[PATCH v5 0/2] dt-bindings: hwmon: pmbus: add bindings for isl68137

[PATCH v5 0/2] dt-bindings: hwmon: pmbus: add bindings for isl68137

[Grant Peltier]

Renesas digital multiphase voltage regulators are capable of regulating
output voltages that exceed the range that their Vsense pins can detect.
In such applications, users may place a voltage divider between Vout and
the Vsense pin for a given rail. However, the driver currently has no
way of knowing if a voltage divider is being used which results in
erroneous telemetry being reported over hwmon.

This patch set defines a devicetree bindings schema for Renesas digital
multiphase voltage regulators that are supported by the isl68137 driver
to allow users to add voltage divider definitions for any rail powered
by the device. This patch set also includes the required changes to the
isl68137 driver to enable scaling Vout/Pout telemetry for rails with a
defined voltage divider.

v5:
- Fix clang compilation errors related to C23 syntax

v4:
- Revert devicetree property name to "vout-voltage-divider" and refactor
  property description and driver implementation to match existing
  vout-voltage-divider implementation in max20730 as no suitable generic
  voltage divider schema exists.
- Minor fixes based on Guenter's review of v2.
- Initialize voltage dividers for all channels to defaults that simplify
  logic in PMBus word read/write functions.

v3:
- Report and return errors reading the vout-voltage-divider property from
  the devicetree when the property is defined
- Change u64 division/rounding operations to use explicit math64 macros

v2:
- Fix devicetree bindings schema errors
- Add "renesas," vendor prefix to "vout-voltage-divider" property
- Rebase patch series on v6.12-rc1

Grant Peltier (2):
  hwmon: (pmbus/isl68137) add support for voltage divider on Vout
  dt-bindings: hwmon: isl68137: add bindings to support voltage dividers

 .../hwmon/pmbus/renesas,isl68137.yaml         | 147 ++++++++++++
 drivers/hwmon/pmbus/isl68137.c                | 209 +++++++++++++++++-
 2 files changed, 351 insertions(+), 5 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/hwmon/pmbus/renesas,isl68137.yaml

-- 
2.39.5

[PATCH v5 1/2] hwmon: (pmbus/isl68137) add support for voltage divider on Vout

[Grant Peltier]

Some applications require Vout to be higher than the detectable voltage
range of the Vsense pin for a given rail. In such applications, a voltage
divider may be placed between Vout and the Vsense pin, but this results
in erroneous telemetry being read back from the part. This change adds
support for a voltage divider to be defined in the devicetree for a (or
multiple) specific rail(s) for a supported digital multiphase device and
for the applicable Vout telemetry to be scaled based on the voltage
divider configuration.

Signed-off-by: Grant Peltier <grantpeltier93@gmail.com>
---
 drivers/hwmon/pmbus/isl68137.c | 209 ++++++++++++++++++++++++++++++++-
 1 file changed, 204 insertions(+), 5 deletions(-)

diff --git a/drivers/hwmon/pmbus/isl68137.c b/drivers/hwmon/pmbus/isl68137.c
index 7e53fb1d5ea3..cd0cc82c18e7 100644
--- a/drivers/hwmon/pmbus/isl68137.c
+++ b/drivers/hwmon/pmbus/isl68137.c
@@ -13,6 +13,7 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/of.h>
 #include <linux/string.h>
 #include <linux/sysfs.h>
 
@@ -20,6 +21,7 @@
 
 #define ISL68137_VOUT_AVS	0x30
 #define RAA_DMPVR2_READ_VMON	0xc8
+#define MAX_CHANNELS            4
 
 enum chips {
 	isl68137,
@@ -72,6 +74,17 @@ enum variants {
 	raa_dmpvr2_hv,
 };
 
