR_MIN 250
+#define GUARD_TIME_ERR_MAX 300
+
+/* Guard Time bit masks; SR is repeated start, RW is read then write, etc. */
+#define TPM_GUARD_TIME_SR_MASK 0x40000000
+#define TPM_GUARD_TIME_RR_MASK 0x00100000
+#define TPM_GUARD_TIME_RW_MASK 0x00080000
+#define TPM_GUARD_TIME_WR_MASK 0x00040000
+#define TPM_GUARD_TIME_WW_MASK 0x00020000
+#define TPM_GUARD_TIME_MIN_MASK 0x0001FE00
+#define TPM_GUARD_TIME_MIN_SHIFT 9
+
+/* Masks with bits that must be read zero */
+#define TPM_ACCESS_READ_ZERO 0x48
+#define TPM_INT_ENABLE_ZERO 0x7FFFFF6
+#define TPM_STS_READ_ZERO 0x23
+#define TPM_INTF_CAPABILITY_ZERO 0x0FFFF000
+#define TPM_I2C_INTERFACE_CAPABILITY_ZERO 0x80000000
+
+struct tpm_tis_i2c_phy {
+	struct tpm_tis_data priv;
+	struct i2c_client *i2c_client;
+	bool guard_time_read;
+	bool guard_time_write;
+	u16 guard_time_min;
+	u16 guard_time_max;
+	u8 *io_buf;
+};
+
+static inline struct tpm_tis_i2c_phy *
+to_tpm_tis_i2c_phy(struct tpm_tis_data *data)
+{
+	return container_of(data, struct tpm_tis_i2c_phy, priv);
+}
+
+/*
+ * tpm_tis_core uses the register addresses as defined in Table 19 "Allocation
+ * of Register Space for FIFO TPM Access" of the TCG PC Client PTP
+ * Specification. In order for this code to work together with tpm_tis_core,
+ * those addresses need to mapped to the registers defined for I2C TPMs in
+ * Table 51 "I2C-TPM Register Overview".
+ *
+ * For most addresses this can be done by simply stripping off the locality
+ * information from the address. A few addresses need to be mapped explicitly,
+ * since the corresponding I2C registers have been moved around. TPM_LOC_SEL is
+ * only defined for I2C TPMs and is also mapped explicitly here to distinguish
+ * it from TPM_ACCESS(0).
+ *
+ * Locality information is ignored, since this driver assumes exclusive access
+ * to the TPM and always uses locality 0.
+ */
+static u8 tpm_tis_i2c_address_to_register(u32 addr)
+{
+	addr &= TPM_TIS_REGISTER_MASK;
+
+	switch (addr) {
+	case TPM_ACCESS(0):
+		return TPM_I2C_ACCESS;
+	case TPM_LOC_SEL:
+		return TPM_I2C_LOC_SEL;
+	case TPM_DID_VID(0):
+		return TPM_I2C_DID_VID;
+	case TPM_RID(0):
+		return TPM_I2C_RID;
+	default:
+		return addr;
+	}
+}
+
+static int tpm_tis_i2c_retry_transfer_until_ack(struct tpm_tis_data *data,
+						struct i2c_msg *msg)
+{
+	struct tpm_tis_i2c_phy *phy = to_tpm_tis_i2c_phy(data);
+	bool guard_time;
+	int i = 0;
+	int ret;
+
+	if (msg->flags & I2C_M_RD)
+		guard_time = phy->guard_time_read;
+	else
+		guard_time = phy->guard_time_write;
+
+	do {
+		ret = i2c_transfer(phy->i2c_client->adapter, msg, 1);
+		if (ret < 0)
+			usleep_range(GUARD_TIME_ERR_MIN, GUARD_TIME_ERR_MAX);
+		else if (guard_time)
+			usleep_range(phy->guard_time_min, phy->guard_time_max);
+		/* retry on TPM NACK */
+	} while (ret < 0 && i++ < TPM_RETRY);
+
+	return ret;
+}
+
+/* Check that bits which must be read zero are not set */
+static int tpm_tis_i2c_sanity_check_read(u8 reg, u16 len, u8 *buf)
+{
+	u32 zero_mask;
+	u32 value;
+
+	switch (len) {
+	case sizeof(u8):
+		value = buf[0];
+		break;
+	case sizeof(u16):
+		value = le16_to_cpup((__le16 *)buf);
+		break;
+	case sizeof(u32):
+		value = le32_to_cpup((__le32 *)buf);
+		break;
+	default:
+		/* unknown length, skip check */
+		return 0;
+	}
+
+	switch (reg) {
+	case TPM_I2C_ACCESS:
+		zero_mask = TPM_ACCESS_READ_ZERO;
+		break;
+	case TPM_INT_ENABLE(0) & TPM_TIS_REGISTER_MASK:
+		zero_mask = TPM_INT_ENABLE_ZERO;
+		break;
+	case TPM_STS(0) & TPM_TIS_REGISTER_MASK:
+		zero_mask = TPM_STS_READ_ZERO;
+		break;
+	case TPM_INTF_CAPS(0) & TPM_TIS_REGISTER_MASK:
+		zero_mask = TPM_INTF_CAPABILITY_ZERO;
+		break;
+	case TPM_I2C_INTERFACE_CAPABILITY:
+		zero_mask = TPM_I2C_INTERFACE_CAPABILITY_ZERO;
+		break;
+	default:
+		/* unknown register, skip check */
+		return 0;
+	}
+
+	if (unlikely((value & zero_mask) != 0x00)) {
+		pr_debug("TPM I2C read of register 0x%02x failed sanity check: 0x%x\n", reg, value);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int tpm_tis_i2c_read_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
+				  u8 *result, enum tpm_tis_io_mode io_mode)
+{
+	struct tpm_tis_i2c_phy *phy = to_tpm_tis_i2c_phy(data);
+	struct i2c_msg msg = { .addr = phy->i2c_client->addr };
+	u8 reg = tpm_tis_i2c_address_to_register(addr);
+	int i;
+	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;
+
+		ret = tpm_tis_i2c_sanity_check_read(reg, len, result);
+		if (ret == 0)
+			return 0;
+
+		usleep_range(GUARD_TIME_ERR_MIN, GUARD_TIME_ERR_MAX);
+	}
+
+	return ret;
+}
+
+static int tpm_tis_i2c_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
+				   const u8 *value,
+				   enum tpm_tis_io_mode io_mode)
+{
