[PATCH v3 0/4] hwmon: Add Kandou KB9002 PCIe retimer driver

[PATCH v3 0/4] hwmon: Add Kandou KB9002 PCIe retimer driver

[Andy Chung via B4 Relay]

The Kandou KB9002 is an 8-lane PCIe 5.0 retimer with an integrated
microcontroller that exposes an SMBus 3.0 target (with mandatory PEC)
on its sideband interface. Its firmware aggregates per-lane die
temperatures and publishes the maximum through a register window.

This series adds a hwmon driver for it. The driver reports the
aggregated maximum die temperature as temp1_input, and exposes the
running firmware version and boot status under debugfs.

The series is organised as:

  1/4  add the "kandou" vendor prefix
  2/4  device tree binding for the retimer
  3/4  the driver, Kconfig/Makefile and MAINTAINERS entry
  4/4  hwmon documentation

Signed-off-by: Andy Chung <Andy.Chung@amd.com>
---
Changes in v3:
- Drop the private register-access mutex. The temperature read is
  already serialised by the hwmon core lock; the debugfs files
  (fw_ver, fw_load_status) now take hwmon_lock() to serialise
  against it, since they are read outside the core lock.
- Use a named initialiser for the i2c_device_id entry.
- dt-bindings: constrain the reg address range under 'items' rather
  than applying minimum/maximum to the array.
- Link to v2: https://patch.msgid.link/20260715-kb9002-upstream-v2-0-2fd390383da5@amd.com

Changes in v2:
- Drop the unconditional I2C_FUNC_I2C requirement at probe; require raw
  I2C only in the host-interface switch path, so the driver loads on
  SMBus-only adapters when the chip is already strapped to SMBus.
- kb9002_read_revid(): return immediately on a hard I2C read error
  instead of retrying the FIFO drain, avoiding needless bus traffic when
  the device is absent.
- Link to v1: https://lore.kernel.org/all/20260714-kb9002-upstream-v1-0-8fd2f0b135d8@amd.com

---
Andy Chung (4):
      dt-bindings: Add vendor prefix for Kandou
      dt-bindings: hwmon: Add Kandou KB9002
      hwmon: (kb9002) Add driver for Kandou KB9002 retimer
      hwmon: (kb9002) Add documentation

 .../devicetree/bindings/hwmon/kandou,kb9002.yaml   |  46 ++
 .../devicetree/bindings/vendor-prefixes.yaml       |   2 +
 Documentation/hwmon/index.rst                      |   1 +
 Documentation/hwmon/kb9002.rst                     |  65 +++
 MAINTAINERS                                        |   8 +
 drivers/hwmon/Kconfig                              |  11 +
 drivers/hwmon/Makefile                             |   1 +
 drivers/hwmon/kb9002.c                             | 469 +++++++++++++++++++++
 8 files changed, 603 insertions(+)
---
base-commit: ca078d004cf58137bcf8cb24a8b271397431ba58
change-id: 20260713-kb9002-upstream-06c686e37833

Best regards,
--  
Andy Chung <Andy.Chung@amd.com>

[PATCH v3 1/4] dt-bindings: Add vendor prefix for Kandou

[Andy Chung via B4 Relay]

From: Andy Chung <Andy.Chung@amd.com>

Kandou Bus, S.A. is the vendor of the KB9002 PCIe retimer.

Signed-off-by: Andy Chung <Andy.Chung@amd.com>
---
 Documentation/devicetree/bindings/vendor-prefixes.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/vendor-prefixes.yaml b/Documentation/devicetree/bindings/vendor-prefixes.yaml
index 396044f368e7..727871970d97 100644
--- a/Documentation/devicetree/bindings/vendor-prefixes.yaml
+++ b/Documentation/devicetree/bindings/vendor-prefixes.yaml
@@ -879,6 +879,8 @@ patternProperties:
     description: JuTouch Technology Co., Ltd.
   "^kam,.*":
     description: Kamstrup A/S
+  "^kandou,.*":
+    description: Kandou Bus, S.A.
   "^karo,.*":
     description: Ka-Ro electronics GmbH
   "^keithkoep,.*":

-- 
2.34.1

Re: [PATCH v3 1/4] dt-bindings: Add vendor prefix for Kandou

[Krzysztof Kozlowski]

On 21/07/2026 08:31, Andy Chung via B4 Relay wrote:
> From: Andy Chung <Andy.Chung@amd.com>
> 
> Kandou Bus, S.A. is the vendor of the KB9002 PCIe retimer.
> 
> Signed-off-by: Andy Chung <Andy.Chung@amd.com>
> ---

Bad timing, I replied under v2.

Best regards,
Krzysztof

[PATCH v3 2/4] dt-bindings: hwmon: Add Kandou KB9002

[Andy Chung via B4 Relay]

From: Andy Chung <Andy.Chung@amd.com>

Add device tree bindings for the Kandou KB9002 PCIe 5.0 retimer, an
SMBus target that exposes an aggregated die temperature.

Signed-off-by: Andy Chung <Andy.Chung@amd.com>
---
 .../devicetree/bindings/hwmon/kandou,kb9002.yaml   | 46 ++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/Documentation/devicetree/bindings/hwmon/kandou,kb9002.yaml b/Documentation/devicetree/bindings/hwmon/kandou,kb9002.yaml
new file mode 100644
index 000000000000..0d939c8aa734
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/kandou,kb9002.yaml
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/hwmon/kandou,kb9002.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Kandou KB9002 PCIe 5.0 retimer
+
+maintainers:
+  - Andy Chung <andy.chung@amd.com>
+
+description: |
+  The Kandou KB9002 is an 8-lane PCIe 5.0 retimer that exposes a
+  firmware-controlled SMBus 3.0 target on its sideband interface.
+  The host can query the aggregated maximum die temperature and the
+  running firmware version through that target.
+
+  The 7-bit SMBus address is selected by three SMB_ADDR straps and
+  ranges from 0x20 to 0x27.
+
+properties:
+  compatible:
+    const: kandou,kb9002
+
+  reg:
+    items:
+      - minimum: 0x20
+        maximum: 0x27
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        retimer@20 {
+            compatible = "kandou,kb9002";
+            reg = <0x20>;
+        };
+    };

-- 
2.34.1

Re: [PATCH v3 2/4] dt-bindings: hwmon: Add Kandou KB9002

[Krzysztof Kozlowski]

On Tue, Jul 21, 2026 at 02:31:33PM +0800, Andy Chung wrote:
> Add device tree bindings for the Kandou KB9002 PCIe 5.0 retimer, an
> SMBus target that exposes an aggregated die temperature.
> 
> Signed-off-by: Andy Chung <Andy.Chung@amd.com>
> ---
>  .../devicetree/bindings/hwmon/kandou,kb9002.yaml   | 46 ++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
>

So a trivial device and can go to trivial-devices? What is incomplete
here, what is missing?

