kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

6 files changed, 1061 insertions, 0 deletions

diff --git a/drivers/misc/amd-sbi/Kconfig b/drivers/misc/amd-sbi/Kconfig
new file mode 100644
index 000000000..30e7fad73
--- /dev/null
+++ b/drivers/misc/amd-sbi/Kconfig
@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config AMD_SBRMI_I2C
+	tristate "AMD side band RMI support"
+	depends on I3C_OR_I2C
+	depends on ARM || ARM64 || COMPILE_TEST
+	select REGMAP_I2C
+	select REGMAP_I3C if I3C
+	help
+	  Side band RMI over I2C/I3C support for AMD out of band management.
+	  This driver is intended to run on the BMC, not the managed node.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called sbrmi-i2c.
+
+config AMD_SBRMI_HWMON
+	bool "SBRMI hardware monitoring"
+	depends on AMD_SBRMI_I2C && HWMON
+	depends on !(AMD_SBRMI_I2C=y && HWMON=m)
+	help
+	  This provides support for RMI device hardware monitoring. If enabled,
+	  a hardware monitoring device will be created for each socket in
+	  the system.
diff --git a/drivers/misc/amd-sbi/Makefile b/drivers/misc/amd-sbi/Makefile
new file mode 100644
index 000000000..38eaaa651
--- /dev/null
+++ b/drivers/misc/amd-sbi/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
+sbrmi-i2c-objs  		+= rmi-i2c.o rmi-core.o
+sbrmi-i2c-$(CONFIG_AMD_SBRMI_HWMON)	+= rmi-hwmon.o
+obj-$(CONFIG_AMD_SBRMI_I2C)	+= sbrmi-i2c.o
diff --git a/drivers/misc/amd-sbi/rmi-core.c b/drivers/misc/amd-sbi/rmi-core.c
new file mode 100644
index 000000000..d4238ebad
--- /dev/null
+++ b/drivers/misc/amd-sbi/rmi-core.c
@@ -0,0 +1,594 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * sbrmi-core.c - file defining SB-RMI protocols compliant
+ *		  AMD SoC device.
+ *
+ * Copyright (C) 2025 Advanced Micro Devices, Inc.
+ */
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/fs.h>
+#include <linux/i2c.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/regmap.h>
+#include "rmi-core.h"
+
+/* Mask for Status Register bit[1] */
+#define SW_ALERT_MASK	0x2
+/* Mask to check H/W Alert status bit */
+#define HW_ALERT_MASK	0x80
+
+/* Software Interrupt for triggering */
+#define START_CMD	0x80
+#define TRIGGER_MAILBOX	0x01
+
+/* Default message lengths as per APML command protocol */
+/* CPUID */
+#define CPUID_RD_DATA_LEN	0x8
+#define CPUID_WR_DATA_LEN	0x8
+#define CPUID_WR_DATA_LEN_EXT	0x9
+#define CPUID_RD_REG_LEN	0xa
+#define CPUID_WR_REG_LEN	0x9
+#define CPUID_WR_REG_LEN_EXT	0xa
+/* MSR */
+#define MSR_RD_REG_LEN		0xa
+#define MSR_WR_REG_LEN		0x8
+#define MSR_WR_REG_LEN_EXT	0x9
+#define MSR_RD_DATA_LEN		0x8
+#define MSR_WR_DATA_LEN		0x7
+#define MSR_WR_DATA_LEN_EXT	0x8
+
+/* CPUID MSR Command Ids */
+#define CPUID_MCA_CMD	0x73
+#define RD_CPUID_CMD	0x91
+#define RD_MCA_CMD	0x86
+
+/* CPUID MCAMSR mask & index */
+#define CPUID_MCA_THRD_INDEX	32
+#define CPUID_MCA_FUNC_MASK	GENMASK(31, 0)
+#define CPUID_EXT_FUNC_INDEX	48
+
+/* input for bulk write to CPUID protocol */
+struct cpu_msr_indata {
+	u8 wr_len;	/* const value */
+	u8 rd_len;	/* const value */
+	u8 proto_cmd;	/* const value */
+	u8 thread;	/* thread number */
+	union {
+		u8 reg_offset[4];	/* input value */
+		u32 value;
+	} __packed;
+	u8 ext; /* extended function */
+};
+
+/* input for bulk write to CPUID protocol for REV 0x21 */
+struct cpu_msr_indata_ext {
+	u8 wr_len;	/* const value */
+	u8 rd_len;	/* const value */
+	u8 proto_cmd;	/* const value */
+	u8 thread_lo;	/* thread number low */
+	u8 thread_hi;	/* thread number high */
+	union {
+		u8 reg_offset[4];	/* input value */
+		u32 value;
+	} __packed;
+	u8 ext; /* extended function */
+};
+
+/* output for bulk read from CPUID protocol */
+struct cpu_msr_outdata {
+	u8 num_bytes;	/* number of bytes return */
+	u8 status;	/* Protocol status code */
+	union {