+	struct tpm_tis_i2c_phy *phy = to_tpm_tis_i2c_phy(data);
+	struct i2c_msg msg = { .addr = phy->i2c_client->addr };
+	u8 reg = tpm_tis_i2c_address_to_register(addr);
+	int ret;
+
+	if (len > TPM_BUFSIZE - 1)
+		return -EIO;
+
+	/* write register and data in one go */
+	phy->io_buf[0] = reg;
+	memcpy(phy->io_buf + sizeof(reg), value, len);
+
+	msg.len = sizeof(reg) + len;
+	msg.buf = phy->io_buf;
+	ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int tpm_tis_i2c_verify_crc(struct tpm_tis_data *data, size_t len,
+				  const u8 *value)
+{
+	u16 crc_tpm, crc_host;
+	int rc;
+
+	rc = tpm_tis_read16(data, TPM_DATA_CSUM, &crc_tpm);
+	if (rc < 0)
+		return rc;
+
+	/* reflect crc result, regardless of host endianness */
+	crc_host = swab16(crc_ccitt(0, value, len));
+	if (crc_tpm != crc_host)
+		return -EIO;
+
+	return 0;
+}
+
+/*
+ * Guard Time:
+ * After each I2C operation, the TPM might require the master to wait.
+ * The time period is vendor-specific and must be read from the
+ * TPM_I2C_INTERFACE_CAPABILITY register.
+ *
+ * Before the Guard Time is read (or after the TPM failed to send an I2C NACK),
+ * a Guard Time of 250µs applies.
+ *
+ * Various flags in the same register indicate if a guard time is needed:
+ *  - SR: <I2C read with repeated start> <guard time> <I2C read>
+ *  - RR: <I2C read> <guard time> <I2C read>
+ *  - RW: <I2C read> <guard time> <I2C write>
+ *  - WR: <I2C write> <guard time> <I2C read>
+ *  - WW: <I2C write> <guard time> <I2C write>
+ *
+ * See TCG PC Client PTP Specification v1.04, 8.1.10 GUARD_TIME
+ */
+static int tpm_tis_i2c_init_guard_time(struct tpm_tis_i2c_phy *phy)
+{
+	u32 i2c_caps;
+	int ret;
+
+	phy->guard_time_read = true;
+	phy->guard_time_write = true;
+	phy->guard_time_min = GUARD_TIME_DEFAULT_MIN;
+	phy->guard_time_max = GUARD_TIME_DEFAULT_MAX;
+
+	ret = tpm_tis_i2c_read_bytes(&phy->priv, TPM_I2C_INTERFACE_CAPABILITY,
+				     sizeof(i2c_caps), (u8 *)&i2c_caps,
+				     TPM_TIS_PHYS_32);
+	if (ret)
+		return ret;
+
+	phy->guard_time_read = (i2c_caps & TPM_GUARD_TIME_RR_MASK) ||
+			       (i2c_caps & TPM_GUARD_TIME_RW_MASK);
+	phy->guard_time_write = (i2c_caps & TPM_GUARD_TIME_WR_MASK) ||
+				(i2c_caps & TPM_GUARD_TIME_WW_MASK);
+	phy->guard_time_min = (i2c_caps & TPM_GUARD_TIME_MIN_MASK) >>
+			      TPM_GUARD_TIME_MIN_SHIFT;
+	/* guard_time_max = guard_time_min * 1.2 */
+	phy->guard_time_max = phy->guard_time_min + phy->guard_time_min / 5;
+
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(tpm_tis_pm, tpm_pm_suspend, tpm_tis_resume);
+
+static const struct tpm_tis_phy_ops tpm_i2c_phy_ops = {
+	.read_bytes = tpm_tis_i2c_read_bytes,
+	.write_bytes = tpm_tis_i2c_write_bytes,
+	.verify_crc = tpm_tis_i2c_verify_crc,
+};
+
+static int tpm_tis_i2c_probe(struct i2c_client *dev,
+			     const struct i2c_device_id *id)
+{
+	struct tpm_tis_i2c_phy *phy;
+	const u8 crc_enable = 1;
+	const u8 locality = 0;
+	int ret;
+
+	phy = devm_kzalloc(&dev->dev, sizeof(struct tpm_tis_i2c_phy),
+			   GFP_KERNEL);
+	if (!phy)
+		return -ENOMEM;
+
+	phy->io_buf = devm_kzalloc(&dev->dev, TPM_BUFSIZE, GFP_KERNEL);
+	if (!phy->io_buf)
+		return -ENOMEM;
+
+	phy->i2c_client = dev;
+
+	/* must precede all communication with the tpm */
+	ret = tpm_tis_i2c_init_guard_time(phy);
+	if (ret)
+		return ret;
+
+	ret = tpm_tis_i2c_write_bytes(&phy->priv, TPM_LOC_SEL, sizeof(locality),
+				      &locality, TPM_TIS_PHYS_8);
+	if (ret)
+		return ret;
+
+	ret = tpm_tis_i2c_write_bytes(&phy->priv, TPM_I2C_DATA_CSUM_ENABLE,
+				      sizeof(crc_enable), &crc_enable,
+				      TPM_TIS_PHYS_8);
+	if (ret)
+		return ret;
+
+	return tpm_tis_core_init(&dev->dev, &phy->priv, -1, &tpm_i2c_phy_ops,
+				 NULL);
+}
+
+static int tpm_tis_i2c_remove(struct i2c_client *client)
+{
+	struct tpm_chip *chip = i2c_get_clientdata(client);
+
+	tpm_chip_unregister(chip);
+	tpm_tis_remove(chip);
+	return 0;
+}
+
+static const struct i2c_device_id tpm_tis_i2c_id[] = {
+	{ "tpm_tis_i2c", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, tpm_tis_i2c_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id of_tis_i2c_match[] = {
+	{ .compatible = "infineon,slb9673", },
+	{ .compatible = "tcg,tpm-tis-i2c", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, of_tis_i2c_match);
+#endif
+
+static struct i2c_driver tpm_tis_i2c_driver = {
+	.driver = {
+		.owner = THIS_MODULE,
+		.name = "tpm_tis_i2c",
+		.pm = &tpm_tis_pm,
+		.of_match_table = of_match_ptr(of_tis_i2c_match),
+	},
+	.probe = tpm_tis_i2c_probe,
+	.remove = tpm_tis_i2c_remove,
+	.id_table = tpm_tis_i2c_id,
+};
+module_i2c_driver(tpm_tis_i2c_driver);
+
+MODULE_DESCRIPTION("TPM Driver for native I2C access");
+MODULE_LICENSE("GPL");
-- 
2.25.1