Best regards,
Krzysztof

Re: [PATCH v3 2/4] dt-bindings: hwmon: Add Kandou KB9002

[Andy Chung]

On Wed, 22 Jul 2026 09:41:29 +0200, Krzysztof Kozlowski wrote:
> So a trivial device and can go to trivial-devices? What is incomplete
> here, what is missing?

Right, nothing beyond compatible and reg. v5 drops the dedicated binding
and adds kandou,kb9002 to trivial-devices.yaml. I also changed the
vendor-prefix description to "Kandou AI" per your other comment
("Kandou Bus SA" is the registered legal entity, "Kandou AI" the current
branding -- same company).

Thanks,
Andy

[PATCH v3 3/4] hwmon: (kb9002) Add driver for Kandou KB9002 retimer

[Andy Chung via B4 Relay]

From: Andy Chung <Andy.Chung@amd.com>

The Kandou KB9002 is an 8-lane PCIe 5.0 retimer that exposes an SMBus
target with mandatory PEC. Add a hwmon driver reporting the firmware
aggregated maximum die temperature as temp1_input, with the firmware
version and boot status under debugfs.

Signed-off-by: Andy Chung <Andy.Chung@amd.com>
---
 MAINTAINERS            |   8 +
 drivers/hwmon/Kconfig  |  11 ++
 drivers/hwmon/Makefile |   1 +
 drivers/hwmon/kb9002.c | 469 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 489 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 9b4b1575bdbd..1d80ac2660e2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13931,6 +13931,14 @@ S:	Maintained
 F:	Documentation/hwmon/k8temp.rst
 F:	drivers/hwmon/k8temp.c
 
+KANDOU KB9002 PCIE RETIMER HWMON DRIVER
+M:	Andy Chung <andy.chung@amd.com>
+L:	linux-hwmon@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/hwmon/kandou,kb9002.yaml
+F:	Documentation/hwmon/kb9002.rst
+F:	drivers/hwmon/kb9002.c
+
 KASAN
 M:	Andrey Ryabinin <ryabinin.a.a@gmail.com>
 R:	Alexander Potapenko <glider@google.com>
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 08c29685126a..300329773e87 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -335,6 +335,17 @@ config SENSORS_K10TEMP
 	  This driver can also be built as a module. If so, the module
 	  will be called k10temp.
 