+struct isl68137_channel {
+	u32 vout_voltage_divider[2];
+};
+
+struct isl68137_data {
+	struct pmbus_driver_info info;
+	struct isl68137_channel channel[MAX_CHANNELS];
+};
+
+#define to_isl68137_data(x)	container_of(x, struct isl68137_data, info)
+
 static const struct i2c_device_id raa_dmpvr_id[];
 
 static ssize_t isl68137_avs_enable_show_page(struct i2c_client *client,
@@ -163,13 +176,32 @@ static const struct attribute_group *isl68137_attribute_groups[] = {
 static int raa_dmpvr2_read_word_data(struct i2c_client *client, int page,
 				     int phase, int reg)
 {
+	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
+	const struct isl68137_data *data = to_isl68137_data(info);
 	int ret;
+	u64 temp;
 
 	switch (reg) {
 	case PMBUS_VIRT_READ_VMON:
 		ret = pmbus_read_word_data(client, page, phase,
 					   RAA_DMPVR2_READ_VMON);
 		break;
+	case PMBUS_READ_POUT:
+	case PMBUS_READ_VOUT:
+		/*
+		 * In cases where a voltage divider is attached to the target
+		 * rail between Vout and the Vsense pin, both Vout and Pout
+		 * should be scaled by the voltage divider scaling factor.
+		 * I.e. Vout = Vsense * Rtotal / Rout
+		 */
+		ret = pmbus_read_word_data(client, page, phase, reg);
+		if (ret > 0) {
+			temp = DIV_U64_ROUND_CLOSEST((u64)ret *
+				data->channel[page].vout_voltage_divider[1],
+				data->channel[page].vout_voltage_divider[0]);
+			ret = clamp_val(temp, 0, 0xffff);
+		}
+		break;
 	default:
 		ret = -ENODATA;
 		break;
@@ -178,6 +210,40 @@ static int raa_dmpvr2_read_word_data(struct i2c_client *client, int page,
 	return ret;
 }
 
+static int raa_dmpvr2_write_word_data(struct i2c_client *client, int page,
+				      int reg, u16 word)
+{
+	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
+	const struct isl68137_data *data = to_isl68137_data(info);
+	int ret;
+	u64 temp;
+
+	switch (reg) {
+	case PMBUS_VOUT_MAX:
+	case PMBUS_VOUT_MARGIN_HIGH:
+	case PMBUS_VOUT_MARGIN_LOW:
+	case PMBUS_VOUT_OV_FAULT_LIMIT:
+	case PMBUS_VOUT_UV_FAULT_LIMIT:
+	case PMBUS_VOUT_COMMAND:
+		/*
+		 * In cases where a voltage divider is attached to the target
+		 * rail between Vout and the Vsense pin, Vout related PMBus
+		 * commands should be scaled based on the expected voltage
+		 * at the Vsense pin.
+		 * I.e. Vsense = Vout * Rout / Rtotal
+		 */
+		temp = DIV_U64_ROUND_CLOSEST((u64)word *
+				data->channel[page].vout_voltage_divider[0],
+				data->channel[page].vout_voltage_divider[1]);
+		ret = clamp_val(temp, 0, 0xffff);
+		break;
+	default:
+		ret = -ENODATA;
+		break;
+	}
+	return ret;
+}
+
 static struct pmbus_driver_info raa_dmpvr_info = {
 	.pages = 3,
 	.format[PSC_VOLTAGE_IN] = direct,
@@ -220,14 +286,91 @@ static struct pmbus_driver_info raa_dmpvr_info = {
 	    | PMBUS_HAVE_STATUS_IOUT | PMBUS_HAVE_POUT,
 };
 