+		u64 value;
+		u8 reg_data[8];
+	} __packed;
+};
+
+static inline void prepare_cpuid_input_message(struct cpu_msr_indata *input,
+					       u8 thread_id, u32 func,
+					       u8 ext_func)
+{
+	input->rd_len		= CPUID_RD_DATA_LEN;
+	input->wr_len		= CPUID_WR_DATA_LEN;
+	input->proto_cmd	= RD_CPUID_CMD;
+	input->thread		= thread_id << 1;
+	input->value		= func;
+	input->ext		= ext_func;
+}
+
+static inline void prepare_cpuid_input_message_ext(struct cpu_msr_indata_ext *input,
+						   u16 thread_id, u32 func,
+						   u8 ext_func)
+{
+	input->rd_len		= CPUID_RD_DATA_LEN;
+	input->wr_len		= CPUID_WR_DATA_LEN_EXT;
+	input->proto_cmd	= RD_CPUID_CMD;
+	input->thread_lo	= (thread_id & 0xFF) << 1;
+	input->thread_hi	= thread_id >> 8;
+	input->value		= func;
+	input->ext		= ext_func;
+}
+
+static inline void prepare_mca_msr_input_message(struct cpu_msr_indata *input,
+						 u8 thread_id, u32 data_in)
+{
+	input->rd_len		= MSR_RD_DATA_LEN;
+	input->wr_len		= MSR_WR_DATA_LEN;
+	input->proto_cmd	= RD_MCA_CMD;
+	input->thread		= thread_id << 1;
+	input->value		= data_in;
+}
+
+static inline void prepare_mca_msr_input_message_ext(struct cpu_msr_indata_ext *input,
+						     u16 thread_id, u32 data_in)
+{
+	input->rd_len		= MSR_RD_DATA_LEN;
+	input->wr_len		= MSR_WR_DATA_LEN_EXT;
+	input->proto_cmd	= RD_MCA_CMD;
+	input->thread_lo	= (thread_id & 0xFF) << 1;
+	input->thread_hi	= thread_id >> 8;
+	input->value		= data_in;
+}
+
+static int sbrmi_get_rev(struct sbrmi_data *data)
+{
+	unsigned int rev;
+	u16 offset = SBRMI_REV;
+	int ret;
+
+	ret = regmap_read(data->regmap, offset, &rev);
+	if (ret < 0)
+		return ret;
+
+	data->rev = rev;
+	return 0;
+}
+
+static int rmi_cpuid_input(struct sbrmi_data *data, struct apml_cpuid_msg *msg,
+			   u16 thread)
+{
+	struct cpu_msr_indata input = {0};
+	int val = 0, ret;
+
+	/* Thread > 127, Thread128 CS register, 1'b1 needs to be set to 1 */
+	if (thread > 127) {
+		thread -= 128;
+		val = 1;
+	}
+
+	ret = regmap_write(data->regmap, SBRMI_THREAD128CS, val);
+	if (ret < 0)
+		return ret;
+
+	prepare_cpuid_input_message(&input, thread,
+				    msg->cpu_in_out & CPUID_MCA_FUNC_MASK,
+				    msg->cpu_in_out >> CPUID_EXT_FUNC_INDEX);
+
+	return regmap_bulk_write(data->regmap, CPUID_MCA_CMD,
+				 &input, CPUID_WR_REG_LEN);
+}
+
+static int rmi_cpuid_input_ext(struct sbrmi_data *data, struct apml_cpuid_msg *msg,
+			       u16 thread)
+{
+	struct cpu_msr_indata_ext input = {0};
+
+	prepare_cpuid_input_message_ext(&input, thread,
+					msg->cpu_in_out & CPUID_MCA_FUNC_MASK,
+					msg->cpu_in_out >> CPUID_EXT_FUNC_INDEX);
+
+	return regmap_bulk_write(data->regmap, CPUID_MCA_CMD,
+				 &input, CPUID_WR_REG_LEN_EXT);
+}
+
+/* Read CPUID function protocol */
+static int rmi_cpuid_read(struct sbrmi_data *data,
+			  struct apml_cpuid_msg *msg)
+{
+	struct cpu_msr_outdata output = {0};
+	int ret, hw_status;
+	u16 thread;
+
+	mutex_lock(&data->lock);
+	/* cache the rev value to identify if protocol is supported or not */
+	if (!data->rev) {
+		ret = sbrmi_get_rev(data);
+		if (ret < 0)
+			goto exit_unlock;
+	}
+
+	/* Extract thread from the input msg structure */
+	thread = msg->cpu_in_out >> CPUID_MCA_THRD_INDEX;
+
+	switch (data->rev) {
+	case 0x10:
+		/* CPUID protocol for REV 0x10 is not supported*/
+		ret = -EOPNOTSUPP;
+		goto exit_unlock;
+	case 0x20:
+		ret = rmi_cpuid_input(data, msg, thread);
+		if (ret)
+			goto exit_unlock;
+		break;
+	case 0x21:
+	case 0x31:
+		ret = rmi_cpuid_input_ext(data, msg, thread);
+		if (ret)
+			goto exit_unlock;
+		break;
+	default:
+		ret = -EOPNOTSUPP;
+		goto exit_unlock;
+	}
+
+	/*
+	 * For RMI Rev 0x20, new h/w status bit is introduced. which is used
+	 * by firmware to indicate completion of commands (0x71, 0x72, 0x73).