+config SENSORS_KB9002
+	tristate "Kandou KB9002 PCIe retimer"
+	depends on I2C
+	help
+	  If you say yes here you get support for the integrated
+	  temperature sensor and firmware version readout on Kandou
+	  KB9002 PCIe 5.0 retimers, accessed over SMBus.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called kb9002.
+
 config SENSORS_KBATT
 	tristate "KEBA battery controller support"
 	depends on KEBA_CP500
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 63809eeec2f4..0cad7e21634c 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -113,6 +113,7 @@ obj-$(CONFIG_SENSORS_IT87)	+= it87.o
 obj-$(CONFIG_SENSORS_JC42)	+= jc42.o
 obj-$(CONFIG_SENSORS_K8TEMP)	+= k8temp.o
 obj-$(CONFIG_SENSORS_K10TEMP)	+= k10temp.o
+obj-$(CONFIG_SENSORS_KB9002)	+= kb9002.o
 obj-$(CONFIG_SENSORS_KBATT)	+= kbatt.o
 obj-$(CONFIG_SENSORS_KFAN)	+= kfan.o
 obj-$(CONFIG_SENSORS_LAN966X)	+= lan966x-hwmon.o
diff --git a/drivers/hwmon/kb9002.c b/drivers/hwmon/kb9002.c
new file mode 100644
index 000000000000..61a6e522e770
--- /dev/null
+++ b/drivers/hwmon/kb9002.c
@@ -0,0 +1,469 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Kandou KB9002 PCIe 5.0 retimer hwmon driver.
+ *
+ * The retimer exposes a system management bus (SMBus 3.0 with PEC)
+ * target for firmware-managed status registers. This driver assumes
+ * the chip is strapped to SMBus mode and exports the aggregated
+ * maximum die temperature as hwmon temp1_input (millidegrees Celsius)
+ * plus the firmware version and boot status under debugfs.
+ *
+ * Datasheet: Kandou KB9002 PCIe retimer (KA-015171-PD).
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bitops.h>
+#include <linux/cleanup.h>
+#include <linux/debugfs.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/i2c.h>
+#include <linux/iopoll.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/seq_file.h>
+#include <linux/types.h>
+#include <linux/unaligned.h>
+
+#define KB9002_DEV_NAME			"kb9002"
+
+/*
+ * SMBus read command codes. Each read is a two-phase PEC-protected
+ * transaction: prime writes the target address, data reads it back with
+ * the register contents. FW reads use a 16-bit address, HW reads 32-bit.
+ */
+#define KB9002_CC_FW_READ_PRIME		0x82
+#define KB9002_CC_FW_READ_DATA		0x81
+#define KB9002_CC_HW_READ_PRIME		0x8a
+#define KB9002_CC_HW_READ_DATA		0x89
+
+/* Firmware register offsets (16-bit). */
+#define KB9002_FW_REG_VID		0x0004
+#define KB9002_FW_REG_FW_VERSION	0x0500
+#define KB9002_FW_REG_TEMP_MAXIMUM	0x0550
+
+#define KB9002_VID_MASK			GENMASK(31, 16)
+#define KB9002_VID_KANDOU		0x1e6f
+
+/* Firmware boot status: 0xe8 in the top byte means init completed OK. */
+#define KB9002_HW_REG_FW_BOOT_STATUS	0xe0090008
+#define KB9002_FW_BOOT_STATUS_OK_MSB	0xe8
+
+/*
+ * Hardware registers reached over raw I2C (32-bit addressing). The
+ * host-interface bit selects SMBus (set) vs raw-I2C target; parts
+ * strapped to raw I2C need it set before SMBus access works.
+ */
+#define KB9002_HW_REG_REVID		0x00480004
+#define KB9002_HW_REG_HOST_IF		0x00480008
+#define KB9002_HOST_IF_SMBUS		BIT(1)
+
+#define KB9002_REVID_MASK		GENMASK(7, 0)
+#define KB9002_REVID_B0			0x10
+#define KB9002_REVID_B1			0x11
+
+/* Retries to drain a stray leading 0xff from the raw-I2C FIFO. */
+#define KB9002_REVID_READ_RETRIES	16
+
+/* Temperature: 32-bit Q16.16 absolute Kelvin. */
+#define KB9002_TEMP_FRAC_BITS		16
+#define KB9002_ABS_ZERO_MILLI_C		(-273150)
+
+/* Firmware takes up to ~2s to respond after a host-interface change. */
+#define KB9002_FW_READY_POLL_US		(25 * USEC_PER_MSEC)
+#define KB9002_FW_READY_TIMEOUT_US	(2 * USEC_PER_SEC)
+
+struct kb9002_data {
+	struct i2c_client *client;
+	struct device *hwmon_dev;
+};
+
+/* Raw-I2C read: write the 32-bit BE address, then read 4 BE data bytes. */
+static int kb9002_i2c_read(struct i2c_client *client, u32 reg, u32 *val)
+{
+	u8 addr[4];
+	u8 rbuf[4];
+	struct i2c_msg msgs[2] = {
+		{
+			.addr = client->addr,
+			.flags = 0,
+			.len = sizeof(addr),
+			.buf = addr,
+		},
+		{
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.len = sizeof(rbuf),
+			.buf = rbuf,
+		},
+	};
+	int ret;
+
+	put_unaligned_be32(reg, addr);
+
+	ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (ret < 0)
+		return ret;
+	if (ret != ARRAY_SIZE(msgs))
+		return -EIO;
+
+	*val = get_unaligned_be32(rbuf);
+	return 0;
+}
+
+/* Raw-I2C write: 4 BE address bytes followed by 4 BE data bytes. */
+static int kb9002_i2c_write(struct i2c_client *client, u32 reg, u32 val)
+{
+	u8 buf[8];
+	struct i2c_msg msg = {
+		.addr = client->addr,
+		.flags = 0,
+		.len = sizeof(buf),
+		.buf = buf,
+	};
+	int ret;
+
+	put_unaligned_be32(reg, &buf[0]);
+	put_unaligned_be32(val, &buf[4]);
+
+	ret = i2c_transfer(client->adapter, &msg, 1);
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EIO;
+
+	return 0;
+}
+
+/*
+ * Read the silicon revision ID. A fresh FIFO may start with a stray
+ * 0xff that shifts the result, so drain one byte between retries until
+ * the top byte is no longer 0xff.
+ */
+static int kb9002_read_revid(struct i2c_client *client, u32 *revid)
+{
+	u8 dummy;
+	int ret;
+	int i;
+
+	for (i = 0; i < KB9002_REVID_READ_RETRIES; i++) {
+		ret = kb9002_i2c_read(client, KB9002_HW_REG_REVID, revid);
+		if (ret)
+			return ret;
+		if ((*revid >> 24) != 0xff)
+			return 0;
+		/* Drain one byte from the chip to re-align the I2C FIFO. */
+		i2c_master_recv(client, &dummy, 1);
+	}
+
+	return -EIO;
+}
+
+/*
+ * Read a 32-bit firmware register over SMBus: block-write the 16-bit LE
+ * address, then block-read the echoed address plus 4 LE data bytes.
+ */
+static int kb9002_fw_read(struct kb9002_data *data, u16 reg, u32 *val)
+{
+	struct i2c_client *client = data->client;
+	u8 addr[2];
+	u8 rbuf[I2C_SMBUS_BLOCK_MAX];
+	int ret;
+
+	put_unaligned_le16(reg, addr);
+
+	ret = i2c_smbus_write_block_data(client, KB9002_CC_FW_READ_PRIME,
+					 sizeof(addr), addr);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_read_block_data(client, KB9002_CC_FW_READ_DATA, rbuf);
+	if (ret < 0)
+		return ret;
+	if (ret < (int)(sizeof(addr) + sizeof(*val)))
+		return -EIO;
+
+	*val = get_unaligned_le32(&rbuf[sizeof(addr)]);
+	return 0;
+}
+
+/* Like kb9002_fw_read but for a hardware register (32-bit LE address). */
+static int kb9002_smbus_hw_read(struct kb9002_data *data, u32 reg, u32 *val)
+{
+	struct i2c_client *client = data->client;
+	u8 addr[4];
+	u8 rbuf[I2C_SMBUS_BLOCK_MAX];
+	int ret;
+
+	put_unaligned_le32(reg, addr);
+
+	ret = i2c_smbus_write_block_data(client, KB9002_CC_HW_READ_PRIME,
+					 sizeof(addr), addr);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_read_block_data(client, KB9002_CC_HW_READ_DATA, rbuf);
+	if (ret < 0)
+		return ret;
+	if (ret < (int)(sizeof(addr) + sizeof(*val)))
+		return -EIO;