+static int isl68137_probe_child_from_dt(struct device *dev,
+					struct device_node *child,
+					struct isl68137_data *data)
+{
+	u32 channel, rout, rtotal;
+	int err;
+
+	err = of_property_read_u32(child, "reg", &channel);
+	if (err) {
+		dev_err(dev, "missing reg property of %pOFn\n", child);
+		return err;
+	}
+	if (channel >= data->info.pages) {
+		dev_err(dev, "invalid reg %d of %pOFn\n", channel, child);
+		return -EINVAL;
+	}
+
+	err = of_property_read_u32_array(child, "vout-voltage-divider",
+				data->channel[channel].vout_voltage_divider,
+				ARRAY_SIZE(data->channel[channel].vout_voltage_divider));
+	if (err && err != -EINVAL) {
+		dev_err(dev,
+			"malformed vout-voltage-divider value for channel %d\n",
+			channel);
+		return err;
+	}
+
+	rout = data->channel[channel].vout_voltage_divider[0];
+	rtotal = data->channel[channel].vout_voltage_divider[1];
+	if (rout == 0) {
+		dev_err(dev,
+			"Voltage divider output resistance must be greater than 0\n");
+		return -EINVAL;
+	}
+	if (rtotal < rout) {
+		dev_err(dev,
+			"Voltage divider total resistance is less than output resistance\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int isl68137_probe_from_dt(struct device *dev,
+				  struct isl68137_data *data)
+{
+	const struct device_node *np = dev->of_node;
+	struct device_node *child;
+	int err;
+
+	for_each_child_of_node(np, child) {
+		if (strcmp(child->name, "channel"))
+			continue;
+
+		err = isl68137_probe_child_from_dt(dev, child, data);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 static int isl68137_probe(struct i2c_client *client)
 {
+	struct device *dev = &client->dev;
 	struct pmbus_driver_info *info;
+	struct isl68137_data *data;
+	int i, err;
 
-	info = devm_kzalloc(&client->dev, sizeof(*info), GFP_KERNEL);
-	if (!info)
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
 		return -ENOMEM;
-	memcpy(info, &raa_dmpvr_info, sizeof(*info));
+
+	/*
+	 * Initialize all voltage dividers to Rout=1 and Rtotal=1 to simplify
+	 * logic in PMBus word read/write functions
+	 */
+	for (i = 0; i < MAX_CHANNELS; i++)
+		memset(data->channel[i].vout_voltage_divider,
+			1,
+			sizeof(data->channel[i].vout_voltage_divider));
+
+
+	memcpy(&data->info, &raa_dmpvr_info, sizeof(data->info));
+	info = &data->info;
 
 	switch (i2c_match_id(raa_dmpvr_id, client)->driver_data) {
 	case raa_dmpvr1_2rail:
@@ -242,6 +385,7 @@ static int isl68137_probe(struct i2c_client *client)
 	case raa_dmpvr2_1rail:
 		info->pages = 1;
 		info->read_word_data = raa_dmpvr2_read_word_data;
+		info->write_word_data = raa_dmpvr2_write_word_data;
 		break;
 	case raa_dmpvr2_2rail_nontc:
 		info->func[0] &= ~PMBUS_HAVE_TEMP3;
@@ -250,9 +394,11 @@ static int isl68137_probe(struct i2c_client *client)
 	case raa_dmpvr2_2rail:
 		info->pages = 2;
 		info->read_word_data = raa_dmpvr2_read_word_data;
+		info->write_word_data = raa_dmpvr2_write_word_data;
 		break;
 	case raa_dmpvr2_3rail:
 		info->read_word_data = raa_dmpvr2_read_word_data;
+		info->write_word_data = raa_dmpvr2_write_word_data;
 		break;
 	case raa_dmpvr2_hv:
 		info->pages = 1;
@@ -263,11 +409,16 @@ static int isl68137_probe(struct i2c_client *client)
 		info->m[PSC_POWER] = 2;
 		info->R[PSC_POWER] = -1;
 		info->read_word_data = raa_dmpvr2_read_word_data;
+		info->write_word_data = raa_dmpvr2_write_word_data;
 		break;
 	default:
 		return -ENODEV;
 	}
 
+	err = isl68137_probe_from_dt(dev, data);
+	if (err)
+		return err;
+
 	return pmbus_do_probe(client, info);
 }
 
@@ -318,11 +469,59 @@ static const struct i2c_device_id raa_dmpvr_id[] = {
 
 MODULE_DEVICE_TABLE(i2c, raa_dmpvr_id);
 