Re: [PATCH v5 1/3] dt-bindings: trivial-devices: Add two I2C TPM devices

[Rob Herring]

On Fri, Jun 03, 2022 at 04:35:30PM +0200, Alexander Steffen wrote:
> Both are supported by the upcoming tpm_tis_i2c driver.
> 
> Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
> Change-Id: I4750e39274038715d568d711cde1dc3d8595ba1b
> ---
>  Documentation/devicetree/bindings/trivial-devices.yaml | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/trivial-devices.yaml b/Documentation/devicetree/bindings/trivial-devices.yaml
> index 6aafa71806a3..92aae2a805f7 100644
> --- a/Documentation/devicetree/bindings/trivial-devices.yaml
> +++ b/Documentation/devicetree/bindings/trivial-devices.yaml
> @@ -139,6 +139,8 @@ properties:
>            - infineon,slb9635tt
>              # Infineon SLB9645 I2C TPM (new protocol, max 400khz)
>            - infineon,slb9645tt
> +            # Infineon SLB9673 I2C TPM 2.0
> +          - infineon,slb9673
>              # Infineon TLV493D-A1B6 I2C 3D Magnetic Sensor
>            - infineon,tlv493d-a1b6
>              # Infineon Multi-phase Digital VR Controller xdpe11280
> @@ -333,6 +335,8 @@ properties:
>            - st,24c256
>              # Ambient Light Sensor with SMBUS/Two Wire Serial Interface
>            - taos,tsl2550
> +            # TCG TIS-compliant TPM with I2C interface
> +          - tcg,tpm-tis-i2c

Again, not a trivial device.