+
+	*val = get_unaligned_le32(&rbuf[sizeof(addr)]);
+	return 0;
+}
+
+/*
+ * Switch the host interface from raw-I2C to SMBus and wait for firmware
+ * to come back up. Called only when SMBus access failed in probe, i.e.
+ * the chip is strapped to raw-I2C mode. Confirms the revision, sets the
+ * SMBus-mode bit, then polls until firmware responds again.
+ */
+static int kb9002_enable_smbus_target(struct kb9002_data *data)
+{
+	struct i2c_client *client = data->client;
+	u32 revid;
+	u32 val;
+	int op_ret;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return dev_err_probe(&client->dev, -ENODEV,
+				     "raw I2C required to switch to SMBus mode\n");
+
+	ret = kb9002_read_revid(client, &revid);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "revision ID read failed\n");
+
+	switch (FIELD_GET(KB9002_REVID_MASK, revid)) {
+	case KB9002_REVID_B0:
+	case KB9002_REVID_B1:
+		break;
+	default:
+		return dev_err_probe(&client->dev, -ENODEV,
+				     "unsupported revision ID 0x%08x\n", revid);
+	}
+
+	ret = kb9002_i2c_read(client, KB9002_HW_REG_HOST_IF, &val);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "host interface read failed\n");
+
+	val |= KB9002_HOST_IF_SMBUS;
+
+	ret = kb9002_i2c_write(client, KB9002_HW_REG_HOST_IF, val);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "host interface write failed\n");
+
+	/* Wait until firmware re-initialisation completes. */
+	ret = read_poll_timeout(kb9002_fw_read, op_ret, op_ret == 0,
+				KB9002_FW_READY_POLL_US,
+				KB9002_FW_READY_TIMEOUT_US, true,
+				data, KB9002_FW_REG_VID, &val);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "firmware not responding over SMBus\n");
+
+	return 0;
+}
+
+/* Convert Q16.16 absolute Kelvin to millidegrees Celsius. */
+static long kb9002_temp_to_milli_c(u32 raw)
+{
+	s64 milli_k = ((s64)raw * 1000) >> KB9002_TEMP_FRAC_BITS;
+
+	return (long)milli_k + KB9002_ABS_ZERO_MILLI_C;
+}
+
+static int kb9002_read_temp(struct kb9002_data *data, long *val)
+{
+	u32 raw;
+	int ret;
+
+	ret = kb9002_fw_read(data, KB9002_FW_REG_TEMP_MAXIMUM, &raw);
+	if (ret)
+		return ret;
+
+	*val = kb9002_temp_to_milli_c(raw);
+	return 0;
+}
+
+static umode_t kb9002_is_visible(const void *drvdata,
+				 enum hwmon_sensor_types type,
+				 u32 attr, int channel)
+{
+	if (type == hwmon_temp &&
+	    (attr == hwmon_temp_input || attr == hwmon_temp_label))
+		return 0444;
+	return 0;
+}
+
+static int kb9002_read(struct device *dev, enum hwmon_sensor_types type,
+		       u32 attr, int channel, long *val)
+{
+	struct kb9002_data *data = dev_get_drvdata(dev);
+
+	if (type == hwmon_temp && attr == hwmon_temp_input)
+		return kb9002_read_temp(data, val);
+
+	return -EOPNOTSUPP;
+}
+
+static int kb9002_read_string(struct device *dev, enum hwmon_sensor_types type,
+			      u32 attr, int channel, const char **str)
+{
+	if (type == hwmon_temp && attr == hwmon_temp_label) {
+		*str = KB9002_DEV_NAME;
+		return 0;
+	}
+	return -EOPNOTSUPP;
+}
+
+static const struct hwmon_ops kb9002_hwmon_ops = {
+	.is_visible = kb9002_is_visible,
+	.read = kb9002_read,
+	.read_string = kb9002_read_string,
+};
+
+static const struct hwmon_channel_info * const kb9002_hwmon_info[] = {
+	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT | HWMON_T_LABEL),
+	NULL,
+};
+
+static const struct hwmon_chip_info kb9002_chip_info = {
+	.ops = &kb9002_hwmon_ops,
+	.info = kb9002_hwmon_info,
+};
+
+static int kb9002_fw_version_show(struct seq_file *s, void *unused)
+{
+	struct kb9002_data *data = s->private;
+	u32 ver;
+	int ret;
+
+	guard(hwmon_lock)(data->hwmon_dev);
+
+	ret = kb9002_fw_read(data, KB9002_FW_REG_FW_VERSION, &ver);
+	if (ret)
+		return ret;
+
+	seq_printf(s, "%u.%02u.%02u.%u\n",
+		   (ver >> 24) & 0xff, (ver >> 16) & 0xff,
+		   (ver >>  8) & 0xff, (ver >>  0) & 0xff);
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(kb9002_fw_version);
+
+static int kb9002_fw_load_status_show(struct seq_file *s, void *unused)
+{
+	struct kb9002_data *data = s->private;
+	u32 status;
+	int ret;
+
+	guard(hwmon_lock)(data->hwmon_dev);
+
+	ret = kb9002_smbus_hw_read(data, KB9002_HW_REG_FW_BOOT_STATUS, &status);
+	if (ret)
+		return ret;
+
+	seq_printf(s, "%s\n",
+		   (status >> 24) == KB9002_FW_BOOT_STATUS_OK_MSB ?
+		   "normal" : "abnormal");
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(kb9002_fw_load_status);
+
+static void kb9002_debugfs_init(struct kb9002_data *data)
+{
+	struct dentry *dir = data->client->debugfs;
+
+	debugfs_create_file("fw_ver", 0444, dir, data,
+			    &kb9002_fw_version_fops);
+	debugfs_create_file("fw_load_status", 0444, dir, data,
+			    &kb9002_fw_load_status_fops);
+}
+
+static int kb9002_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct kb9002_data *data;
+	struct device *hwmon_dev;
+	u32 vid;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_BLOCK_DATA |
+				     I2C_FUNC_SMBUS_PEC))
+		return -ENODEV;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+
+	/* All firmware register accesses are PEC-protected. */
+	client->flags |= I2C_CLIENT_PEC;
+
+	i2c_set_clientdata(client, data);
+
+	/*
+	 * Try SMBus first. If the chip is strapped to raw-I2C mode it
+	 * will not respond to SMBus framing, so fall back to switching
+	 * the host interface over raw I2C and retry.
+	 */
+	ret = kb9002_fw_read(data, KB9002_FW_REG_VID, &vid);
+	if (ret) {
+		dev_dbg(dev, "SMBus probe failed (%d), trying raw-I2C host-interface switch\n",
+			ret);
+		ret = kb9002_enable_smbus_target(data);
+		if (ret)
+			return ret;
+		ret = kb9002_fw_read(data, KB9002_FW_REG_VID, &vid);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "VID read failed after host-interface switch\n");
+	}
+	if (FIELD_GET(KB9002_VID_MASK, vid) != KB9002_VID_KANDOU)
+		return dev_err_probe(dev, -ENODEV,
+				     "unexpected VID 0x%08x\n", vid);
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, KB9002_DEV_NAME,
+							 data,
+							 &kb9002_chip_info,
+							 NULL);
+	if (IS_ERR(hwmon_dev))
+		return PTR_ERR(hwmon_dev);
+
+	data->hwmon_dev = hwmon_dev;
+	kb9002_debugfs_init(data);
+	return 0;
+}
+
+static const struct i2c_device_id kb9002_id[] = {
+	{ .name = KB9002_DEV_NAME },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, kb9002_id);
+
+static const struct of_device_id kb9002_of_match[] = {
+	{ .compatible = "kandou,kb9002" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, kb9002_of_match);
+
+static struct i2c_driver kb9002_driver = {
+	.driver = {
+		.name = KB9002_DEV_NAME,
+		.of_match_table = kb9002_of_match,
+	},
+	.probe = kb9002_probe,
+	.id_table = kb9002_id,
+};
+module_i2c_driver(kb9002_driver);
+
+MODULE_AUTHOR("Andy Chung <andy.chung@amd.com>");
+MODULE_DESCRIPTION("Kandou KB9002 PCIe retimer hwmon driver");
+MODULE_LICENSE("GPL");