+	 * wait for the status bit to be set by the hardware before
+	 * reading the data out.
+	 */
+	ret = regmap_read_poll_timeout(data->regmap, SBRMI_STATUS, hw_status,
+				       hw_status & HW_ALERT_MASK, 500, 2000000);
+	if (ret)
+		goto exit_unlock;
+
+	ret = regmap_bulk_read(data->regmap, CPUID_MCA_CMD,
+			       &output, CPUID_RD_REG_LEN);
+	if (ret < 0)
+		goto exit_unlock;
+
+	ret = regmap_write(data->regmap, SBRMI_STATUS,
+			   HW_ALERT_MASK);
+	if (ret < 0)
+		goto exit_unlock;
+
+	if (output.num_bytes != CPUID_RD_REG_LEN - 1) {
+		ret = -EMSGSIZE;
+		goto exit_unlock;
+	}
+	if (output.status) {
+		ret = -EPROTOTYPE;
+		msg->fw_ret_code = output.status;
+		goto exit_unlock;
+	}
+	msg->cpu_in_out = output.value;
+exit_unlock:
+	if (ret < 0)
+		msg->cpu_in_out = 0;
+	mutex_unlock(&data->lock);
+	return ret;
+}
+
+static int rmi_mcamsr_input(struct sbrmi_data *data, struct apml_mcamsr_msg *msg,
+			    u16 thread)
+{
+	struct cpu_msr_indata input = {0};
+	int val = 0, ret;
+
+	/* Thread > 127, Thread128 CS register, 1'b1 needs to be set to 1 */
+	if (thread > 127) {
+		thread -= 128;
+		val = 1;
+	}
+
+	ret = regmap_write(data->regmap, SBRMI_THREAD128CS, val);
+	if (ret < 0)
+		return ret;
+
+	prepare_mca_msr_input_message(&input, thread,
+				      msg->mcamsr_in_out & CPUID_MCA_FUNC_MASK);
+
+	return regmap_bulk_write(data->regmap, CPUID_MCA_CMD,
+				 &input, MSR_WR_REG_LEN);
+}
+
+static int rmi_mcamsr_input_ext(struct sbrmi_data *data, struct apml_mcamsr_msg *msg,
+				u16 thread)
+{
+	struct cpu_msr_indata_ext input = {0};
+
+	prepare_mca_msr_input_message_ext(&input, thread,
+					  msg->mcamsr_in_out & CPUID_MCA_FUNC_MASK);
+
+	return regmap_bulk_write(data->regmap, CPUID_MCA_CMD,
+				 &input, MSR_WR_REG_LEN_EXT);
+}
+
+/* MCA MSR protocol */
+static int rmi_mca_msr_read(struct sbrmi_data *data,
+			    struct apml_mcamsr_msg  *msg)
+{
+	struct cpu_msr_outdata output = {0};
+	int ret;
+	int hw_status;
+	u16 thread;
+
+	mutex_lock(&data->lock);
+	/* cache the rev value to identify if protocol is supported or not */
+	if (!data->rev) {
+		ret = sbrmi_get_rev(data);
+		if (ret < 0)
+			goto exit_unlock;
+	}
+
+	/* Extract thread from the input msg structure */
+	thread = msg->mcamsr_in_out >> CPUID_MCA_THRD_INDEX;
+
+	switch (data->rev) {
+	case 0x10:
+		/* MCAMSR protocol for REV 0x10 is not supported*/
+		ret = -EOPNOTSUPP;
+		goto exit_unlock;
+	case 0x20:
+		ret = rmi_mcamsr_input(data, msg, thread);
+		if (ret)
+			goto exit_unlock;
+		break;
+	case 0x21:
+	case 0x31:
+		ret = rmi_mcamsr_input_ext(data, msg, thread);
+		if (ret)
+			goto exit_unlock;
+		break;
+	default:
+		ret = -EOPNOTSUPP;
+		goto exit_unlock;
+	}
+
+	/*
+	 * For RMI Rev 0x20, new h/w status bit is introduced. which is used
+	 * by firmware to indicate completion of commands (0x71, 0x72, 0x73).
+	 * wait for the status bit to be set by the hardware before
+	 * reading the data out.