>              # Temperature Monitoring and Fan Control
>            - ti,amc6821
>              # Temperature and humidity sensor with i2c interface
> -- 
> 2.25.1
> 
> 

Re: [PATCH v5 2/3] tpm: Add tpm_tis_verify_crc to the tpm_tis_phy_ops protocol layer

[Jarkko Sakkinen]

On Fri, Jun 03, 2022 at 04:35:31PM +0200, Alexander Steffen wrote:
> Some TPMs, e.g. those implementing the I2C variant of TIS, can verify
> data transfers to/from the FIFO with a CRC. The CRC is calculated over
> the entirety of the FIFO register. Since the phy_ops layer is not aware
> when the core layer is done reading/writing the FIFO, CRC verification
> must be triggered from the core layer. To this end, add an optional
> phy_ops API call.
> 
> Co-developed-by: Johannes Holland <johannes.holland@infineon.com>
> Signed-off-by: Johannes Holland <johannes.holland@infineon.com>
> Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
> Change-Id: I43716c8d45f62c0fcdaabfc3366f8deb89fd1f32

Strip off Change-Id.

> ---
>  drivers/char/tpm/tpm_tis_core.c | 14 ++++++++++++++
>  drivers/char/tpm/tpm_tis_core.h | 10 ++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index dc56b976d816..757623bacfd5 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -289,6 +289,7 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  	int size = 0;
>  	int status;
>  	u32 expected;
> +	int rc;
>  
>  	if (count < TPM_HEADER_SIZE) {
>  		size = -EIO;
> @@ -328,6 +329,13 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  		goto out;
>  	}
>  
> +	rc = tpm_tis_verify_crc(priv, (size_t)size, buf);
> +	if (rc < 0) {
> +		dev_err(&chip->dev, "CRC mismatch for response.\n");
> +		size = rc;
> +		goto out;
> +	}
> +
>  out:
>  	tpm_tis_ready(chip);
>  	return size;
> @@ -443,6 +451,12 @@ static int tpm_tis_send_main(struct tpm_chip *chip, const u8 *buf, size_t len)
>  	if (rc < 0)
>  		return rc;
>  
> +	rc = tpm_tis_verify_crc(priv, len, buf);
> +	if (rc < 0) {
> +		dev_err(&chip->dev, "CRC mismatch for command.\n");
> +		return rc;
> +	}
> +
>  	/* go and do it */
>  	rc = tpm_tis_write8(priv, TPM_STS(priv->locality), TPM_STS_GO);
>  	if (rc < 0)
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 6c203f36b8a1..66a5a13cd1df 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -121,6 +121,8 @@ struct tpm_tis_phy_ops {
>  			  u8 *result, enum tpm_tis_io_mode mode);
>  	int (*write_bytes)(struct tpm_tis_data *data, u32 addr, u16 len,
>  			   const u8 *value, enum tpm_tis_io_mode mode);
> +	int (*verify_crc)(struct tpm_tis_data *data, size_t len,
> +			  const u8 *value);
>  };
>  
>  static inline int tpm_tis_read_bytes(struct tpm_tis_data *data, u32 addr,
> @@ -188,6 +190,14 @@ static inline int tpm_tis_write32(struct tpm_tis_data *data, u32 addr,
>  	return rc;
>  }
>  
> +static inline int tpm_tis_verify_crc(struct tpm_tis_data *data, size_t len,
> +				     const u8 *value)
> +{
> +	if (!data->phy_ops->verify_crc)
> +		return 0;

I think it would be more readable to have one empty line here.

> +	return data->phy_ops->verify_crc(data, len, value);
> +}
> +
>  static inline bool is_bsw(void)
>  {
>  #ifdef CONFIG_X86
> -- 
> 2.25.1
> 

Other than that LGTM.