-- 
2.34.1

Re: [PATCH v3 3/4] hwmon: (kb9002) Add driver for Kandou KB9002 retimer

[Guenter Roeck]

On 7/20/26 23:31, Andy Chung via B4 Relay wrote:
> From: Andy Chung <Andy.Chung@amd.com>
> 
> The Kandou KB9002 is an 8-lane PCIe 5.0 retimer that exposes an SMBus
> target with mandatory PEC. Add a hwmon driver reporting the firmware
> aggregated maximum die temperature as temp1_input, with the firmware
> version and boot status under debugfs.
> 
> Signed-off-by: Andy Chung <Andy.Chung@amd.com>
> ---
>   MAINTAINERS            |   8 +
>   drivers/hwmon/Kconfig  |  11 ++
>   drivers/hwmon/Makefile |   1 +
>   drivers/hwmon/kb9002.c | 469 +++++++++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 489 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 9b4b1575bdbd..1d80ac2660e2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13931,6 +13931,14 @@ S:	Maintained
>   F:	Documentation/hwmon/k8temp.rst
>   F:	drivers/hwmon/k8temp.c
>   
> +KANDOU KB9002 PCIE RETIMER HWMON DRIVER
> +M:	Andy Chung <andy.chung@amd.com>
> +L:	linux-hwmon@vger.kernel.org
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/hwmon/kandou,kb9002.yaml
> +F:	Documentation/hwmon/kb9002.rst
> +F:	drivers/hwmon/kb9002.c
> +
>   KASAN
>   M:	Andrey Ryabinin <ryabinin.a.a@gmail.com>
>   R:	Alexander Potapenko <glider@google.com>
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 08c29685126a..300329773e87 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -335,6 +335,17 @@ config SENSORS_K10TEMP
>   	  This driver can also be built as a module. If so, the module
>   	  will be called k10temp.
>   
> +config SENSORS_KB9002
> +	tristate "Kandou KB9002 PCIe retimer"
> +	depends on I2C
> +	help
> +	  If you say yes here you get support for the integrated
> +	  temperature sensor and firmware version readout on Kandou
> +	  KB9002 PCIe 5.0 retimers, accessed over SMBus.
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called kb9002.
> +
>   config SENSORS_KBATT
>   	tristate "KEBA battery controller support"
>   	depends on KEBA_CP500
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 63809eeec2f4..0cad7e21634c 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -113,6 +113,7 @@ obj-$(CONFIG_SENSORS_IT87)	+= it87.o
>   obj-$(CONFIG_SENSORS_JC42)	+= jc42.o
>   obj-$(CONFIG_SENSORS_K8TEMP)	+= k8temp.o
>   obj-$(CONFIG_SENSORS_K10TEMP)	+= k10temp.o
> +obj-$(CONFIG_SENSORS_KB9002)	+= kb9002.o
>   obj-$(CONFIG_SENSORS_KBATT)	+= kbatt.o
>   obj-$(CONFIG_SENSORS_KFAN)	+= kfan.o
>   obj-$(CONFIG_SENSORS_LAN966X)	+= lan966x-hwmon.o
> diff --git a/drivers/hwmon/kb9002.c b/drivers/hwmon/kb9002.c
> new file mode 100644
> index 000000000000..61a6e522e770
> --- /dev/null
> +++ b/drivers/hwmon/kb9002.c
> @@ -0,0 +1,469 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Kandou KB9002 PCIe 5.0 retimer hwmon driver.
> + *
> + * The retimer exposes a system management bus (SMBus 3.0 with PEC)
> + * target for firmware-managed status registers. This driver assumes
> + * the chip is strapped to SMBus mode and exports the aggregated
> + * maximum die temperature as hwmon temp1_input (millidegrees Celsius)
> + * plus the firmware version and boot status under debugfs.
> + *
> + * Datasheet: Kandou KB9002 PCIe retimer (KA-015171-PD).
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/cleanup.h>
> +#include <linux/debugfs.h>
> +#include <linux/err.h>
> +#include <linux/hwmon.h>
> +#include <linux/i2c.h>
> +#include <linux/iopoll.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/seq_file.h>
> +#include <linux/types.h>
> +#include <linux/unaligned.h>
> +
> +#define KB9002_DEV_NAME			"kb9002"
> +
> +/*
> + * SMBus read command codes. Each read is a two-phase PEC-protected
> + * transaction: prime writes the target address, data reads it back with
> + * the register contents. FW reads use a 16-bit address, HW reads 32-bit.
> + */
> +#define KB9002_CC_FW_READ_PRIME		0x82
> +#define KB9002_CC_FW_READ_DATA		0x81
> +#define KB9002_CC_HW_READ_PRIME		0x8a
> +#define KB9002_CC_HW_READ_DATA		0x89
> +
> +/* Firmware register offsets (16-bit). */
> +#define KB9002_FW_REG_VID		0x0004
> +#define KB9002_FW_REG_FW_VERSION	0x0500
> +#define KB9002_FW_REG_TEMP_MAXIMUM	0x0550
> +