+	 */
+	ret = regmap_read_poll_timeout(data->regmap, SBRMI_STATUS, hw_status,
+				       hw_status & HW_ALERT_MASK, 500, 2000000);
+	if (ret)
+		goto exit_unlock;
+
+	ret = regmap_bulk_read(data->regmap, CPUID_MCA_CMD,
+			       &output, MSR_RD_REG_LEN);
+	if (ret < 0)
+		goto exit_unlock;
+
+	ret = regmap_write(data->regmap, SBRMI_STATUS,
+			   HW_ALERT_MASK);
+	if (ret < 0)
+		goto exit_unlock;
+
+	if (output.num_bytes != MSR_RD_REG_LEN - 1) {
+		ret = -EMSGSIZE;
+		goto exit_unlock;
+	}
+	if (output.status) {
+		ret = -EPROTOTYPE;
+		msg->fw_ret_code = output.status;
+		goto exit_unlock;
+	}
+	msg->mcamsr_in_out = output.value;
+
+exit_unlock:
+	mutex_unlock(&data->lock);
+	return ret;
+}
+
+int rmi_mailbox_xfer(struct sbrmi_data *data,
+		     struct apml_mbox_msg *msg)
+{
+	unsigned int bytes, ec;
+	int i, ret;
+	int sw_status;
+	u8 byte;
+
+	mutex_lock(&data->lock);
+
+	msg->fw_ret_code = 0;
+
+	/* Indicate firmware a command is to be serviced */
+	ret = regmap_write(data->regmap, SBRMI_INBNDMSG7, START_CMD);
+	if (ret < 0)
+		goto exit_unlock;
+
+	/* Write the command to SBRMI::InBndMsg_inst0 */
+	ret = regmap_write(data->regmap, SBRMI_INBNDMSG0, msg->cmd);
+	if (ret < 0)
+		goto exit_unlock;
+
+	/*
+	 * For both read and write the initiator (BMC) writes
+	 * Command Data In[31:0] to SBRMI::InBndMsg_inst[4:1]
+	 * SBRMI_x3C(MSB):SBRMI_x39(LSB)
+	 */
+	for (i = 0; i < AMD_SBI_MB_DATA_SIZE; i++) {
+		byte = (msg->mb_in_out >> i * 8) & 0xff;
+		ret = regmap_write(data->regmap, SBRMI_INBNDMSG1 + i, byte);
+		if (ret < 0)
+			goto exit_unlock;
+	}
+
+	/*
+	 * Write 0x01 to SBRMI::SoftwareInterrupt to notify firmware to
+	 * perform the requested read or write command
+	 */
+	ret = regmap_write(data->regmap, SBRMI_SW_INTERRUPT, TRIGGER_MAILBOX);
+	if (ret < 0)
+		goto exit_unlock;
+
+	/*
+	 * Firmware will write SBRMI::Status[SwAlertSts]=1 to generate
+	 * an ALERT (if enabled) to initiator (BMC) to indicate completion
+	 * of the requested command
+	 */
+	ret = regmap_read_poll_timeout(data->regmap, SBRMI_STATUS, sw_status,
+				       sw_status & SW_ALERT_MASK, 500, 2000000);
+	if (ret)
+		goto exit_unlock;
+
+	ret = regmap_read(data->regmap, SBRMI_OUTBNDMSG7, &ec);
+	if (ret || ec)
+		goto exit_clear_alert;
+
+	/* Clear the input value before updating the output data */
+	msg->mb_in_out = 0;
+
+	/*
+	 * For a read operation, the initiator (BMC) reads the firmware
+	 * response Command Data Out[31:0] from SBRMI::OutBndMsg_inst[4:1]
+	 * {SBRMI_x34(MSB):SBRMI_x31(LSB)}.
+	 */
+	for (i = 0; i < AMD_SBI_MB_DATA_SIZE; i++) {
+		ret = regmap_read(data->regmap,
+				  SBRMI_OUTBNDMSG1 + i, &bytes);
+		if (ret < 0)
+			break;
+		msg->mb_in_out |= bytes << i * 8;
+	}
+
+exit_clear_alert:
+	/*
+	 * BMC must write 1'b1 to SBRMI::Status[SwAlertSts] to clear the
+	 * ALERT to initiator
+	 */
+	ret = regmap_write(data->regmap, SBRMI_STATUS,
+			   sw_status | SW_ALERT_MASK);
+	if (ec) {
+		ret = -EPROTOTYPE;
+		msg->fw_ret_code = ec;
+	}
+exit_unlock:
+	mutex_unlock(&data->lock);
+	return ret;
+}
+
+static int apml_rmi_reg_xfer(struct sbrmi_data *data,
+			     struct apml_reg_xfer_msg __user *arg)
+{
+	struct apml_reg_xfer_msg msg = { 0 };
+	unsigned int data_read;
+	int ret;
+
+	/* Copy the structure from user */
+	if (copy_from_user(&msg, arg, sizeof(struct apml_reg_xfer_msg)))