BR, Jarkko

Re: [PATCH v5 3/3] tpm: Add tpm_tis_i2c backend for tpm_tis_core

[Jarkko Sakkinen]

On Fri, Jun 03, 2022 at 04:35:32PM +0200, Alexander Steffen wrote:
> Implement the TCG I2C Interface driver, as specified in the TCG PC
> Client Platform TPM Profile (PTP) specification for TPM 2.0 v1.04
> revision 14, section 8, I2C Interface Definition.
> 
> This driver supports Guard Times. That is, if required by the TPM, the
> driver has to wait by a vendor-specific time after each I2C read/write.
> The specific time is read from the TPM_I2C_INTERFACE_CAPABILITY register.
> 
> Unfortunately, the TCG specified almost but not quite compatible
> register addresses. Therefore, the TIS register addresses need to be
> mapped to I2C ones. The locality is stripped because for now, only
> locality 0 is supported.
> 
> Add a sanity check to I2C reads of e.g. TPM_ACCESS and TPM_STS. This is
> to detect communication errors and issues due to non-standard behaviour
> (E.g. the clock stretching quirk in the BCM2835, see 4dbfb5f4401f). In
> case the sanity check fails, attempt a retry.
> 
> Co-developed-by: Johannes Holland <johannes.holland@infineon.com>
> Signed-off-by: Johannes Holland <johannes.holland@infineon.com>
> Co-developed-by: Amir Mizinski <amirmizi6@gmail.com>
> Signed-off-by: Amir Mizinski <amirmizi6@gmail.com>
> Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
> Change-Id: I772a8c3c487dfdb59337a73eb0e954a048c5df21

Strip off Change-ID.

> ---
>  drivers/char/tpm/Kconfig       |  12 +
>  drivers/char/tpm/Makefile      |   1 +
>  drivers/char/tpm/tpm_tis_i2c.c | 392 +++++++++++++++++++++++++++++++++
>  3 files changed, 405 insertions(+)
>  create mode 100644 drivers/char/tpm/tpm_tis_i2c.c
> 
> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index 4a5516406c22..927088b2c3d3 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -74,6 +74,18 @@ config TCG_TIS_SPI_CR50
>  	  If you have a H1 secure module running Cr50 firmware on SPI bus,
>  	  say Yes and it will be accessible from within Linux.
>  
> +config TCG_TIS_I2C
> +	tristate "TPM Interface Specification 1.3 Interface / TPM 2.0 FIFO Interface - (I2C - generic)"
> +	depends on I2C
> +	select CRC_CCITT
> +	select TCG_TIS_CORE
> +	help
> +	  If you have a TPM security chip, compliant with the TCG TPM PTP
> +	  (I2C interface) specification and connected to an I2C bus master,
> +	  say Yes and it will be accessible from within Linux.
> +	  To compile this driver as a module, choose M here;
> +	  the module will be called tpm_tis_i2c.
> +
>  config TCG_TIS_SYNQUACER
>  	tristate "TPM Interface Specification 1.2 Interface / TPM 2.0 FIFO Interface (MMIO - SynQuacer)"
>  	depends on ARCH_SYNQUACER || COMPILE_TEST
> diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
> index 66d39ea6bd10..0222b1ddb310 100644
> --- a/drivers/char/tpm/Makefile
> +++ b/drivers/char/tpm/Makefile
> @@ -29,6 +29,7 @@ tpm_tis_spi-$(CONFIG_TCG_TIS_SPI_CR50) += tpm_tis_spi_cr50.o
>  
>  obj-$(CONFIG_TCG_TIS_I2C_CR50) += tpm_tis_i2c_cr50.o
>  
> +obj-$(CONFIG_TCG_TIS_I2C) += tpm_tis_i2c.o
>  obj-$(CONFIG_TCG_TIS_I2C_ATMEL) += tpm_i2c_atmel.o
>  obj-$(CONFIG_TCG_TIS_I2C_INFINEON) += tpm_i2c_infineon.o
>  obj-$(CONFIG_TCG_TIS_I2C_NUVOTON) += tpm_i2c_nuvoton.o
> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> new file mode 100644
> index 000000000000..6119bf78b36c
> --- /dev/null
> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> @@ -0,0 +1,392 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2014-2021 Nuvoton Technology corporation
> + * Copyright (C) 2019-2022 Infineon Technologies AG
> + *
> + * This device driver implements the TPM interface as defined in the TCG PC
> + * Client Platform TPM Profile (PTP) Specification for TPM 2.0 v1.04
> + * Revision 14.
> + *
> + * It is based on the tpm_tis_spi device driver.
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/crc-ccitt.h>
> +#include "tpm_tis_core.h"
> +
> +/* TPM registers */
> +#define TPM_I2C_LOC_SEL 0x00
> +#define TPM_I2C_ACCESS 0x04
> +#define TPM_I2C_INTERFACE_CAPABILITY 0x30
> +#define TPM_I2C_DEVICE_ADDRESS 0x38
> +#define TPM_I2C_DATA_CSUM_ENABLE 0x40
> +#define TPM_DATA_CSUM 0x44
> +#define TPM_I2C_DID_VID 0x48
> +#define TPM_I2C_RID 0x4C
> +
> +/* TIS-compatible register address to avoid clash with TPM_ACCESS (0x00) */
> +#define TPM_LOC_SEL 0x0FFF
> +
> +/* Mask to extract the I2C register from TIS register addresses */
> +#define TPM_TIS_REGISTER_MASK 0x0FFF
> +
> +/* Default Guard Time of 250µs until interface capability register is read */

Please use "us" instead.