> +#define KB9002_VID_MASK			GENMASK(31, 16)
> +#define KB9002_VID_KANDOU		0x1e6f
> +
> +/* Firmware boot status: 0xe8 in the top byte means init completed OK. */
> +#define KB9002_HW_REG_FW_BOOT_STATUS	0xe0090008
> +#define KB9002_FW_BOOT_STATUS_OK_MSB	0xe8
> +
> +/*
> + * Hardware registers reached over raw I2C (32-bit addressing). The
> + * host-interface bit selects SMBus (set) vs raw-I2C target; parts
> + * strapped to raw I2C need it set before SMBus access works.
> + */
> +#define KB9002_HW_REG_REVID		0x00480004
> +#define KB9002_HW_REG_HOST_IF		0x00480008
> +#define KB9002_HOST_IF_SMBUS		BIT(1)
> +
> +#define KB9002_REVID_MASK		GENMASK(7, 0)
> +#define KB9002_REVID_B0			0x10
> +#define KB9002_REVID_B1			0x11
> +
> +/* Retries to drain a stray leading 0xff from the raw-I2C FIFO. */
> +#define KB9002_REVID_READ_RETRIES	16
> +
> +/* Temperature: 32-bit Q16.16 absolute Kelvin. */
> +#define KB9002_TEMP_FRAC_BITS		16
> +#define KB9002_ABS_ZERO_MILLI_C		(-273150)
> +
> +/* Firmware takes up to ~2s to respond after a host-interface change. */
> +#define KB9002_FW_READY_POLL_US		(25 * USEC_PER_MSEC)
> +#define KB9002_FW_READY_TIMEOUT_US	(2 * USEC_PER_SEC)
> +
> +struct kb9002_data {
> +	struct i2c_client *client;
> +	struct device *hwmon_dev;
> +};
> +
> +/* Raw-I2C read: write the 32-bit BE address, then read 4 BE data bytes. */
> +static int kb9002_i2c_read(struct i2c_client *client, u32 reg, u32 *val)
> +{
> +	u8 addr[4];
> +	u8 rbuf[4];
> +	struct i2c_msg msgs[2] = {
> +		{
> +			.addr = client->addr,
> +			.flags = 0,
> +			.len = sizeof(addr),
> +			.buf = addr,
> +		},
> +		{
> +			.addr = client->addr,
> +			.flags = I2C_M_RD,
> +			.len = sizeof(rbuf),
> +			.buf = rbuf,
> +		},
> +	};
> +	int ret;
> +
> +	put_unaligned_be32(reg, addr);
> +
> +	ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
> +	if (ret < 0)
> +		return ret;
> +	if (ret != ARRAY_SIZE(msgs))
> +		return -EIO;
> +
> +	*val = get_unaligned_be32(rbuf);
> +	return 0;
> +}
> +
> +/* Raw-I2C write: 4 BE address bytes followed by 4 BE data bytes. */
> +static int kb9002_i2c_write(struct i2c_client *client, u32 reg, u32 val)
> +{
> +	u8 buf[8];
> +	struct i2c_msg msg = {
> +		.addr = client->addr,
> +		.flags = 0,
> +		.len = sizeof(buf),
> +		.buf = buf,
> +	};
> +	int ret;
> +
> +	put_unaligned_be32(reg, &buf[0]);
> +	put_unaligned_be32(val, &buf[4]);
> +
> +	ret = i2c_transfer(client->adapter, &msg, 1);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +/*
> + * Read the silicon revision ID. A fresh FIFO may start with a stray
> + * 0xff that shifts the result, so drain one byte between retries until
> + * the top byte is no longer 0xff.
> + */
> +static int kb9002_read_revid(struct i2c_client *client, u32 *revid)
> +{
> +	u8 dummy;
> +	int ret;
> +	int i;
> +
> +	for (i = 0; i < KB9002_REVID_READ_RETRIES; i++) {
> +		ret = kb9002_i2c_read(client, KB9002_HW_REG_REVID, revid);
> +		if (ret)
> +			return ret;
> +		if ((*revid >> 24) != 0xff)
> +			return 0;
> +		/* Drain one byte from the chip to re-align the I2C FIFO. */
> +		i2c_master_recv(client, &dummy, 1);
> +	}
> +
> +	return -EIO;
> +}
> +
> +/*
> + * Read a 32-bit firmware register over SMBus: block-write the 16-bit LE
> + * address, then block-read the echoed address plus 4 LE data bytes.
> + */
> +static int kb9002_fw_read(struct kb9002_data *data, u16 reg, u32 *val)
> +{
> +	struct i2c_client *client = data->client;
> +	u8 addr[2];
> +	u8 rbuf[I2C_SMBUS_BLOCK_MAX];
> +	int ret;
> +
> +	put_unaligned_le16(reg, addr);
> +
> +	ret = i2c_smbus_write_block_data(client, KB9002_CC_FW_READ_PRIME,
> +					 sizeof(addr), addr);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = i2c_smbus_read_block_data(client, KB9002_CC_FW_READ_DATA, rbuf);
> +	if (ret < 0)
> +		return ret;
> +	if (ret < (int)(sizeof(addr) + sizeof(*val)))
> +		return -EIO;
> +
> +	*val = get_unaligned_le32(&rbuf[sizeof(addr)]);
> +	return 0;
> +}
> +
> +/* Like kb9002_fw_read but for a hardware register (32-bit LE address). */
> +static int kb9002_smbus_hw_read(struct kb9002_data *data, u32 reg, u32 *val)
> +{
> +	struct i2c_client *client = data->client;
> +	u8 addr[4];
> +	u8 rbuf[I2C_SMBUS_BLOCK_MAX];
> +	int ret;
> +
> +	put_unaligned_le32(reg, addr);
> +

