[PATCH v3 2/2] tpm: add driver for cr50 on SPI

[Andrey Pronin <apronin@chromium.org>]

Add TPM2.0 PTP FIFO compatible SPI interface for chips with Cr50
firmware. The firmware running on the currently supported H1
Secure Microcontroller requires a special driver to handle its
specifics:
 - need to ensure a certain delay between spi transactions, or else
   the chip may miss some part of the next transaction;
 - if there is no spi activity for some time, it may go to sleep,
   and needs to be waken up before sending further commands;
 - access to vendor-specific registers.

Signed-off-by: Andrey Pronin <apronin@chromium.org>
---
 drivers/char/tpm/Kconfig    |   9 ++
 drivers/char/tpm/Makefile   |   1 +
 drivers/char/tpm/cr50_spi.c | 350 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 360 insertions(+)
 create mode 100644 drivers/char/tpm/cr50_spi.c

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 9faa0b1..3320acc 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -100,6 +100,15 @@ config TCG_ATMEL
 	  will be accessible from within Linux.  To compile this driver 
 	  as a module, choose M here; the module will be called tpm_atmel.
 
+config TCG_CR50_SPI
+	tristate "TCG PTP FIFO Interface over SPI - Chips with Cr50 Firmware"
+	depends on SPI
+	select TCG_TIS_CORE
+	---help---
+	  If you have a chip running Cr50 firmware on SPI bus, 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 cr50_spi.
+
 config TCG_INFINEON
 	tristate "Infineon Technologies TPM Interface"
 	depends on PNP
diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
index a385fb8..b346306 100644
--- a/drivers/char/tpm/Makefile
+++ b/drivers/char/tpm/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_TCG_TIS_I2C_INFINEON) += tpm_i2c_infineon.o
 obj-$(CONFIG_TCG_TIS_I2C_NUVOTON) += tpm_i2c_nuvoton.o
 obj-$(CONFIG_TCG_NSC) += tpm_nsc.o
 obj-$(CONFIG_TCG_ATMEL) += tpm_atmel.o
+obj-$(CONFIG_TCG_CR50_SPI) += cr50_spi.o
 obj-$(CONFIG_TCG_INFINEON) += tpm_infineon.o
 obj-$(CONFIG_TCG_IBMVTPM) += tpm_ibmvtpm.o
 obj-$(CONFIG_TCG_TIS_ST33ZP24) += st33zp24/
diff --git a/drivers/char/tpm/cr50_spi.c b/drivers/char/tpm/cr50_spi.c
new file mode 100644
index 0000000..57ba8b3
--- /dev/null
+++ b/drivers/char/tpm/cr50_spi.c
@@ -0,0 +1,350 @@
+/*
+ * Copyright (C) 2016 Google, Inc
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2, as published by
+ * the Free Software Foundation.
+ *
+ * This device driver implements a TCG PTP FIFO interface over SPI for chips
+ * with Cr50 firmware.
+ * It is based on tpm_tis_spi driver by Peter Huewe and Christophe Ricard.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/wait.h>
+#include <linux/of.h>
+
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+#include <linux/tpm.h>
+#include "tpm.h"
+#include "tpm_tis_core.h"
+
+/*
+ * Cr50 timing constants:
+ * - can go to sleep not earlier than after CR50_SLEEP_DELAY_MSEC
+ * - needs up to CR50_WAKE_START_DELAY_MSEC to wake after sleep
+ * - requires at least CR50_ACCESS_DELAY_MSEC between transactions
+ */
+#define CR50_SLEEP_DELAY_MSEC			1000
+#define CR50_WAKE_START_DELAY_MSEC		60
+#define CR50_ACCESS_DELAY_MSEC			2
+
+#define MAX_SPI_FRAMESIZE			64
+
+#define TPM_CR50_FW_VER(l)			(0x0F90 | ((l) << 12))
+#define TPM_CR50_MAX_FW_VER_LEN			64
+
+struct cr50_spi_phy {
+	struct tpm_tis_data priv;
+	struct spi_device *spi_device;
+
+	struct mutex time_track_mutex;
+	unsigned long last_access_jiffies;
+	unsigned long wake_after_jiffies;
+
+	unsigned long access_delay_jiffies;
+	unsigned long sleep_delay_jiffies;
+	unsigned int wake_start_delay_msec;
+
+	u8 tx_buf[MAX_SPI_FRAMESIZE];
+	u8 rx_buf[MAX_SPI_FRAMESIZE];
+};
+
+static struct cr50_spi_phy *to_cr50_spi_phy(struct tpm_tis_data *data)
+{
+	return container_of(data, struct cr50_spi_phy, priv);
+}
+
+/*
+ * Cr50 needs to have at least some delay between consecutive
+ * transactions. Make sure we wait.
