[RFC PATCH 1/2] platform: arm64: qcom-hamoa-ec: monitor Slim 7x legacy sensors

[Birk Skyum]

The Yoga Slim 7x EC returns an all-zero response to the reference-board
thermal capability command. Probe fails even though its legacy RPM and
thermistor queries work and firmware controls the fan automatically.

Select a read-only path for the Lenovo compatible. Expose its first RPM
channel and thermistor through hwmon, validating the transfer length and
RPM payload count and treating the thermistor's 0xff sentinel as ENODATA.
Do not enable SCI, register manual cooling controls or send standby
commands on this path. Keep the reference-board behavior and strict
capability validation unchanged.

The transactions are documented by the Yoga's FC22 and FC29/TZ39 DSDT
methods and Maya Matuszczyk's EC protocol notes. Anvesh Jain P's pending
fan-profile series also documents the RPM query. This change does not
include its calibration, LUT programming or temperature reporting.

Link: https://github.com/aarch64-laptops/build/blob/2e58842f5fa2f87771c2df017ae4d8c65225ef10/misc/lenovo-yoga-slim-7x/acpi/dsdt.dsl
Link: https://lkml.iu.edu/hypermail/linux/kernel/2607.3/08806.html
Signed-off-by: Birk Skyum <birk.skyum@xxxxx>
---
 Documentation/hwmon/index.rst          |   1 +
 Documentation/hwmon/qcom-ec.rst        |  40 +++++++
 MAINTAINERS                            |   1 +
 drivers/platform/arm64/Kconfig         |   4 +-
 drivers/platform/arm64/qcom-hamoa-ec.c | 153 ++++++++++++++++++++++++-
 5 files changed, 194 insertions(+), 5 deletions(-)
 create mode 100644 Documentation/hwmon/qcom-ec.rst

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 9955a5254..7ce23ea5a 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -233,6 +233,7 @@ Hardware Monitoring Kernel Drivers
    pxe1610
    pwm-fan
    q54sj108a2
+   qcom-ec
    qnap-mcu-hwmon
    raspberrypi-hwmon
    sbrmi
diff --git a/Documentation/hwmon/qcom-ec.rst b/Documentation/hwmon/qcom-ec.rst
new file mode 100644
index 000000000..11f9f2347
--- /dev/null
+++ b/Documentation/hwmon/qcom-ec.rst
@@ -0,0 +1,40 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+Kernel driver qcom-hamoa-ec
+==========================
+
+Supported systems:
+
+  * Lenovo Yoga Slim 7x (14Q8X9)
+
+    Prefix: 'qcom_ec'
+
+    I2C address: 0x76, instantiated from the device tree. No scanning.
+
+Description
+-----------
+
+The Yoga Slim 7x embedded controller provides a fan speed channel and a
+thermistor through a legacy interface. It does not provide the thermal
+capability response used by the Qualcomm reference-board interface.
+
+On this system the driver only reads sensors. Cooling remains under firmware
+control, including when the driver is unloaded. The driver does not change
+fan curves, fan profiles, PWM settings, SCI events or EC standby state.
+The exposed RPM channel does not establish the number of physical fans.
+
+The hwmon interface is selected by the ``lenovo,yoga-slim7x-ec`` compatible.
+It is not exposed on Qualcomm reference boards by this driver.
+
+Sysfs attributes
+----------------
+
+All attributes below are read-only.
+
+=============== ======================================================
+fan1_input      Fan speed in RPM. Zero is valid when the fan is stopped.
+temp1_input     EC thermistor temperature in millidegrees Celsius.
+=============== ======================================================
+
+An unavailable thermistor reading returns ``ENODATA``. A malformed fan
+response or an incomplete bus transfer returns an error, not a zero speed.
diff --git a/MAINTAINERS b/MAINTAINERS
index 6215fcb07..8518a97b4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -22441,6 +22441,7 @@ M:	Sibi Sankar <sibi.sankar@xxxxxxxxxxxxxxxx>
 L:	linux-arm-msm@xxxxxxxxxxxxxxx
 S:	Maintained
 F:	Documentation/devicetree/bindings/embedded-controller/qcom,hamoa-crd-ec.yaml
+F:	Documentation/hwmon/qcom-ec.rst
 F:	drivers/platform/arm64/qcom-hamoa-ec.c
 
 QUALCOMM HEXAGON ARCHITECTURE
diff --git a/drivers/platform/arm64/Kconfig b/drivers/platform/arm64/Kconfig
index e32e01b2a..4f338c715 100644
--- a/drivers/platform/arm64/Kconfig
+++ b/drivers/platform/arm64/Kconfig
@@ -94,6 +94,7 @@ config EC_QCOM_HAMOA
 	tristate "Embedded Controller driver for Qualcomm Hamoa/Glymur reference devices"
 	depends on ARCH_QCOM || COMPILE_TEST
 	depends on I2C
+	depends on HWMON
 	depends on THERMAL || THERMAL=n
 	help
 	  Say M or Y here to enable the Embedded Controller driver for Qualcomm
@@ -101,6 +102,7 @@ config EC_QCOM_HAMOA
 	  control, temperature sensors, access to EC state changes and supports
 	  reporting suspend entry/exit to the EC.
 