Just for verification: Some accesses are LE, others are BE. This is unusual.
To help understand what is LE and what is BE, please add a comment at the
top o the file describing which accesses are LE and which accesses are BE.

> +	ret = i2c_smbus_write_block_data(client, KB9002_CC_HW_READ_PRIME,
> +					 sizeof(addr), addr);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = i2c_smbus_read_block_data(client, KB9002_CC_HW_READ_DATA, rbuf);
> +	if (ret < 0)
> +		return ret;
> +	if (ret < (int)(sizeof(addr) + sizeof(*val)))
> +		return -EIO;
> +
> +	*val = get_unaligned_le32(&rbuf[sizeof(addr)]);
> +	return 0;
> +}
> +
> +/*
> + * Switch the host interface from raw-I2C to SMBus and wait for firmware
> + * to come back up. Called only when SMBus access failed in probe, i.e.
> + * the chip is strapped to raw-I2C mode. Confirms the revision, sets the
> + * SMBus-mode bit, then polls until firmware responds again.
> + */
> +static int kb9002_enable_smbus_target(struct kb9002_data *data)
> +{
> +	struct i2c_client *client = data->client;
> +	u32 revid;
> +	u32 val;
> +	int op_ret;
> +	int ret;
> +
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> +		return dev_err_probe(&client->dev, -ENODEV,
> +				     "raw I2C required to switch to SMBus mode\n");
> +
> +	ret = kb9002_read_revid(client, &revid);
> +	if (ret)
> +		return dev_err_probe(&client->dev, ret,
> +				     "revision ID read failed\n");
> +
> +	switch (FIELD_GET(KB9002_REVID_MASK, revid)) {
> +	case KB9002_REVID_B0:
> +	case KB9002_REVID_B1:
> +		break;
> +	default:
> +		return dev_err_probe(&client->dev, -ENODEV,
> +				     "unsupported revision ID 0x%08x\n", revid);
> +	}
> +
> +	ret = kb9002_i2c_read(client, KB9002_HW_REG_HOST_IF, &val);
> +	if (ret)
> +		return dev_err_probe(&client->dev, ret,
> +				     "host interface read failed\n");
> +
> +	val |= KB9002_HOST_IF_SMBUS;
> +
> +	ret = kb9002_i2c_write(client, KB9002_HW_REG_HOST_IF, val);
> +	if (ret)
> +		return dev_err_probe(&client->dev, ret,
> +				     "host interface write failed\n");
> +
> +	/* Wait until firmware re-initialisation completes. */
> +	ret = read_poll_timeout(kb9002_fw_read, op_ret, op_ret == 0,
> +				KB9002_FW_READY_POLL_US,
> +				KB9002_FW_READY_TIMEOUT_US, true,
> +				data, KB9002_FW_REG_VID, &val);
> +	if (ret)
> +		return dev_err_probe(&client->dev, ret,
> +				     "firmware not responding over SMBus\n");
> +
> +	return 0;
> +}
> +
> +/* Convert Q16.16 absolute Kelvin to millidegrees Celsius. */
> +static long kb9002_temp_to_milli_c(u32 raw)
> +{
> +	s64 milli_k = ((s64)raw * 1000) >> KB9002_TEMP_FRAC_BITS;
> +
> +	return (long)milli_k + KB9002_ABS_ZERO_MILLI_C;
> +}
> +
> +static int kb9002_read_temp(struct kb9002_data *data, long *val)
> +{
> +	u32 raw;
> +	int ret;
> +
> +	ret = kb9002_fw_read(data, KB9002_FW_REG_TEMP_MAXIMUM, &raw);
> +	if (ret)
> +		return ret;
> +
> +	*val = kb9002_temp_to_milli_c(raw);
> +	return 0;
> +}
> +
> +static umode_t kb9002_is_visible(const void *drvdata,
> +				 enum hwmon_sensor_types type,
> +				 u32 attr, int channel)
> +{
> +	if (type == hwmon_temp &&
> +	    (attr == hwmon_temp_input || attr == hwmon_temp_label))
> +		return 0444;
> +	return 0;
> +}

In this context, the function can just return 0444 without any checks.

> +
> +static int kb9002_read(struct device *dev, enum hwmon_sensor_types type,
> +		       u32 attr, int channel, long *val)
> +{
> +	struct kb9002_data *data = dev_get_drvdata(dev);
> +
> +	if (type == hwmon_temp && attr == hwmon_temp_input)
> +		return kb9002_read_temp(data, val);
> +
> +	return -EOPNOTSUPP;
> +}
> +
> +static int kb9002_read_string(struct device *dev, enum hwmon_sensor_types type,
> +			      u32 attr, int channel, const char **str)
> +{
> +	if (type == hwmon_temp && attr == hwmon_temp_label) {
> +		*str = KB9002_DEV_NAME;
> +		return 0;
> +	}
> +	return -EOPNOTSUPP;
> +}

This is a pointless attribute. The label attribute is supposed to return
the sensor location, not the chip name. The chip name is already reported
in the "name" attribute. Please drop.

> +
> +static const struct hwmon_ops kb9002_hwmon_ops = {
> +	.is_visible = kb9002_is_visible,
> +	.read = kb9002_read,
> +	.read_string = kb9002_read_string,
> +};
> +
> +static const struct hwmon_channel_info * const kb9002_hwmon_info[] = {
> +	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT | HWMON_T_LABEL),
> +	NULL,
> +};
> +
> +static const struct hwmon_chip_info kb9002_chip_info = {
> +	.ops = &kb9002_hwmon_ops,
> +	.info = kb9002_hwmon_info,
> +};
> +
> +static int kb9002_fw_version_show(struct seq_file *s, void *unused)
> +{
> +	struct kb9002_data *data = s->private;
> +	u32 ver;
> +	int ret;
> +
> +	guard(hwmon_lock)(data->hwmon_dev);
> +
> +	ret = kb9002_fw_read(data, KB9002_FW_REG_FW_VERSION, &ver);
> +	if (ret)
> +		return ret;
> +
> +	seq_printf(s, "%u.%02u.%02u.%u\n",
> +		   (ver >> 24) & 0xff, (ver >> 16) & 0xff,
> +		   (ver >>  8) & 0xff, (ver >>  0) & 0xff);
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(kb9002_fw_version);
> +
> +static int kb9002_fw_load_status_show(struct seq_file *s, void *unused)
> +{
> +	struct kb9002_data *data = s->private;
> +	u32 status;
> +	int ret;
> +
> +	guard(hwmon_lock)(data->hwmon_dev);
> +
> +	ret = kb9002_smbus_hw_read(data, KB9002_HW_REG_FW_BOOT_STATUS, &status);
> +	if (ret)
> +		return ret;
> +
> +	seq_printf(s, "%s\n",
> +		   (status >> 24) == KB9002_FW_BOOT_STATUS_OK_MSB ?
> +		   "normal" : "abnormal");
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(kb9002_fw_load_status);
> +
> +static void kb9002_debugfs_init(struct kb9002_data *data)
> +{
> +	struct dentry *dir = data->client->debugfs;
> +
> +	debugfs_create_file("fw_ver", 0444, dir, data,
> +			    &kb9002_fw_version_fops);
> +	debugfs_create_file("fw_load_status", 0444, dir, data,
> +			    &kb9002_fw_load_status_fops);
> +}
> +
> +static int kb9002_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct kb9002_data *data;
> +	struct device *hwmon_dev;
> +	u32 vid;
> +	int ret;
> +
> +	if (!i2c_check_functionality(client->adapter,
> +				     I2C_FUNC_SMBUS_BLOCK_DATA |
> +				     I2C_FUNC_SMBUS_PEC))
> +		return -ENODEV;
> +
> +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->client = client;
> +
> +	/* All firmware register accesses are PEC-protected. */
> +	client->flags |= I2C_CLIENT_PEC;
> +

Doesn't this depend on controller PEC support (I2C_FUNC_SMBUS_PEC) ?
Also, the driver depends on I2C_FUNC_SMBUS_BLOCK_DATA support,
which is not always available. I would suggest to check for both.