+ */
+static void cr50_ensure_access_delay(struct cr50_spi_phy *phy)
+{
+	/*
+	 * Note: There is a small chance, if Cr50 is not accessed in a few days,
+	 * that time_in_range will not provide the correct result after the wrap
+	 * around for jiffies. In this case, we'll have an unneeded short delay,
+	 * which is fine.
+	 */
+	unsigned long allowed_access =
+		phy->last_access_jiffies + phy->access_delay_jiffies;
+	unsigned long time_now = jiffies;
+
+	if (time_in_range_open(time_now,
+			       phy->last_access_jiffies, allowed_access))
+		mdelay(jiffies_to_msecs(allowed_access - time_now));
+}
+
+/*
+ * Cr50 might go to sleep if there is no SPI activity for some time and
+ * miss the first few bits/bytes on the bus. In such case, wake it up
+ * by asserting CS and give it time to start up.
+ */
+static bool cr50_needs_waking(struct cr50_spi_phy *phy)
+{
+	/*
+	 * Note: There is a small chance, if Cr50 is not accessed in a few days,
+	 * that time_in_range will not provide the correct result after the wrap
+	 * around for jiffies. In this case, we'll probably timeout or read
+	 * incorrect value from TPM_STS and just retry the operation.
+	 */
+	return !time_in_range_open(jiffies,
+				   phy->last_access_jiffies,
+				   phy->wake_after_jiffies);
+}
+
+static void cr50_wake_if_needed(struct cr50_spi_phy *phy)
+{
+	if (cr50_needs_waking(phy)) {
+		/* Assert CS, wait 1 msec, deassert CS */
+		struct spi_transfer spi_cs_wake = { .delay_usecs = 1000 };
+
+		spi_sync_transfer(phy->spi_device, &spi_cs_wake, 1);
+		/* Wait for it to fully wake */
+		msleep(phy->wake_start_delay_msec);
+	}
+	/* Reset the time when we need to wake Cr50 again */
+	phy->wake_after_jiffies = jiffies + phy->sleep_delay_jiffies;
+}
+
+/*
+ * Flow control: clock the bus and wait for cr50 to set LSB before
+ * sending/receiving data. TCG PTP spec allows it to happen during
+ * the last byte of header, but cr50 never does that in practice,
+ * and earlier versions had a bug when it was set too early, so don't
+ * check for it during header transfer.