> +#define GUARD_TIME_DEFAULT_MIN 250
> +#define GUARD_TIME_DEFAULT_MAX 300
> +
> +/* Guard Time of 250µs after I2C slave NACK */

Ditto.

> +#define GUARD_TIME_ERR_MIN 250
> +#define GUARD_TIME_ERR_MAX 300
> +
> +/* Guard Time bit masks; SR is repeated start, RW is read then write, etc. */
> +#define TPM_GUARD_TIME_SR_MASK 0x40000000
> +#define TPM_GUARD_TIME_RR_MASK 0x00100000
> +#define TPM_GUARD_TIME_RW_MASK 0x00080000
> +#define TPM_GUARD_TIME_WR_MASK 0x00040000
> +#define TPM_GUARD_TIME_WW_MASK 0x00020000
> +#define TPM_GUARD_TIME_MIN_MASK 0x0001FE00
> +#define TPM_GUARD_TIME_MIN_SHIFT 9
> +
> +/* Masks with bits that must be read zero */
> +#define TPM_ACCESS_READ_ZERO 0x48
> +#define TPM_INT_ENABLE_ZERO 0x7FFFFF6
> +#define TPM_STS_READ_ZERO 0x23
> +#define TPM_INTF_CAPABILITY_ZERO 0x0FFFF000
> +#define TPM_I2C_INTERFACE_CAPABILITY_ZERO 0x80000000
> +
> +struct tpm_tis_i2c_phy {
> +	struct tpm_tis_data priv;
> +	struct i2c_client *i2c_client;
> +	bool guard_time_read;
> +	bool guard_time_write;
> +	u16 guard_time_min;
> +	u16 guard_time_max;
> +	u8 *io_buf;
> +};
> +
> +static inline struct tpm_tis_i2c_phy *
> +to_tpm_tis_i2c_phy(struct tpm_tis_data *data)
> +{
> +	return container_of(data, struct tpm_tis_i2c_phy, priv);
> +}
> +
> +/*
> + * tpm_tis_core uses the register addresses as defined in Table 19 "Allocation
> + * of Register Space for FIFO TPM Access" of the TCG PC Client PTP
> + * Specification. In order for this code to work together with tpm_tis_core,
> + * those addresses need to mapped to the registers defined for I2C TPMs in
> + * Table 51 "I2C-TPM Register Overview".
> + *
> + * For most addresses this can be done by simply stripping off the locality
> + * information from the address. A few addresses need to be mapped explicitly,
> + * since the corresponding I2C registers have been moved around. TPM_LOC_SEL is
> + * only defined for I2C TPMs and is also mapped explicitly here to distinguish
> + * it from TPM_ACCESS(0).
> + *
> + * Locality information is ignored, since this driver assumes exclusive access
> + * to the TPM and always uses locality 0.
> + */
> +static u8 tpm_tis_i2c_address_to_register(u32 addr)
> +{
> +	addr &= TPM_TIS_REGISTER_MASK;
> +
> +	switch (addr) {
> +	case TPM_ACCESS(0):
> +		return TPM_I2C_ACCESS;
> +	case TPM_LOC_SEL:
> +		return TPM_I2C_LOC_SEL;
> +	case TPM_DID_VID(0):
> +		return TPM_I2C_DID_VID;
> +	case TPM_RID(0):
> +		return TPM_I2C_RID;
> +	default:
> +		return addr;
> +	}
> +}
> +
> +static int tpm_tis_i2c_retry_transfer_until_ack(struct tpm_tis_data *data,
> +						struct i2c_msg *msg)
> +{
> +	struct tpm_tis_i2c_phy *phy = to_tpm_tis_i2c_phy(data);
> +	bool guard_time;
> +	int i = 0;
> +	int ret;
> +
> +	if (msg->flags & I2C_M_RD)
> +		guard_time = phy->guard_time_read;
> +	else
> +		guard_time = phy->guard_time_write;
> +
> +	do {
> +		ret = i2c_transfer(phy->i2c_client->adapter, msg, 1);
> +		if (ret < 0)
> +			usleep_range(GUARD_TIME_ERR_MIN, GUARD_TIME_ERR_MAX);
> +		else if (guard_time)
> +			usleep_range(phy->guard_time_min, phy->guard_time_max);
> +		/* retry on TPM NACK */
> +	} while (ret < 0 && i++ < TPM_RETRY);
> +
> +	return ret;
> +}
> +
> +/* Check that bits which must be read zero are not set */
> +static int tpm_tis_i2c_sanity_check_read(u8 reg, u16 len, u8 *buf)
> +{
> +	u32 zero_mask;
> +	u32 value;
> +
> +	switch (len) {
> +	case sizeof(u8):
> +		value = buf[0];
