[PATCH v2 5/6] misc: amd-sbi: Add SBTSI ioctl register transfer interface
From: Akshay Gupta
Date: Fri May 15 2026 - 09:51:16 EST
From: Prathima <Prathima.Lk@xxxxxxx>
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@xxxxxxx>
Signed-off-by: Prathima <Prathima.Lk@xxxxxxx>
---
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