[PATCH v2 5/6] misc: amd-sbi: Add SBTSI ioctl register transfer interface

[Akshay Gupta <Akshay.Gupta@amd.com>]

From: Prathima <Prathima.Lk@amd.com>

Implement IOCTL interface for SB-TSI driver to enable userspace access
to TSI register read/write operations through the AMD Advanced Platform
Management Link (APML) protocol.
Add an ioctl command (SBTSI_IOCTL_REG_XFER_CMD) that accepts a register
address, data byte, and direction flag. Serialize access with a mutex
shared between the hwmon and ioctl paths to prevent concurrent bus
transactions from corrupting register state.

Reviewed-by: Akshay Gupta <Akshay.Gupta@amd.com>
Signed-off-by: Prathima <Prathima.Lk@amd.com>
---
Changes since v1:
- Use of devm_mutex_init in place of mutex_init
- Use of guard_mutex in place of mutex_lock()/mutex_unlock()
- Use of devm_add_action_or_reset() for clean removal
 
 drivers/hwmon/sbtsi_temp.c      |  6 +++
 drivers/misc/amd-sbi/tsi-core.c | 84 ++++++++++++++++++++++++++++++++-
 drivers/misc/amd-sbi/tsi-core.h | 15 ++++++
 drivers/misc/amd-sbi/tsi.c      | 20 ++++++--
 include/linux/misc/tsi.h        |  8 ++++
 include/uapi/misc/amd-apml.h    | 23 +++++++++
 6 files changed, 151 insertions(+), 5 deletions(-)
 create mode 100644 drivers/misc/amd-sbi/tsi-core.h

diff --git a/drivers/hwmon/sbtsi_temp.c b/drivers/hwmon/sbtsi_temp.c
index d7ae986d824c..00e982f4c716 100644
--- a/drivers/hwmon/sbtsi_temp.c
+++ b/drivers/hwmon/sbtsi_temp.c
@@ -64,12 +64,15 @@ static inline void sbtsi_mc_to_reg(s32 temp, u8 *integer, u8 *decimal)
 /*
  * Read integer and decimal parts of an SB-TSI temperature register pair
  * The read order is determined by the ReadOrder bit to ensure atomic latching.
+ * The mutex protects against concurrent access to the shared I2C/I3C bus by
+ * the hwmon sysfs and a userspace ioctl
  */
 static int sbtsi_temp_read(struct sbtsi_data *data, u8 reg1, u8 reg2,
 			   u8 *val1, u8 *val2)
 {
 	int ret;
 
+	guard(mutex)(&data->lock);
 	ret = sbtsi_xfer(data, reg1, val1, true);
 	if (!ret)
 		ret = sbtsi_xfer(data, reg2, val2, true);
@@ -78,12 +81,15 @@ static int sbtsi_temp_read(struct sbtsi_data *data, u8 reg1, u8 reg2,
 
 /*
  * Write integer and decimal parts of an SB-TSI temperature register pair.
+ * The mutex protects against concurrent access to the shared I2C/I3C bus by
+ * the hwmon sysfs and a userspace ioctl
  */
 static int sbtsi_temp_write(struct sbtsi_data *data, u8 reg_int, u8 reg_dec,
 			    u8 val_int, u8 val_dec)
 {
 	int ret;
 
+	guard(mutex)(&data->lock);
 	ret = sbtsi_xfer(data, reg_int, &val_int, false);
 	if (!ret)
 		ret = sbtsi_xfer(data, reg_dec, &val_dec, false);
diff --git a/drivers/misc/amd-sbi/tsi-core.c b/drivers/misc/amd-sbi/tsi-core.c
index 19388737b225..c5bd60409d5b 100644
--- a/drivers/misc/amd-sbi/tsi-core.c
+++ b/drivers/misc/amd-sbi/tsi-core.c
@@ -6,8 +6,12 @@
  * Copyright (C) 2026 Advanced Micro Devices, Inc.
  */
 
+#include <linux/fs.h>
+#include <linux/ioctl.h>
 #include <linux/module.h>
-#include <linux/misc/tsi.h>
+#include <linux/uaccess.h>
+#include <uapi/misc/amd-apml.h>
+#include "tsi-core.h"
 