-	  This driver currently supports Hamoa/Purwa/Glymur reference devices.
+	  This driver supports Hamoa/Purwa/Glymur reference devices and read-only
+	  fan speed and temperature monitoring on the Lenovo Yoga Slim 7x.
 
 endif # ARM64_PLATFORM_DEVICES
diff --git a/drivers/platform/arm64/qcom-hamoa-ec.c b/drivers/platform/arm64/qcom-hamoa-ec.c
index 4d2ad042a..3a4ca8a0d 100644
--- a/drivers/platform/arm64/qcom-hamoa-ec.c
+++ b/drivers/platform/arm64/qcom-hamoa-ec.c
@@ -9,6 +9,7 @@
 #include <linux/device.h>
 #include <linux/dev_printk.h>
 #include <linux/err.h>
+#include <linux/hwmon.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
@@ -16,10 +17,13 @@
 #include <linux/pm.h>
 #include <linux/slab.h>
 #include <linux/thermal.h>
+#include <linux/unaligned.h>
 
 #define EC_SCI_EVT_READ_CMD	0x05
 #define EC_FW_VERSION_CMD	0x0e
+#define EC_FAN_RPM_QUERY_CMD	0x22
 #define EC_MODERN_STANDBY_CMD	0x23
+#define EC_THERMISTOR1_CMD	0x29
 #define EC_FAN_DBG_CONTROL_CMD	0x30
 #define EC_SCI_EVT_CONTROL_CMD	0x35
 #define EC_THERMAL_CAP_CMD	0x42
@@ -76,13 +80,126 @@ struct qcom_ec_cooling_dev {
 	u8 state;
 };
 
+struct qcom_ec_variant {
+	bool monitor_only;
+};
+
 struct qcom_ec {
+	const struct qcom_ec_variant *variant;
 	struct qcom_ec_cooling_dev *ec_cdev;
 	struct qcom_ec_thermal_cap thermal_cap;
 	struct qcom_ec_version version;
 	struct i2c_client *client;
 };
 
+/* FC22 in the Slim 7x DSDT: command, fan ID; count, little-endian RPM. */
+static int qcom_ec_read_fan_rpm(struct qcom_ec *ec, long *val)
+{
+	struct i2c_client *client = ec->client;
+	u8 request[] = { EC_FAN_RPM_QUERY_CMD, 1 };
+	u8 response[3];
+	struct i2c_msg messages[] = {
+		{
+			.addr = client->addr,
+			.len = sizeof(request),
+			.buf = request,
+		}, {
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.len = sizeof(response),
+			.buf = response,
+		},
+	};
+	int ret;
+
+	ret = i2c_transfer(client->adapter, messages, ARRAY_SIZE(messages));
+	if (ret < 0)
+		return ret;
+	if (ret != ARRAY_SIZE(messages))
+		return -EIO;
+	if (response[0] != sizeof(response) - 1)
+		return -EPROTO;
+
+	*val = get_unaligned_le16(&response[1]);
+
+	return 0;
+}
+
+static umode_t qcom_ec_hwmon_is_visible(const void *data, enum hwmon_sensor_types type,
+					u32 attr, int channel)
+{
+	if (channel)
+		return 0;
+	if ((type == hwmon_fan && attr == hwmon_fan_input) ||
+	    (type == hwmon_temp && attr == hwmon_temp_input))
+		return 0444;
+
+	return 0;
+}
+
+static int qcom_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
+			      u32 attr, int channel, long *val)
+{
+	struct qcom_ec *ec = dev_get_drvdata(dev);
+	int ret;
+
+	if (channel)
+		return -EOPNOTSUPP;
+
+	if (type == hwmon_fan && attr == hwmon_fan_input)
+		return qcom_ec_read_fan_rpm(ec, val);
+
+	if (type != hwmon_temp || attr != hwmon_temp_input)
+		return -EOPNOTSUPP;
+
+	/* FC29/TZ39 report degrees Celsius, or 0xff if unavailable. */
+	ret = i2c_smbus_read_byte_data(ec->client, EC_THERMISTOR1_CMD);
+	if (ret < 0)
+		return ret;
+	if (ret == 0xff)
+		return -ENODATA;
+
+	*val = ret * 1000;
+
+	return 0;
+}
+
+static const struct hwmon_ops qcom_ec_hwmon_ops = {
+	.is_visible = qcom_ec_hwmon_is_visible,
+	.read = qcom_ec_hwmon_read,
+};
+
+static const struct hwmon_channel_info * const qcom_ec_hwmon_info[] = {
+	HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT),
+	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
+	NULL,
+};
+
+static const struct hwmon_chip_info qcom_ec_hwmon_chip_info = {
+	.ops = &qcom_ec_hwmon_ops,
+	.info = qcom_ec_hwmon_info,
+};
+
+static int qcom_ec_hwmon_probe(struct qcom_ec *ec)
+{
+	struct device *dev = &ec->client->dev;
+	struct device *hwmon;
+	long rpm;
+	int ret;
+
+	if (!i2c_check_functionality(ec->client->adapter,
+				     I2C_FUNC_I2C | I2C_FUNC_SMBUS_READ_BYTE_DATA))
+		return -EOPNOTSUPP;
+
+	ret = qcom_ec_read_fan_rpm(ec, &rpm);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to read fan RPM\n");
+
+	hwmon = devm_hwmon_device_register_with_info(dev, "qcom_ec", ec,
+						     &qcom_ec_hwmon_chip_info, NULL);
+	return PTR_ERR_OR_ZERO(hwmon);
+}
+
 static int qcom_ec_read(struct qcom_ec *ec, u8 cmd, u8 resp_len, u8 *resp)
 {
 	int ret;
@@ -331,6 +448,10 @@ static const struct thermal_cooling_device_ops qcom_ec_thermal_ops = {
 static int qcom_ec_resume(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct qcom_ec *ec = i2c_get_clientdata(client);
+
+	if (ec->variant->monitor_only)
+		return 0;
 