+		return -EFAULT;
+
+	mutex_lock(&data->lock);
+	if (msg.rflag) {
+		ret = regmap_read(data->regmap, msg.reg_addr, &data_read);
+		if (!ret)
+			msg.data_in_out = data_read;
+	} else {
+		ret = regmap_write(data->regmap, msg.reg_addr, msg.data_in_out);
+	}
+
+	mutex_unlock(&data->lock);
+
+	if (msg.rflag && !ret)
+		if (copy_to_user(arg, &msg, sizeof(struct apml_reg_xfer_msg)))
+			return -EFAULT;
+	return ret;
+}
+
+static int apml_mailbox_xfer(struct sbrmi_data *data, struct apml_mbox_msg __user *arg)
+{
+	struct apml_mbox_msg msg = { 0 };
+	int ret;
+
+	/* Copy the structure from user */
+	if (copy_from_user(&msg, arg, sizeof(struct apml_mbox_msg)))
+		return -EFAULT;
+
+	/* Mailbox protocol */
+	ret = rmi_mailbox_xfer(data, &msg);
+	if (ret && ret != -EPROTOTYPE)
+		return ret;
+
+	if (copy_to_user(arg, &msg, sizeof(struct apml_mbox_msg)))
+		return -EFAULT;
+	return ret;
+}
+
+static int apml_cpuid_xfer(struct sbrmi_data *data, struct apml_cpuid_msg __user *arg)
+{
+	struct apml_cpuid_msg msg = { 0 };
+	int ret;
+
+	/* Copy the structure from user */
+	if (copy_from_user(&msg, arg, sizeof(struct apml_cpuid_msg)))
+		return -EFAULT;
+
+	/* CPUID Protocol */
+	ret = rmi_cpuid_read(data, &msg);
+	if (ret && ret != -EPROTOTYPE)
+		return ret;
+
+	if (copy_to_user(arg, &msg, sizeof(struct apml_cpuid_msg)))
+		return -EFAULT;
+	return ret;
+}
+
+static int apml_mcamsr_xfer(struct sbrmi_data *data, struct apml_mcamsr_msg __user *arg)
+{
+	struct apml_mcamsr_msg msg = { 0 };
+	int ret;
+
+	/* Copy the structure from user */
+	if (copy_from_user(&msg, arg, sizeof(struct apml_mcamsr_msg)))
+		return -EFAULT;
+
+	/* MCAMSR Protocol */
+	ret = rmi_mca_msr_read(data, &msg);
+	if (ret && ret != -EPROTOTYPE)
+		return ret;
+
+	if (copy_to_user(arg, &msg, sizeof(struct apml_mcamsr_msg)))
+		return -EFAULT;
+	return ret;
+}
+
+static long sbrmi_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+	struct sbrmi_data *data;
+
+	data = container_of(fp->private_data, struct sbrmi_data, sbrmi_misc_dev);
+	switch (cmd) {
+	case SBRMI_IOCTL_MBOX_CMD:
+		return apml_mailbox_xfer(data, argp);
+	case SBRMI_IOCTL_CPUID_CMD:
+		return apml_cpuid_xfer(data, argp);
+	case SBRMI_IOCTL_MCAMSR_CMD:
+		return apml_mcamsr_xfer(data, argp);
+	case SBRMI_IOCTL_REG_XFER_CMD:
+		return apml_rmi_reg_xfer(data, argp);
+	default:
+		return -ENOTTY;
+	}
+}
+
+static const struct file_operations sbrmi_fops = {
+	.owner		= THIS_MODULE,
+	.unlocked_ioctl	= sbrmi_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+};
+
+int create_misc_rmi_device(struct sbrmi_data *data,
+			   struct device *dev)
+{
+	data->sbrmi_misc_dev.name	= devm_kasprintf(dev,
+							 GFP_KERNEL,
+							 "sbrmi-%x",
+							 data->dev_static_addr);
+	data->sbrmi_misc_dev.minor	= MISC_DYNAMIC_MINOR;
+	data->sbrmi_misc_dev.fops	= &sbrmi_fops;
+	data->sbrmi_misc_dev.parent	= dev;
+	data->sbrmi_misc_dev.nodename	= devm_kasprintf(dev,
+							 GFP_KERNEL,
+							 "sbrmi-%x",
+							 data->dev_static_addr);
+	data->sbrmi_misc_dev.mode	= 0600;
+
+	return misc_register(&data->sbrmi_misc_dev);
+}
diff --git a/drivers/misc/amd-sbi/rmi-core.h b/drivers/misc/amd-sbi/rmi-core.h
new file mode 100644
index 000000000..975ae858e
--- /dev/null
+++ b/drivers/misc/amd-sbi/rmi-core.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2025 Advanced Micro Devices, Inc.