+ */
+static int cr50_spi_flow_control(struct cr50_spi_phy *phy)
+{
+	unsigned long timeout_jiffies =
+		jiffies + msecs_to_jiffies(TPM_RETRY * TPM_TIMEOUT_RETRY);
+	struct spi_message m;
+	int ret;
+	struct spi_transfer spi_xfer = {
+		.rx_buf = phy->rx_buf,
+		.len = 1,
+		.cs_change = 1,
+	};
+
+	do {
+		spi_message_init(&m);
+		spi_message_add_tail(&spi_xfer, &m);
+		ret = spi_sync_locked(phy->spi_device, &m);
+		if (ret < 0)
+			return ret;
+		if (time_after(jiffies, timeout_jiffies))
+			return -EBUSY;
+	} while (!(phy->rx_buf[0] & 0x01));
+	return 0;
+}
+
+static int cr50_spi_xfer_bytes(struct tpm_tis_data *data, u32 addr,
+			       u16 len, u8 *buf, bool do_write)
+{
+	struct cr50_spi_phy *phy = to_cr50_spi_phy(data);
+	struct spi_message m;
+	struct spi_transfer spi_xfer = {
+		.tx_buf = phy->tx_buf,
+		.rx_buf = phy->rx_buf,
+		.len = 4,
+		.cs_change = 1,
+	};
+	int ret;
+
+	if (len > MAX_SPI_FRAMESIZE)
+		return -EINVAL;
+
+	/*
+	 * Do this outside of spi_bus_lock in case cr50 is not the
+	 * only device on that spi bus.
+	 */
+	mutex_lock(&phy->time_track_mutex);
+	cr50_ensure_access_delay(phy);
+	cr50_wake_if_needed(phy);
+
+	phy->tx_buf[0] = (do_write ? 0x00 : 0x80) | (len - 1);
+	phy->tx_buf[1] = 0xD4;
+	phy->tx_buf[2] = (addr >> 8) & 0xFF;
+	phy->tx_buf[3] = addr & 0xFF;
+
+	spi_message_init(&m);
+	spi_message_add_tail(&spi_xfer, &m);
+
+	spi_bus_lock(phy->spi_device->master);
+	ret = spi_sync_locked(phy->spi_device, &m);
+	if (ret < 0)
+		goto exit;
+
+	ret = cr50_spi_flow_control(phy);
+	if (ret < 0)
+		goto exit;
+
+	spi_xfer.cs_change = 0;
+	spi_xfer.len = len;
+	if (do_write) {
+		memcpy(phy->tx_buf, buf, len);
+		spi_xfer.rx_buf = NULL;
+	} else {
+		spi_xfer.tx_buf = NULL;
+	}
+
+	spi_message_init(&m);
+	spi_message_add_tail(&spi_xfer, &m);
+	ret = spi_sync_locked(phy->spi_device, &m);
+	if (!do_write)
+		memcpy(buf, phy->rx_buf, len);
+
+exit:
+	spi_bus_unlock(phy->spi_device->master);
+	phy->last_access_jiffies = jiffies;
+	mutex_unlock(&phy->time_track_mutex);
+
+	return ret;
+}
+
+static int cr50_spi_read_bytes(struct tpm_tis_data *data, u32 addr,
+			       u16 len, u8 *result)
+{
+	return cr50_spi_xfer_bytes(data, addr, len, result, false);
+}
+
+static int cr50_spi_write_bytes(struct tpm_tis_data *data, u32 addr,
+				u16 len, u8 *value)
+{
+	return cr50_spi_xfer_bytes(data, addr, len, value, true);
+}
+
+static int cr50_spi_read16(struct tpm_tis_data *data, u32 addr, u16 *result)
+{
+	int rc;
+	__le16 le_val;
+
+	rc = data->phy_ops->read_bytes(data, addr, sizeof(u16), (u8 *)&le_val);
+	if (!rc)
+		*result = le16_to_cpu(le_val);
+	return rc;
+}
+
+static int cr50_spi_read32(struct tpm_tis_data *data, u32 addr, u32 *result)
+{
+	int rc;
+	__le32 le_val;
+
+	rc = data->phy_ops->read_bytes(data, addr, sizeof(u32), (u8 *)&le_val);
+	if (!rc)
+		*result = le32_to_cpu(le_val);