Thanks,
Guenter

> +	i2c_set_clientdata(client, data);
> +
> +	/*
> +	 * Try SMBus first. If the chip is strapped to raw-I2C mode it
> +	 * will not respond to SMBus framing, so fall back to switching
> +	 * the host interface over raw I2C and retry.
> +	 */
> +	ret = kb9002_fw_read(data, KB9002_FW_REG_VID, &vid);
> +	if (ret) {
> +		dev_dbg(dev, "SMBus probe failed (%d), trying raw-I2C host-interface switch\n",
> +			ret);
> +		ret = kb9002_enable_smbus_target(data);
> +		if (ret)
> +			return ret;
> +		ret = kb9002_fw_read(data, KB9002_FW_REG_VID, &vid);
> +		if (ret)
> +			return dev_err_probe(dev, ret,
> +					     "VID read failed after host-interface switch\n");
> +	}
> +	if (FIELD_GET(KB9002_VID_MASK, vid) != KB9002_VID_KANDOU)
> +		return dev_err_probe(dev, -ENODEV,
> +				     "unexpected VID 0x%08x\n", vid);
> +
> +	hwmon_dev = devm_hwmon_device_register_with_info(dev, KB9002_DEV_NAME,
> +							 data,
> +							 &kb9002_chip_info,
> +							 NULL);
> +	if (IS_ERR(hwmon_dev))
> +		return PTR_ERR(hwmon_dev);
> +
> +	data->hwmon_dev = hwmon_dev;
> +	kb9002_debugfs_init(data);
> +	return 0;
> +}
> +
> +static const struct i2c_device_id kb9002_id[] = {
> +	{ .name = KB9002_DEV_NAME },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, kb9002_id);
> +
> +static const struct of_device_id kb9002_of_match[] = {
> +	{ .compatible = "kandou,kb9002" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, kb9002_of_match);
> +
> +static struct i2c_driver kb9002_driver = {
> +	.driver = {
> +		.name = KB9002_DEV_NAME,
> +		.of_match_table = kb9002_of_match,
> +	},
> +	.probe = kb9002_probe,
> +	.id_table = kb9002_id,
> +};
> +module_i2c_driver(kb9002_driver);
> +
> +MODULE_AUTHOR("Andy Chung <andy.chung@amd.com>");
> +MODULE_DESCRIPTION("Kandou KB9002 PCIe retimer hwmon driver");
> +MODULE_LICENSE("GPL");
> 

Re: [PATCH v3 3/4] hwmon: (kb9002) Add driver for Kandou KB9002 retimer

[Andy Chung]

On Tue, 21 Jul 2026 07:43:11 -0700, Guenter Roeck wrote:
> Doesn't this depend on controller PEC support (I2C_FUNC_SMBUS_PEC) ?
> Also, the driver depends on I2C_FUNC_SMBUS_BLOCK_DATA support,
> which is not always available. I would suggest to check for both.

probe() already requires both before setting I2C_CLIENT_PEC:

	if (!i2c_check_functionality(client->adapter,
				     I2C_FUNC_SMBUS_BLOCK_DATA |
				     I2C_FUNC_SMBUS_PEC))
		return -ENODEV;

so the flag is only set on adapters that support PEC. The endianness,
is_visible and temp1_label comments are addressed in v5.

Thanks,
Andy

[PATCH v3 4/4] hwmon: (kb9002) Add documentation

[Andy Chung via B4 Relay]

From: Andy Chung <Andy.Chung@amd.com>

Document the sysfs and debugfs interfaces of the Kandou KB9002 hwmon
driver.

Signed-off-by: Andy Chung <Andy.Chung@amd.com>
---
 Documentation/hwmon/index.rst  |  1 +
 Documentation/hwmon/kb9002.rst | 65 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 226789376217..9dc796d087dc 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -112,6 +112,7 @@ Hardware Monitoring Kernel Drivers
    jc42
    k10temp
    k8temp
+   kb9002
    kbatt
    kfan
    lan966x
diff --git a/Documentation/hwmon/kb9002.rst b/Documentation/hwmon/kb9002.rst
new file mode 100644
index 000000000000..e6d8d9c78923
--- /dev/null
+++ b/Documentation/hwmon/kb9002.rst
@@ -0,0 +1,65 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver kb9002
+====================
+
+Supported chips:
+
+  * Kandou KB9002
+
+    Prefix: 'kb9002'
+
+    Addresses scanned: -
+
+    Datasheet: KA-015171-PD (available from Kandou under NDA)
+
+Author: Andy Chung <andy.chung@amd.com>
+
+Description
+-----------
+
+The Kandou KB9002 is an 8-lane PCIe 5.0 retimer with an integrated
+microcontroller. It exposes an SMBus 3.0 target (with mandatory PEC)
+on its sideband interface. The internal firmware aggregates per-lane
+die temperatures and publishes the maximum value through a 16-bit
+addressed register window.
+
+This driver reports that aggregated maximum as the only hwmon
+temperature channel. The running firmware version and the firmware
+boot status are exposed under debugfs.
+
+sysfs interface
+---------------
+
+==================  ===============================================
+temp1_input         Aggregated maximum die temperature across all
+                    active lanes (millidegrees Celsius).
+temp1_label         Always "kb9002".
+==================  ===============================================
+
+debugfs interface
+-----------------
+
+Files live in the per-client debugfs directory created by the I2C
+core: ``/sys/kernel/debug/i2c/i2c-<bus>/<bus>-<addr>/``.
+
+==================  ===============================================
+fw_ver              Running firmware version in
+                    "major.minor.patch.suffix" format. Read-only.
+fw_load_status      Firmware boot status: "normal" once firmware has
+                    finished initialising, "abnormal" otherwise.
+                    Read-only.
+==================  ===============================================
+
+Notes
+-----
+
+The driver requires ``I2C_FUNC_SMBUS_BLOCK_DATA``,
+``I2C_FUNC_SMBUS_PEC`` and ``I2C_FUNC_I2C`` from the host adapter. The
+last is needed only during probe for the host-interface mode switch;
+runtime accesses use SMBus block transactions exclusively.
+
+The retimer's SMBus address is configurable on three strap pins and
+ranges from 0x20 to 0x27. The address is selected through device tree
+(or i2c board info) the same way as any other I2C device; the driver
+does not auto-detect.

-- 
2.34.1