tpm: Add tpm_tis_i2c backend for tpm_tis_core

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>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

1 files changed, 391 insertions, 0 deletions

diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
new file mode 100644
index 000000000000..8e0686fe4eb1
--- /dev/null
+++ b/drivers/char/tpm/tpm_tis_i2c.c
@@ -0,0 +1,391 @@
+// 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", },
+	{}
+};
+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");