 /* I2C transfer function */
 static int sbtsi_i2c_xfer(struct sbtsi_data *data, u8 reg, u8 *val, bool is_read)
@@ -62,7 +66,83 @@ int sbtsi_xfer(struct sbtsi_data *data, u8 reg, u8 *val, bool is_read)
 	if (data->is_i3c)
 		return is_read ? sbtsi_i3c_read(data, reg, val)
 			       : sbtsi_i3c_write(data, reg, *val);
-
 	return sbtsi_i2c_xfer(data, reg, val, is_read);
 }
 EXPORT_SYMBOL_GPL(sbtsi_xfer);
+
+/*
+ * The mutex protects against concurrent access to the shared I2C/I3C bus by
+ * the hwmon sysfs and a userspace ioctl.
+ */
+static int sbtsi_xfer_ioctl(struct sbtsi_data *data, u8 reg, u8 *val, bool is_read)
+{
+	guard(mutex)(&data->lock);
+	return sbtsi_xfer(data, reg, val, is_read);
+}
+
+static int apml_tsi_reg_xfer(struct sbtsi_data *data,
+			     struct apml_tsi_xfer_msg __user *arg)
+{
+	struct apml_tsi_xfer_msg msg = { 0 };
+	int ret;
+
+	if (copy_from_user(&msg, arg, sizeof(struct apml_tsi_xfer_msg)))
+		return -EFAULT;
+
+	ret = sbtsi_xfer_ioctl(data, msg.reg_addr, &msg.data_in_out, msg.rflag);
+
+	if (msg.rflag && !ret) {
+		if (copy_to_user(arg, &msg, sizeof(struct apml_tsi_xfer_msg)))
+			return -EFAULT;
+	}
+	return ret;
+}
+
+static long sbtsi_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+	struct sbtsi_data *data;
+
+	data = container_of(fp->private_data, struct sbtsi_data, sbtsi_misc_dev);
+	switch (cmd) {
+	case SBTSI_IOCTL_REG_XFER_CMD:
+		return apml_tsi_reg_xfer(data, argp);
+	default:
+		return -ENOTTY;
+	}
+}
+
+static const struct file_operations sbtsi_fops = {
+	.owner		= THIS_MODULE,
+	.unlocked_ioctl	= sbtsi_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+};
+
+static void sbtsi_misc_deregister(void *data)
+{
+	misc_deregister((struct miscdevice *)data);
+}
+
+int create_misc_tsi_device(struct sbtsi_data *data, struct device *dev)
+{
+	int ret;
+
+	data->sbtsi_misc_dev.name = devm_kasprintf(dev, GFP_KERNEL,
+						   "sbtsi-%x", data->dev_addr);
+	if (!data->sbtsi_misc_dev.name)
+		return -ENOMEM;
+	data->sbtsi_misc_dev.minor    = MISC_DYNAMIC_MINOR;
+	data->sbtsi_misc_dev.fops     = &sbtsi_fops;
+	data->sbtsi_misc_dev.parent   = dev;
+	data->sbtsi_misc_dev.nodename = devm_kasprintf(dev, GFP_KERNEL,
+						       "sbtsi-%x", data->dev_addr);
+	if (!data->sbtsi_misc_dev.nodename)
+		return -ENOMEM;
+	data->sbtsi_misc_dev.mode = 0600;
+
+	ret = misc_register(&data->sbtsi_misc_dev);
+	if (ret)
+		return ret;
+	return devm_add_action_or_reset(dev, sbtsi_misc_deregister,
+					&data->sbtsi_misc_dev);
+}
diff --git a/drivers/misc/amd-sbi/tsi-core.h b/drivers/misc/amd-sbi/tsi-core.h
new file mode 100644
index 000000000000..7bf967a09837
--- /dev/null
+++ b/drivers/misc/amd-sbi/tsi-core.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * AMD SBTSI misc tsi device .
+ *
+ * Copyright (C) 2026 Advanced Micro Devices, Inc.
+ */
+
+#ifndef _LINUX_TSI_CORE_H_
+#define _LINUX_TSI_CORE_H_
+
+#include <linux/misc/tsi.h>
+
+int create_misc_tsi_device(struct sbtsi_data *data, struct device *dev);
+
+#endif /* _LINUX_TSI_CORE_H_ */
diff --git a/drivers/misc/amd-sbi/tsi.c b/drivers/misc/amd-sbi/tsi.c
index 43bbac7faf08..6a9356740f4e 100644
--- a/drivers/misc/amd-sbi/tsi.c
+++ b/drivers/misc/amd-sbi/tsi.c
@@ -10,8 +10,8 @@
 #include <linux/bitfield.h>
 #include <linux/module.h>
 #include <linux/of.h>
-#include <linux/misc/tsi.h>
 #include <linux/slab.h>
+#include "tsi-core.h"
 
 #define SBTSI_REG_CONFIG		0x03 /* RO */
 
@@ -89,6 +89,9 @@ static int sbtsi_i2c_probe(struct i2c_client *client)
 	if (!data)
 		return -ENOMEM;
 