+	return rc;
+}
+
+static int cr50_spi_write32(struct tpm_tis_data *data, u32 addr, u32 value)
+{
+	__le32 le_val = cpu_to_le32(value);
+
+	return data->phy_ops->write_bytes(data, addr, sizeof(u32),
+					   (u8 *)&le_val);
+}
+
+static void cr50_get_fw_version(struct tpm_tis_data *data, char *fw_ver)
+{
+	int i, len = 0;
+	char fw_ver_block[4];
+
+	/*
+	 * Write anything to TPM_CR50_FW_VER to start from the beginning
+	 * of the version string
+	 */
+	tpm_tis_write8(data, TPM_CR50_FW_VER(data->locality), 0);
+
+	/* Read the string, 4 bytes at a time, until we get '\0' */
+	do {
+		tpm_tis_read_bytes(data, TPM_CR50_FW_VER(data->locality), 4,
+				   fw_ver_block);
+		for (i = 0; i < 4 && fw_ver_block[i]; ++len, ++i)
+			fw_ver[len] = fw_ver_block[i];
+	} while (i == 4 && len < TPM_CR50_MAX_FW_VER_LEN);
+	fw_ver[len] = 0;
+}
+
+static const struct tpm_tis_phy_ops cr50_spi_phy_ops = {
+	.read_bytes = cr50_spi_read_bytes,
+	.write_bytes = cr50_spi_write_bytes,
+	.read16 = cr50_spi_read16,
+	.read32 = cr50_spi_read32,
+	.write32 = cr50_spi_write32,
+	.max_xfer_size = MAX_SPI_FRAMESIZE,
+};
+
+static int cr50_spi_probe(struct spi_device *dev)
+{
+	char fw_ver[TPM_CR50_MAX_FW_VER_LEN + 1];
+	struct cr50_spi_phy *phy;
+	int rc;
+
+	phy = devm_kzalloc(&dev->dev, sizeof(struct cr50_spi_phy),
+			   GFP_KERNEL);
+	if (!phy)
+		return -ENOMEM;
+
+	phy->spi_device = dev;
+
+	phy->access_delay_jiffies = CR50_ACCESS_DELAY_MSEC;
+	phy->sleep_delay_jiffies = CR50_SLEEP_DELAY_MSEC;
+	phy->wake_start_delay_msec = CR50_WAKE_START_DELAY_MSEC;
+
+	mutex_init(&phy->time_track_mutex);
+	phy->wake_after_jiffies = jiffies;
+	phy->last_access_jiffies = jiffies;
+
+	rc = tpm_tis_core_init(&dev->dev, &phy->priv, -1, &cr50_spi_phy_ops,
+			       NULL);
+	if (rc < 0)
+		return rc;
+
+	cr50_get_fw_version(&phy->priv, fw_ver);
+	dev_info(&dev->dev, "Cr50 firmware version: %s\n", fw_ver);
+
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(cr50_pm, tpm_pm_suspend, tpm_tis_resume);
+
+static int cr50_spi_remove(struct spi_device *dev)
+{
+	struct tpm_chip *chip = spi_get_drvdata(dev);
+
+	tpm_chip_unregister(chip);
+	tpm_tis_remove(chip);
+	return 0;
+}
+
+static const struct spi_device_id cr50_spi_id[] = {
+	{ "cr50", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, cr50_spi_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id of_cr50_spi_match[] = {
+	{ .compatible = "google,cr50", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, of_cr50_spi_match);
+#endif
+
+static struct spi_driver cr50_spi_driver = {
+	.driver = {
+		.name = "cr50_spi",
+		.pm = &cr50_pm,
+		.of_match_table = of_match_ptr(of_cr50_spi_match),
+	},
+	.probe = cr50_spi_probe,
+	.remove = cr50_spi_remove,
+	.id_table = cr50_spi_id,
+};
+module_spi_driver(cr50_spi_driver);
+
+MODULE_DESCRIPTION("Cr50 TCG PTP FIFO SPI driver");
+MODULE_LICENSE("GPL v2");
-- 
2.6.6