> +		break;
> +	case sizeof(u16):
> +		value = le16_to_cpup((__le16 *)buf);
> +		break;
> +	case sizeof(u32):
> +		value = le32_to_cpup((__le32 *)buf);
> +		break;
> +	default:
> +		/* unknown length, skip check */
> +		return 0;
> +	}
> +
> +	switch (reg) {
> +	case TPM_I2C_ACCESS:
> +		zero_mask = TPM_ACCESS_READ_ZERO;
> +		break;
> +	case TPM_INT_ENABLE(0) & TPM_TIS_REGISTER_MASK:
> +		zero_mask = TPM_INT_ENABLE_ZERO;
> +		break;
> +	case TPM_STS(0) & TPM_TIS_REGISTER_MASK:
> +		zero_mask = TPM_STS_READ_ZERO;
> +		break;
> +	case TPM_INTF_CAPS(0) & TPM_TIS_REGISTER_MASK:
> +		zero_mask = TPM_INTF_CAPABILITY_ZERO;
> +		break;
> +	case TPM_I2C_INTERFACE_CAPABILITY:
> +		zero_mask = TPM_I2C_INTERFACE_CAPABILITY_ZERO;
> +		break;
> +	default:
> +		/* unknown register, skip check */
> +		return 0;
> +	}
> +
> +	if (unlikely((value & zero_mask) != 0x00)) {
> +		pr_debug("TPM I2C read of register 0x%02x failed sanity check: 0x%x\n", reg, value);
> +		return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +static int tpm_tis_i2c_read_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
> +				  u8 *result, enum tpm_tis_io_mode io_mode)
> +{
> +	struct tpm_tis_i2c_phy *phy = to_tpm_tis_i2c_phy(data);
> +	struct i2c_msg msg = { .addr = phy->i2c_client->addr };
> +	u8 reg = tpm_tis_i2c_address_to_register(addr);
> +	int i;
> +	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;
> +
> +		ret = tpm_tis_i2c_sanity_check_read(reg, len, result);
> +		if (ret == 0)
> +			return 0;
> +
> +		usleep_range(GUARD_TIME_ERR_MIN, GUARD_TIME_ERR_MAX);
> +	}
> +
> +	return ret;
> +}
> +
> +static int tpm_tis_i2c_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
> +				   const u8 *value,
> +				   enum tpm_tis_io_mode io_mode)
> +{
> +	struct tpm_tis_i2c_phy *phy = to_tpm_tis_i2c_phy(data);
> +	struct i2c_msg msg = { .addr = phy->i2c_client->addr };
> +	u8 reg = tpm_tis_i2c_address_to_register(addr);
> +	int ret;
> +
> +	if (len > TPM_BUFSIZE - 1)
> +		return -EIO;
> +
> +	/* write register and data in one go */
> +	phy->io_buf[0] = reg;
> +	memcpy(phy->io_buf + sizeof(reg), value, len);
> +
> +	msg.len = sizeof(reg) + len;
> +	msg.buf = phy->io_buf;
> +	ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int tpm_tis_i2c_verify_crc(struct tpm_tis_data *data, size_t len,
> +				  const u8 *value)
> +{
> +	u16 crc_tpm, crc_host;
> +	int rc;
> +
> +	rc = tpm_tis_read16(data, TPM_DATA_CSUM, &crc_tpm);
> +	if (rc < 0)
> +		return rc;
> +
> +	/* reflect crc result, regardless of host endianness */
> +	crc_host = swab16(crc_ccitt(0, value, len));
> +	if (crc_tpm != crc_host)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +/*
> + * Guard Time:
> + * After each I2C operation, the TPM might require the master to wait.
> + * The time period is vendor-specific and must be read from the
> + * TPM_I2C_INTERFACE_CAPABILITY register.
> + *
> + * Before the Guard Time is read (or after the TPM failed to send an I2C NACK),
> + * a Guard Time of 250µs applies.
> + *
> + * Various flags in the same register indicate if a guard time is needed:
> + *  - SR: <I2C read with repeated start> <guard time> <I2C read>
> + *  - RR: <I2C read> <guard time> <I2C read>
> + *  - RW: <I2C read> <guard time> <I2C write>
> + *  - WR: <I2C write> <guard time> <I2C read>
> + *  - WW: <I2C write> <guard time> <I2C write>
> + *
> + * See TCG PC Client PTP Specification v1.04, 8.1.10 GUARD_TIME