+static const struct of_device_id isl68137_of_match[] = {
+	{ .compatible = "renesas,isl68137", .data = (void *)raa_dmpvr1_2rail },
+	{ .compatible = "renesas,isl68220", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl68221", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl68222", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl68223", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl68224", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl68225", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl68226", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl68227", .data = (void *)raa_dmpvr2_1rail },
+	{ .compatible = "renesas,isl68229", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl68233", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl68239", .data = (void *)raa_dmpvr2_3rail },
+
+	{ .compatible = "renesas,isl69222", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69223", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl69224", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69225", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69227", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl69228", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl69234", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69236", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69239", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl69242", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69243", .data = (void *)raa_dmpvr2_1rail },
+	{ .compatible = "renesas,isl69247", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69248", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69254", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69255", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69256", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69259", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69260", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69268", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,isl69269", .data = (void *)raa_dmpvr2_3rail },
+	{ .compatible = "renesas,isl69298", .data = (void *)raa_dmpvr2_2rail },
+
+	{ .compatible = "renesas,raa228000", .data = (void *)raa_dmpvr2_hv },
+	{ .compatible = "renesas,raa228004", .data = (void *)raa_dmpvr2_hv },
+	{ .compatible = "renesas,raa228006", .data = (void *)raa_dmpvr2_hv },
+	{ .compatible = "renesas,raa228228", .data = (void *)raa_dmpvr2_2rail_nontc },
+	{ .compatible = "renesas,raa229001", .data = (void *)raa_dmpvr2_2rail },
+	{ .compatible = "renesas,raa229004", .data = (void *)raa_dmpvr2_2rail },
+	{ },
+};
+
+MODULE_DEVICE_TABLE(of, isl68137_of_match);
+
 /* This is the driver that will be inserted */
 static struct i2c_driver isl68137_driver = {
 	.driver = {
-		   .name = "isl68137",
-		   },
+		.name = "isl68137",
+		.of_match_table = isl68137_of_match,
+	},
 	.probe = isl68137_probe,
 	.id_table = raa_dmpvr_id,
 };
-- 
2.39.5

[PATCH v5 2/2] dt-bindings: hwmon: isl68137: add bindings to support voltage dividers

[Grant Peltier]

Add devicetree bindings to support declaring optional voltage dividers to
the rail outputs of supported digital multiphase regulators. Some
applications require Vout to exceed the voltage range that the Vsense pin
can detect. This binding definition allows users to define the
characteristics of a voltage divider placed between Vout and the Vsense
pin for any rail powered by the device.

Signed-off-by: Grant Peltier <grantpeltier93@gmail.com>
---
 .../hwmon/pmbus/renesas,isl68137.yaml         | 147 ++++++++++++++++++
 1 file changed, 147 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/pmbus/renesas,isl68137.yaml