+ */
+
+#ifndef _SBRMI_CORE_H_
+#define _SBRMI_CORE_H_
+
+#include <linux/miscdevice.h>
+#include <linux/mutex.h>
+#include <linux/i2c.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <uapi/misc/amd-apml.h>
+
+/* SB-RMI registers */
+enum sbrmi_reg {
+	SBRMI_REV,
+	SBRMI_CTRL,
+	SBRMI_STATUS,
+	SBRMI_OUTBNDMSG0	= 0x30,
+	SBRMI_OUTBNDMSG1,
+	SBRMI_OUTBNDMSG2,
+	SBRMI_OUTBNDMSG3,
+	SBRMI_OUTBNDMSG4,
+	SBRMI_OUTBNDMSG5,
+	SBRMI_OUTBNDMSG6,
+	SBRMI_OUTBNDMSG7,
+	SBRMI_INBNDMSG0,
+	SBRMI_INBNDMSG1,
+	SBRMI_INBNDMSG2,
+	SBRMI_INBNDMSG3,
+	SBRMI_INBNDMSG4,
+	SBRMI_INBNDMSG5,
+	SBRMI_INBNDMSG6,
+	SBRMI_INBNDMSG7,
+	SBRMI_SW_INTERRUPT,
+	SBRMI_THREAD128CS	= 0x4b,
+};
+
+/*
+ * SB-RMI supports soft mailbox service request to MP1 (power management
+ * firmware) through SBRMI inbound/outbound message registers.
+ * SB-RMI message IDs
+ */
+enum sbrmi_msg_id {
+	SBRMI_READ_PKG_PWR_CONSUMPTION = 0x1,
+	SBRMI_WRITE_PKG_PWR_LIMIT,
+	SBRMI_READ_PKG_PWR_LIMIT,
+	SBRMI_READ_PKG_MAX_PWR_LIMIT,
+};
+
+/* Each client has this additional data */
+struct sbrmi_data {
+	struct miscdevice sbrmi_misc_dev;
+	struct regmap *regmap;
+	/* Mutex locking */
+	struct mutex lock;
+	u32 pwr_limit_max;
+	u8 dev_static_addr;
+	u8 rev;
+};
+
+int rmi_mailbox_xfer(struct sbrmi_data *data, struct apml_mbox_msg *msg);
+#ifdef CONFIG_AMD_SBRMI_HWMON
+int create_hwmon_sensor_device(struct device *dev, struct sbrmi_data *data);
+#else
+static inline int create_hwmon_sensor_device(struct device *dev, struct sbrmi_data *data)
+{
+	return 0;
+}
+#endif
+int create_misc_rmi_device(struct sbrmi_data *data, struct device *dev);
+#endif /*_SBRMI_CORE_H_*/
diff --git a/drivers/misc/amd-sbi/rmi-hwmon.c b/drivers/misc/amd-sbi/rmi-hwmon.c
new file mode 100644
index 000000000..f4f015605
--- /dev/null
+++ b/drivers/misc/amd-sbi/rmi-hwmon.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * rmi-hwmon.c - hwmon sensor support for side band RMI
+ *
+ * Copyright (C) 2025 Advanced Micro Devices, Inc.
+ */
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <uapi/misc/amd-apml.h>
+#include "rmi-core.h"
+
+/* Do not allow setting negative power limit */
+#define SBRMI_PWR_MIN  0
+
+static int sbrmi_read(struct device *dev, enum hwmon_sensor_types type,
+		      u32 attr, int channel, long *val)
+{
+	struct sbrmi_data *data = dev_get_drvdata(dev);
+	struct apml_mbox_msg msg = { 0 };
+	int ret;
+
+	if (!data)
+		return -ENODEV;
+
+	if (type != hwmon_power)
+		return -EINVAL;
+
+	switch (attr) {
+	case hwmon_power_input:
+		msg.cmd = SBRMI_READ_PKG_PWR_CONSUMPTION;
+		ret = rmi_mailbox_xfer(data, &msg);
+		break;
+	case hwmon_power_cap:
+		msg.cmd = SBRMI_READ_PKG_PWR_LIMIT;
+		ret = rmi_mailbox_xfer(data, &msg);
+		break;
+	case hwmon_power_cap_max:
+		msg.mb_in_out = data->pwr_limit_max;
+		ret = 0;
+		break;
+	default:
+		return -EINVAL;
+	}
+	if (ret < 0)
+		return ret;
+	/* hwmon power attributes are in microWatt */
+	*val = (long)msg.mb_in_out * 1000;
+	return ret;
+}
+
+static int sbrmi_write(struct device *dev, enum hwmon_sensor_types type,
+		       u32 attr, int channel, long val)
+{
+	struct sbrmi_data *data = dev_get_drvdata(dev);
+	struct apml_mbox_msg msg = { 0 };
+
+	if (!data)
+		return -ENODEV;
+
+	if (type != hwmon_power && attr != hwmon_power_cap)
+		return -EINVAL;
+	/*
+	 * hwmon power attributes are in microWatt
+	 * mailbox read/write is in mWatt
+	 */
+	val /= 1000;
+
+	val = clamp_val(val, SBRMI_PWR_MIN, data->pwr_limit_max);
+
+	msg.cmd = SBRMI_WRITE_PKG_PWR_LIMIT;
+	msg.mb_in_out = val;
+
+	return rmi_mailbox_xfer(data, &msg);
+}
+
+static umode_t sbrmi_is_visible(const void *data,
+				enum hwmon_sensor_types type,
+				u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_power:
+		switch (attr) {
+		case hwmon_power_input:
+		case hwmon_power_cap_max:
+			return 0444;
+		case hwmon_power_cap:
+			return 0644;
+		}
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+static const struct hwmon_channel_info * const sbrmi_info[] = {
+	HWMON_CHANNEL_INFO(power,
+			   HWMON_P_INPUT | HWMON_P_CAP | HWMON_P_CAP_MAX),
+	NULL
+};
+
+static const struct hwmon_ops sbrmi_hwmon_ops = {
+	.is_visible = sbrmi_is_visible,
+	.read = sbrmi_read,
+	.write = sbrmi_write,
+};
+
+static const struct hwmon_chip_info sbrmi_chip_info = {
+	.ops = &sbrmi_hwmon_ops,
+	.info = sbrmi_info,
+};
+
+int create_hwmon_sensor_device(struct device *dev, struct sbrmi_data *data)
+{
+	struct device *hwmon_dev;
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, "sbrmi", data,
+							 &sbrmi_chip_info, NULL);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
diff --git a/drivers/misc/amd-sbi/rmi-i2c.c b/drivers/misc/amd-sbi/rmi-i2c.c
new file mode 100644
index 000000000..37e5ea83b
--- /dev/null
+++ b/drivers/misc/amd-sbi/rmi-i2c.c
@@ -0,0 +1,247 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * rmi-i2c.c - Side band RMI over I2C support for AMD out
+ *             of band management
+ *
+ * Copyright (C) 2024 Advanced Micro Devices, Inc.
+ */
+
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/i3c/device.h>
+#include <linux/i3c/master.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include "rmi-core.h"
+
+#define REV_TWO_BYTE_ADDR	0x21
+
+static int sbrmi_enable_alert(struct sbrmi_data *data)
+{
+	int ctrl, ret;
+
+	/*
+	 * Enable the SB-RMI Software alert status
+	 * by writing 0 to bit 4 of Control register(0x1)
+	 */
+	ret = regmap_read(data->regmap, SBRMI_CTRL, &ctrl);
+	if (ret < 0)
+		return ret;
+
+	if (ctrl & 0x10) {
+		ctrl &= ~0x10;
+		return regmap_write(data->regmap, SBRMI_CTRL, ctrl);
+	}
+
+	return 0;
+}
+
+static int sbrmi_get_max_pwr_limit(struct sbrmi_data *data)
+{
+	struct apml_mbox_msg msg = { 0 };
+	int ret;
+
+	msg.cmd = SBRMI_READ_PKG_MAX_PWR_LIMIT;
+	ret = rmi_mailbox_xfer(data, &msg);
+	if (ret < 0)
+		return ret;
+	data->pwr_limit_max = msg.mb_in_out;
+
+	return ret;
+}
+
+static int sbrmi_common_probe(struct device *dev, struct regmap *regmap, uint8_t address)
+{
+	struct sbrmi_data *data;
+	int ret;
+
+	data = devm_kzalloc(dev, sizeof(struct sbrmi_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = regmap;
+	mutex_init(&data->lock);
+
+	/* Enable alert for SB-RMI sequence */
+	ret = sbrmi_enable_alert(data);
+	if (ret < 0)
+		return ret;
+
+	/* Cache maximum power limit */
+	ret = sbrmi_get_max_pwr_limit(data);
+	if (ret < 0)
+		return ret;
+
+	data->dev_static_addr = address;
+
+	dev_set_drvdata(dev, data);
+
+	ret = create_hwmon_sensor_device(dev, data);
+	if (ret < 0)
+		return ret;
+	return create_misc_rmi_device(data, dev);
+}
+
+static struct regmap_config sbrmi_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static struct regmap_config sbrmi_regmap_config_ext = {
+	.reg_bits = 16,
+	.val_bits = 8,
+	.reg_format_endian = REGMAP_ENDIAN_LITTLE,
+};
+
+static int sbrmi_i2c_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct regmap *regmap;
+	int rev, ret;
+
+	regmap = devm_regmap_init_i2c(client, &sbrmi_regmap_config);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	ret = regmap_read(regmap, SBRMI_REV, &rev);
+	if (ret)
+		return ret;
+
+	/*
+	 * For Turin and newer platforms, revision is 0x21 or later. This is
+	 * to identify the two byte register address size. However, one
+	 * byte transaction can be successful.
+	 * Verify if revision is 0x21 or later, if yes, switch to 2 byte
+	 * address size.
+	 * Continuously using 1 byte address for revision 0x21 or later can lead
+	 * to bus corruption.