> + */
> +static int tpm_tis_i2c_init_guard_time(struct tpm_tis_i2c_phy *phy)
> +{
> +	u32 i2c_caps;
> +	int ret;
> +
> +	phy->guard_time_read = true;
> +	phy->guard_time_write = true;
> +	phy->guard_time_min = GUARD_TIME_DEFAULT_MIN;
> +	phy->guard_time_max = GUARD_TIME_DEFAULT_MAX;
> +
> +	ret = tpm_tis_i2c_read_bytes(&phy->priv, TPM_I2C_INTERFACE_CAPABILITY,
> +				     sizeof(i2c_caps), (u8 *)&i2c_caps,
> +				     TPM_TIS_PHYS_32);
> +	if (ret)
> +		return ret;
> +
> +	phy->guard_time_read = (i2c_caps & TPM_GUARD_TIME_RR_MASK) ||
> +			       (i2c_caps & TPM_GUARD_TIME_RW_MASK);
> +	phy->guard_time_write = (i2c_caps & TPM_GUARD_TIME_WR_MASK) ||
> +				(i2c_caps & TPM_GUARD_TIME_WW_MASK);
> +	phy->guard_time_min = (i2c_caps & TPM_GUARD_TIME_MIN_MASK) >>
> +			      TPM_GUARD_TIME_MIN_SHIFT;
> +	/* guard_time_max = guard_time_min * 1.2 */
> +	phy->guard_time_max = phy->guard_time_min + phy->guard_time_min / 5;
> +
> +	return 0;
> +}
> +
> +static SIMPLE_DEV_PM_OPS(tpm_tis_pm, tpm_pm_suspend, tpm_tis_resume);
> +
> +static const struct tpm_tis_phy_ops tpm_i2c_phy_ops = {
> +	.read_bytes = tpm_tis_i2c_read_bytes,
> +	.write_bytes = tpm_tis_i2c_write_bytes,
> +	.verify_crc = tpm_tis_i2c_verify_crc,
> +};
> +
> +static int tpm_tis_i2c_probe(struct i2c_client *dev,
> +			     const struct i2c_device_id *id)
> +{
> +	struct tpm_tis_i2c_phy *phy;
> +	const u8 crc_enable = 1;
> +	const u8 locality = 0;
> +	int ret;
> +
> +	phy = devm_kzalloc(&dev->dev, sizeof(struct tpm_tis_i2c_phy),
> +			   GFP_KERNEL);
> +	if (!phy)
> +		return -ENOMEM;
> +
> +	phy->io_buf = devm_kzalloc(&dev->dev, TPM_BUFSIZE, GFP_KERNEL);
> +	if (!phy->io_buf)
> +		return -ENOMEM;
> +
> +	phy->i2c_client = dev;
> +
> +	/* must precede all communication with the tpm */
> +	ret = tpm_tis_i2c_init_guard_time(phy);
> +	if (ret)
> +		return ret;
> +
> +	ret = tpm_tis_i2c_write_bytes(&phy->priv, TPM_LOC_SEL, sizeof(locality),
> +				      &locality, TPM_TIS_PHYS_8);
> +	if (ret)
> +		return ret;
> +
> +	ret = tpm_tis_i2c_write_bytes(&phy->priv, TPM_I2C_DATA_CSUM_ENABLE,
> +				      sizeof(crc_enable), &crc_enable,
> +				      TPM_TIS_PHYS_8);
> +	if (ret)
> +		return ret;
> +
> +	return tpm_tis_core_init(&dev->dev, &phy->priv, -1, &tpm_i2c_phy_ops,
> +				 NULL);
> +}
> +
> +static int tpm_tis_i2c_remove(struct i2c_client *client)
> +{
> +	struct tpm_chip *chip = i2c_get_clientdata(client);
> +
> +	tpm_chip_unregister(chip);
> +	tpm_tis_remove(chip);
> +	return 0;
> +}
> +
> +static const struct i2c_device_id tpm_tis_i2c_id[] = {
> +	{ "tpm_tis_i2c", 0 },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, tpm_tis_i2c_id);
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id of_tis_i2c_match[] = {
> +	{ .compatible = "infineon,slb9673", },
> +	{ .compatible = "tcg,tpm-tis-i2c", },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, of_tis_i2c_match);
> +#endif
> +
> +static struct i2c_driver tpm_tis_i2c_driver = {
> +	.driver = {
> +		.owner = THIS_MODULE,
> +		.name = "tpm_tis_i2c",
> +		.pm = &tpm_tis_pm,
> +		.of_match_table = of_match_ptr(of_tis_i2c_match),
> +	},
> +	.probe = tpm_tis_i2c_probe,
> +	.remove = tpm_tis_i2c_remove,
> +	.id_table = tpm_tis_i2c_id,
> +};
> +module_i2c_driver(tpm_tis_i2c_driver);
> +
> +MODULE_DESCRIPTION("TPM Driver for native I2C access");
> +MODULE_LICENSE("GPL");
> -- 
> 2.25.1
> 

Looks quite decent otherwise.

BR, Jarkko