diff --git a/Documentation/devicetree/bindings/hwmon/pmbus/renesas,isl68137.yaml b/Documentation/devicetree/bindings/hwmon/pmbus/renesas,isl68137.yaml
new file mode 100644
index 000000000000..ed659c2baadf
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/pmbus/renesas,isl68137.yaml
@@ -0,0 +1,147 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+
+$id: http://devicetree.org/schemas/hwmon/pmbus/renesas,isl68137.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Renesas Digital Multiphase Voltage Regulators with PMBus
+
+maintainers:
+  - Grant Peltier <grant.peltier.jg@renesas.com>
+
+description: |
+  Renesas digital multiphase voltage regulators with PMBus.
+  https://www.renesas.com/en/products/power-management/multiphase-power/multiphase-dcdc-switching-controllers
+
+properties:
+  compatible:
+    enum:
+      - renesas,isl68220
+      - renesas,isl68221
+      - renesas,isl68222
+      - renesas,isl68223
+      - renesas,isl68224
+      - renesas,isl68225
+      - renesas,isl68226
+      - renesas,isl68227
+      - renesas,isl68229
+      - renesas,isl68233
+      - renesas,isl68239
+      - renesas,isl69222
+      - renesas,isl69223
+      - renesas,isl69224
+      - renesas,isl69225
+      - renesas,isl69227
+      - renesas,isl69228
+      - renesas,isl69234
+      - renesas,isl69236
+      - renesas,isl69239
+      - renesas,isl69242
+      - renesas,isl69243
+      - renesas,isl69247
+      - renesas,isl69248
+      - renesas,isl69254
+      - renesas,isl69255
+      - renesas,isl69256
+      - renesas,isl69259
+      - renesas,isl69260
+      - renesas,isl69268
+      - renesas,isl69269
+      - renesas,isl69298
+      - renesas,raa228000
+      - renesas,raa228004
+      - renesas,raa228006
+      - renesas,raa228228
+      - renesas,raa229001
+      - renesas,raa229004
+
+  reg:
+    maxItems: 1
+
+  '#address-cells':
+    const: 1
+
+  '#size-cells':
+    const: 0
+
+patternProperties:
+  "^channel@([0-3])$":
+    type: object
+    description:
+      Container for properties specific to a particular channel (rail).
+
+    properties:
+      reg:
+        description: The channel (rail) index.
+        items:
+          minimum: 0
+          maximum: 3
+
+      vout-voltage-divider:
+        description: |
+          Resistances of a voltage divider placed between Vout and the voltage
+          sense (Vsense) pin for the given channel (rail). It has two numbers
+          representing the resistances of the voltage divider provided as
+          <Rout Rtotal> which yields an adjusted Vout as
+          Vout_adj = Vout * Rtotal / Rout given the original Vout as reported
+          by the Vsense pin. Given a circuit configuration similar to the one
+          below, Rtotal = R1 + Rout.
+
+            Vout ----.
+                     |
+                  .-----.
+                  | R1  |
+                  '-----'
+                     |
+                     +---- Vsense
+                     |
+                  .-----.
+                  | Rout|
+                  '-----'
+                     |
+                    GND
+
+        $ref: /schemas/types.yaml#/definitions/uint32-array
+        minItems: 2
+        maxItems: 2
+
+    required:
+      - reg
+
+    additionalProperties: false
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      isl68239@60 {
+        compatible = "renesas,isl68239";
+        reg = <0x60>;
+      };
+    };
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      isl68239@60 {
+        compatible = "renesas,isl68239";
+        reg = <0x60>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        channel@0 {
+          reg = <0>;
+          vout-voltage-divider = <1000 2000>;  // Reported Vout/Pout would be scaled by 2
+        };
+      };
+    };
-- 
2.39.5

Re: [PATCH v5 2/2] dt-bindings: hwmon: isl68137: add bindings to support voltage dividers

[Rob Herring (Arm)]

On Fri, 25 Oct 2024 12:17:28 -0500, Grant Peltier wrote:
> Add devicetree bindings to support declaring optional voltage dividers to
> the rail outputs of supported digital multiphase regulators. Some
> applications require Vout to exceed the voltage range that the Vsense pin
> can detect. This binding definition allows users to define the
> characteristics of a voltage divider placed between Vout and the Vsense
> pin for any rail powered by the device.
> 
> Signed-off-by: Grant Peltier <grantpeltier93@gmail.com>
> ---
>  .../hwmon/pmbus/renesas,isl68137.yaml         | 147 ++++++++++++++++++
>  1 file changed, 147 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/pmbus/renesas,isl68137.yaml
> 

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>

Re: [PATCH v5 0/2] dt-bindings: hwmon: pmbus: add bindings for isl68137

[Geert Uytterhoeven]

Hi Grant,

On Fri, Oct 25, 2024 at 7:16 PM Grant Peltier <grantpeltier93@gmail.com> wrote:
> Renesas digital multiphase voltage regulators are capable of regulating
> output voltages that exceed the range that their Vsense pins can detect.
> In such applications, users may place a voltage divider between Vout and
> the Vsense pin for a given rail. However, the driver currently has no
> way of knowing if a voltage divider is being used which results in
> erroneous telemetry being reported over hwmon.
>
> This patch set defines a devicetree bindings schema for Renesas digital
> multiphase voltage regulators that are supported by the isl68137 driver
> to allow users to add voltage divider definitions for any rail powered
> by the device. This patch set also includes the required changes to the
> isl68137 driver to enable scaling Vout/Pout telemetry for rails with a
> defined voltage divider.
>
> v5:
> - Fix clang compilation errors related to C23 syntax

Thanks for the update!

> v4:
> - Revert devicetree property name to "vout-voltage-divider" and refactor
>   property description and driver implementation to match existing
>   vout-voltage-divider implementation in max20730 as no suitable generic
>   voltage divider schema exists.

