[PATCH 1/2] hwmon: (sht4x) Fix EREMOTEIO errors

[PATCH 1/2] hwmon: (sht4x) Fix EREMOTEIO errors

[David Mosberger-Tang]

Per datasheet, SHT4x may need up to 8.2ms for a "high repeatability"
measurement to complete.  Attempting to read the result too early
triggers a NAK which then causes an EREMOTEIO error.

This behavior has been confirmed with a logic analyzer while running
the I2C bus at only 40kHz.  The low frequency precludes any
signal-integrity issues, which was also confirmed by the absence of
any CRC8 errors.  In this configuration, a NAK occurred on any read
that followed the measurement command within less than 8.2ms.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
---
 drivers/hwmon/sht4x.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
index 09c2a0b06444..3415d7a0e0fc 100644
--- a/drivers/hwmon/sht4x.c
+++ b/drivers/hwmon/sht4x.c
@@ -23,7 +23,7 @@
 /*
  * I2C command delays (in microseconds)
  */
-#define SHT4X_MEAS_DELAY	1000
+#define SHT4X_MEAS_DELAY_HPM	8200	/* see t_MEAS,h in datasheet */
 #define SHT4X_DELAY_EXTRA	10000
 
 /*
@@ -90,7 +90,7 @@ static int sht4x_read_values(struct sht4x_data *data)
 	if (ret < 0)
 		goto unlock;
 
-	usleep_range(SHT4X_MEAS_DELAY, SHT4X_MEAS_DELAY + SHT4X_DELAY_EXTRA);
+	usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
 
 	ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
 	if (ret != SHT4X_RESPONSE_LENGTH) {
-- 
2.25.1

[PATCH 2/2] hwmon: (sht4x) Add device tree match table and document it

[David Mosberger-Tang]

This patch enables automatic loading of the sht4x module via a device
tree table entry.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
---
 .../bindings/hwmon/sensirion,sht4x.yaml       | 50 +++++++++++++++++++
 arch/arm/boot/dts/egauge-cpk.dts              |  5 ++
 drivers/hwmon/sht4x.c                         |  7 +++
 3 files changed, 62 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/sensirion,sht4x.yaml

diff --git a/Documentation/devicetree/bindings/hwmon/sensirion,sht4x.yaml b/Documentation/devicetree/bindings/hwmon/sensirion,sht4x.yaml
new file mode 100644
index 000000000000..588c2e37b035
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/sensirion,sht4x.yaml
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/hwmon/sensirion,sht4x.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sensirion SHT4x Humidity and Temperature Sensor IC
+
+maintainers:
+  - Navin Sankar Velliangiri navin@linumiz.com
+
+description: |
+  The SHT4x is a high-accuracy digital humidity and temperature sensor
+  designed especially for battery-driven high-volume consumer
+  electronics applications.  For further information refere to
+  Documentation/hwmon/sht4x.rst
+
+  This binding document describes the binding for the hardware monitor
+  portion of the driver.
+
+properties:
+  compatible:
+    enum:
+      - sensirion,sht4x
+
+  reg:
+    const: 0x44
+    description:
+      The I2c base address of the SHT4x.  0x44 for all chip versions
+      except for SHT41-BD1B, where it is 0x45.
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      clock-frequency = <400000>;
+
+      sht4x@44 {
+        compatible = "sensirion,sht4x";
+        reg = <0x44>;
+      };
+    };
+...
diff --git a/arch/arm/boot/dts/egauge-cpk.dts b/arch/arm/boot/dts/egauge-cpk.dts
index 17f85b2d54a2..ee8b52c92248 100644
--- a/arch/arm/boot/dts/egauge-cpk.dts
+++ b/arch/arm/boot/dts/egauge-cpk.dts
@@ -477,6 +477,11 @@ tmp102@48 {
 					reg = <0x48>;
 					pagesize = <16>;
 				};
+
+				sht4x@44 {
+					compatible = "sensirion,sht4x";
+					reg = <0x44>;
+				};
 			};
 
 			securam: sram@f8044000 {
diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
index 3415d7a0e0fc..6e53d81e32d4 100644
--- a/drivers/hwmon/sht4x.c
+++ b/drivers/hwmon/sht4x.c
@@ -281,9 +281,16 @@ static const struct i2c_device_id sht4x_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, sht4x_id);
 
+static const struct of_device_id sht4x_of_match[] = {
+	{ .compatible = "sensirion,sht4x" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, sht4x_of_match);
+
 static struct i2c_driver sht4x_driver = {
 	.driver = {
 		.name = "sht4x",
+		.of_match_table = sht4x_of_match
 	},
 	.probe		= sht4x_probe,
 	.id_table	= sht4x_id,
-- 
2.25.1