+	err = devm_mutex_init(dev, &data->lock);
+	if (err)
+		return err;
 	data->is_i3c = false;
 	data->client = client;
 	err = i2c_smbus_read_byte_data(data->client, SBTSI_REG_CONFIG);
@@ -98,7 +101,11 @@ static int sbtsi_i2c_probe(struct i2c_client *client)
 	data->read_order = FIELD_GET(BIT(SBTSI_CONFIG_READ_ORDER_SHIFT), err);
 
 	dev_set_drvdata(dev, data);
-	return sbtsi_create_hwmon_adev(dev, client->addr);
+	err = sbtsi_create_hwmon_adev(dev, client->addr);
+	if (err < 0)
+		return err;
+	data->dev_addr = client->addr;
+	return create_misc_tsi_device(data, dev);
 }
 
 static const struct i2c_device_id sbtsi_id[] = {
@@ -145,6 +152,9 @@ static int sbtsi_i3c_probe(struct i3c_device *i3cdev)
 	if (!data)
 		return -ENOMEM;
 
+	err = devm_mutex_init(dev, &data->lock);
+	if (err)
+		return err;
 	data->i3cdev = i3cdev;
 	data->is_i3c = true;
 
@@ -156,7 +166,11 @@ static int sbtsi_i3c_probe(struct i3c_device *i3cdev)
 	data->read_order = FIELD_GET(BIT(SBTSI_CONFIG_READ_ORDER_SHIFT), val);
 
 	dev_set_drvdata(dev, data);
-	return sbtsi_create_hwmon_adev(dev, i3cdev->desc->info.dyn_addr);
+	err = sbtsi_create_hwmon_adev(dev, i3cdev->desc->info.dyn_addr);
+	if (err < 0)
+		return err;
+	data->dev_addr = i3cdev->desc->info.dyn_addr;
+	return create_misc_tsi_device(data, dev);
 }
 
 static const struct i3c_device_id sbtsi_i3c_id[] = {
diff --git a/include/linux/misc/tsi.h b/include/linux/misc/tsi.h
index 7ce689081427..184b1aa14f0a 100644
--- a/include/linux/misc/tsi.h
+++ b/include/linux/misc/tsi.h
@@ -11,12 +11,17 @@
 #include <linux/i2c.h>
 #include <linux/i3c/device.h>
 #include <linux/i3c/master.h>
+#include <linux/miscdevice.h>
+#include <linux/mutex.h>
 #include <linux/types.h>
 
 /**
  * struct sbtsi_data - driver private data for an AMD SB-TSI device
  * @client:	underlying I2C client
  * @i3cdev:	underlying I3C device (when using I3C bus)
+ * @sbtsi_misc_dev: miscdevice exposing ioctl interface at /dev/sbtsi-<addr>
+ * @lock:           mutex protecting concurrent access to the device
+ * @dev_addr:       I2C/I3C device address, used to name the misc device node
  * @ext_range_mode:	sensor uses extended temperature range
  * @read_order:	if set, decimal part must be read before integer part
  * @is_i3c:	true when the device is accessed over I3C
@@ -26,6 +31,9 @@ struct sbtsi_data {
 		struct i2c_client *client;
 		struct i3c_device *i3cdev;
 	};
+	struct miscdevice sbtsi_misc_dev;
+	struct mutex lock;	/* protects concurrent access to the device */
+	u8 dev_addr;
 	bool ext_range_mode;
 	bool read_order;
 	bool is_i3c;
diff --git a/include/uapi/misc/amd-apml.h b/include/uapi/misc/amd-apml.h
index 745b3338fc06..8a85f79b0938 100644
--- a/include/uapi/misc/amd-apml.h
+++ b/include/uapi/misc/amd-apml.h
@@ -73,6 +73,13 @@ struct apml_reg_xfer_msg {
 	__u8 rflag;
 };
 
+struct apml_tsi_xfer_msg {
+	__u8 reg_addr;		/* TSI register address offset */
+	__u8 data_in_out;	/* Register data for read/write */
+	__u8 rflag;		/* Register read or write */
+	__u8 pad;		/* Explicit padding */
+};
+
 /*
  * AMD sideband interface base IOCTL
  */
@@ -149,4 +156,20 @@ struct apml_reg_xfer_msg {
  */
 #define SBRMI_IOCTL_REG_XFER_CMD	_IOWR(SB_BASE_IOCTL_NR, 3, struct apml_reg_xfer_msg)
 
+/**
+ * DOC: SBTSI_IOCTL_REG_XFER_CMD
+ *
+ * @Parameters
+ *
+ * @struct apml_tsi_xfer_msg
+ *	Pointer to the &struct apml_tsi_xfer_msg that will contain the protocol
+ *	information
+ *
+ * @Description
+ * IOCTL command for APML TSI messages using generic _IOWR
+ * The IOCTL provides userspace access to AMD sideband TSI register xfer protocol
+ * - TSI protocol to read/write temperature sensor registers
+ */
+#define SBTSI_IOCTL_REG_XFER_CMD	_IOWR(SB_BASE_IOCTL_NR, 4, struct apml_tsi_xfer_msg)
+
 #endif /*_AMD_APML_H_*/
-- 
2.34.1