Can you please elaborate (or point to the email that did so, in case
I missed it)?

In reply to v2, Günter wrote:

   "I would prefer, in the order of preference,

    1) an applicable generic property definition
    2) a definition that is already used elsewhere
    3) a new chips specific definition"

https://lore.kernel.org/all/3f460b62-4cd1-49dd-a98b-1fbcfdbd3af0@roeck-us.net

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v5 0/2] dt-bindings: hwmon: pmbus: add bindings for isl68137

[Grant Peltier]

On Mon, Oct 28, 2024 at 11:18:39AM +0100, Geert Uytterhoeven wrote:
> > v4:
> > - Revert devicetree property name to "vout-voltage-divider" and refactor
> >   property description and driver implementation to match existing
> >   vout-voltage-divider implementation in max20730 as no suitable generic
> >   voltage divider schema exists.
> 
> Can you please elaborate (or point to the email that did so, in case
> I missed it)?
> 
> In reply to v2, Günter wrote:
> 
>    "I would prefer, in the order of preference,
> 
>     1) an applicable generic property definition
>     2) a definition that is already used elsewhere
>     3) a new chips specific definition"
> 
> https://lore.kernel.org/all/3f460b62-4cd1-49dd-a98b-1fbcfdbd3af0@roeck-us.net
> 
> Thanks!
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
>

Hi Geert,

After looking through existing bindings definitions, the only generic
voltage divider property that I found was one that is intended to scale
voltages for IIO io-channels. However, the use case here is to scale
particular hwmon PMBus telemetry, which most closely matches the existing
implementation of the vout-voltage-divider property in the max20730
driver so I opted to copy that implementation based on Guenter's
preferences. Is there something that I missed or more information that
you are looking for?

Thanks,
Grant

Re: [PATCH v5 0/2] dt-bindings: hwmon: pmbus: add bindings for isl68137

[Guenter Roeck]

On 10/29/24 09:32, Grant Peltier wrote:
> On Mon, Oct 28, 2024 at 11:18:39AM +0100, Geert Uytterhoeven wrote:
>>> v4:
>>> - Revert devicetree property name to "vout-voltage-divider" and refactor
>>>    property description and driver implementation to match existing
>>>    vout-voltage-divider implementation in max20730 as no suitable generic
>>>    voltage divider schema exists.
>>
>> Can you please elaborate (or point to the email that did so, in case
>> I missed it)?
>>
>> In reply to v2, Günter wrote:
>>
>>     "I would prefer, in the order of preference,
>>
>>      1) an applicable generic property definition
>>      2) a definition that is already used elsewhere
>>      3) a new chips specific definition"
>>
>> https://lore.kernel.org/all/3f460b62-4cd1-49dd-a98b-1fbcfdbd3af0@roeck-us.net
>>
>> Thanks!
>>
>> Gr{oetje,eeting}s,
>>
>>                          Geert
>>
> 
> Hi Geert,
> 
> After looking through existing bindings definitions, the only generic
> voltage divider property that I found was one that is intended to scale
> voltages for IIO io-channels. However, the use case here is to scale
> particular hwmon PMBus telemetry, which most closely matches the existing
> implementation of the vout-voltage-divider property in the max20730
> driver so I opted to copy that implementation based on Guenter's
> preferences. Is there something that I missed or more information that
> you are looking for?
> 

I had a look myself. I agree with Grant, the existing bindings are really
not a good match. They are directly tied to iio, the implementation in
drivers/iio/afe/iio-rescale.c is completely iio specific, and I see
no means to use it for anything but iio. The problem is that it is
a "compatible" property, not parameter property (or set of properties)
as I would have expected [sorry if I use the wrong terminology].

We could possibly use the actual properties, "output-ohms" and "full-ohms",
but I am not really sure if that makes too much sense.

Note that there are a variety of voltage divider properties.

gw,voltage-divider-ohms
lltc,fb-voltage-divider
mps,fb-voltage-divider
vout-voltage-divider

All those specify a pair of resistors. I think that model is much better
suited to the problem at hand than a "compatible".

I agree though that this should be explained in the patch description.

Guenter