+	 */
+	if (rev >= REV_TWO_BYTE_ADDR) {
+		regmap = devm_regmap_init_i2c(client, &sbrmi_regmap_config_ext);
+		if (IS_ERR(regmap))
+			return PTR_ERR(regmap);
+	}
+	return sbrmi_common_probe(dev, regmap, client->addr);
+}
+
+static void sbrmi_i2c_remove(struct i2c_client *client)
+{
+	struct sbrmi_data *data = dev_get_drvdata(&client->dev);
+
+	misc_deregister(&data->sbrmi_misc_dev);
+	/* Assign fops and parent of misc dev to NULL */
+	data->sbrmi_misc_dev.fops = NULL;
+	data->sbrmi_misc_dev.parent = NULL;
+	dev_info(&client->dev, "Removed sbrmi-i2c driver\n");
+	return;
+}
+
+static const struct i2c_device_id sbrmi_id[] = {
+	{"sbrmi-i2c"},
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, sbrmi_id);
+
+static const struct of_device_id __maybe_unused sbrmi_of_match[] = {
+	{
+		.compatible = "amd,sbrmi",
+	},
+	{ },
+};
+MODULE_DEVICE_TABLE(of, sbrmi_of_match);
+
+static struct i2c_driver sbrmi_driver = {
+	.driver = {
+		.name = "sbrmi-i2c",
+		.of_match_table = of_match_ptr(sbrmi_of_match),
+	},
+	.probe = sbrmi_i2c_probe,
+	.remove = sbrmi_i2c_remove,
+	.id_table = sbrmi_id,
+};
+
+static int sbrmi_i3c_probe(struct i3c_device *i3cdev)
+{
+	struct device *dev = i3cdev_to_dev(i3cdev);
+	struct regmap *regmap;
+	int rev, ret;
+
+	/*
+	 * AMD OOB devices are distinguished by their Instance ID.
+	 * For SBRMI, the Instance ID is 1. Since the device ID match
+	 * does not account for the Instance ID, the following check
+	 * ensures that only the SBRMI device is probed, excluding
+	 * other OOB devices.
+	 */
+	if (I3C_PID_INSTANCE_ID(i3cdev->desc->info.pid) != 1)
+		return -ENXIO;
+
+	regmap = devm_regmap_init_i3c(i3cdev, &sbrmi_regmap_config);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	ret = regmap_read(regmap, SBRMI_REV, &rev);
+	if (ret)
+		return ret;
+
+	/*
+	 * For Turin and newer platforms, revision is 0x21 or later. This is
+	 * to identify the two byte register address size. However, one
+	 * byte transaction can be successful.
+	 * Verify if revision is 0x21 or later, if yes, switch to 2 byte
+	 * address size.
+	 * Continuously using 1 byte address for revision 0x21 or later can lead
+	 * to bus corruption.
+	 */
+	if (rev >= REV_TWO_BYTE_ADDR) {
+		regmap = devm_regmap_init_i3c(i3cdev, &sbrmi_regmap_config_ext);
+		if (IS_ERR(regmap))
+			return PTR_ERR(regmap);
+	}
+
+	/*
+	 * AMD APML I3C devices support static address.
+	 * If static address is defined, dynamic address is same as static address.
+	 * In case static address is not defined, I3C master controller defined
+	 * dynamic address is used.
+	 */
+	return sbrmi_common_probe(dev, regmap, i3cdev->desc->info.dyn_addr);
+}
+
+static void sbrmi_i3c_remove(struct i3c_device *i3cdev)
+{
+	struct sbrmi_data *data = dev_get_drvdata(&i3cdev->dev);
+
+	misc_deregister(&data->sbrmi_misc_dev);
+}
+
+static const struct i3c_device_id sbrmi_i3c_id[] = {
+	/* PID for AMD SBRMI device */
+	I3C_DEVICE_EXTRA_INFO(0x112, 0x0, 0x2, NULL),
+	I3C_DEVICE_EXTRA_INFO(0x0, 0x0, 0x118, NULL), /* Socket:0, Venice */
+	I3C_DEVICE_EXTRA_INFO(0x0, 0x100, 0x118, NULL), /* Socket:1, Venice */
+	I3C_DEVICE_EXTRA_INFO(0x112, 0x0, 0x119, NULL), /* Socket:0, Venice */
+	I3C_DEVICE_EXTRA_INFO(0x112, 0x100, 0x119, NULL), /* Socket:1, Venice */
+	{}
+};
+MODULE_DEVICE_TABLE(i3c, sbrmi_i3c_id);
+
+static struct i3c_driver sbrmi_i3c_driver = {
+	.driver = {
+		.name = "sbrmi-i3c",
+	},
+	.probe = sbrmi_i3c_probe,
+	.remove = sbrmi_i3c_remove,
+	.id_table = sbrmi_i3c_id,
+};
+
+module_i3c_i2c_driver(sbrmi_i3c_driver, &sbrmi_driver);
+
+MODULE_AUTHOR("Akshay Gupta <akshay.gupta@amd.com>");
+MODULE_AUTHOR("Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>");
+MODULE_DESCRIPTION("Hwmon driver for AMD SB-RMI emulated sensor");
+MODULE_LICENSE("GPL");