 	return i2c_smbus_write_byte_data(client, EC_MODERN_STANDBY_CMD,
 					 EC_MODERN_STANDBY_EXIT);
@@ -339,6 +460,10 @@ static int qcom_ec_resume(struct device *dev)
 static int qcom_ec_suspend(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct qcom_ec *ec = i2c_get_clientdata(client);
+
+	if (ec->variant->monitor_only)
+		return 0;
 
 	return i2c_smbus_write_byte_data(client, EC_MODERN_STANDBY_CMD,
 					 EC_MODERN_STANDBY_ENTER);
@@ -356,14 +481,24 @@ static int qcom_ec_probe(struct i2c_client *client)
 		return -ENOMEM;
 
 	ec->client = client;
+	ec->variant = i2c_get_match_data(client);
+	if (!ec->variant)
+		return -ENODEV;
+	i2c_set_clientdata(client, ec);
+
+	/*
+	 * The Slim 7x does not implement the reference-board capability command.
+	 * Its firmware controls cooling autonomously. Only expose its legacy
+	 * sensors; do not enable SCI, fan debug control or standby notifications.
+	 */
+	if (ec->variant->monitor_only)
+		return qcom_ec_hwmon_probe(ec);
 
 	ret = devm_request_threaded_irq(dev, client->irq, NULL, qcom_ec_irq,
 					IRQF_ONESHOT, "qcom_ec", ec);
 	if (ret < 0)
 		return ret;
 
-	i2c_set_clientdata(client, ec);
-
 	ret = qcom_ec_read_fw_version(dev);
 	if (ret < 0)
 		return dev_err_probe(dev, ret, "Failed to read EC firmware version\n");
@@ -410,6 +545,9 @@ static void qcom_ec_remove(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	int ret;
 
+	if (ec->variant->monitor_only)
+		return;
+
 	ret = qcom_ec_sci_evt_control(dev, false);
 	if (ret < 0)
 		dev_err(dev, "Failed to disable SCI events: %d\n", ret);
@@ -421,14 +559,21 @@ static void qcom_ec_remove(struct i2c_client *client)
 	}
 }
 
+static const struct qcom_ec_variant qcom_ec_reference = {};
+
+static const struct qcom_ec_variant qcom_ec_slim7x = {
+	.monitor_only = true,
+};
+
 static const struct of_device_id qcom_ec_of_match[] = {
-	{ .compatible = "qcom,hamoa-crd-ec" },
+	{ .compatible = "lenovo,yoga-slim7x-ec", .data = &qcom_ec_slim7x },
+	{ .compatible = "qcom,hamoa-crd-ec", .data = &qcom_ec_reference },
 	{}
 };
 MODULE_DEVICE_TABLE(of, qcom_ec_of_match);
 
 static const struct i2c_device_id qcom_ec_i2c_id_table[] = {
-	{ "qcom-hamoa-ec", },
+	{ "qcom-hamoa-ec", (kernel_ulong_t)&qcom_ec_reference },
 	{}
 };
 MODULE_DEVICE_TABLE(i2c, qcom_ec_i2c_id_table);
-- 
2.53.0