drivers/hwmon/ina238.c | 45 ++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 42 insertions(+), 3 deletions(-)
The INA238 sensor reports shunt voltage with microvolt precision.
However, the hwmon driver currently exposes this value only in
millivolts via `in0_input`, which results in a loss of precision for
readings within the range of ±1 mV.
This patch introduces an `in0_scale` attribute to provide the scaling
factor applied to the shunt voltage reading. By exposing this attribute,
users can accurately interpret the in0_input values in microvolts,
preserving the sensor's full precision.
Signed-off-by: Potin Lai <potin.lai.pt@gmail.com>
---
drivers/hwmon/ina238.c | 45 ++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 42 insertions(+), 3 deletions(-)
diff --git a/drivers/hwmon/ina238.c b/drivers/hwmon/ina238.c
index 2d9f12f68d50..58737a0703dc 100644
--- a/drivers/hwmon/ina238.c
+++ b/drivers/hwmon/ina238.c
@@ -8,6 +8,7 @@
#include <linux/err.h>
#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
@@ -108,8 +109,42 @@ struct ina238_data {
struct regmap *regmap;
u32 rshunt;
int gain;
+ long shunt_volt_scale;
};
+static ssize_t shunt_volt_scale_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct ina238_data *data = dev_get_drvdata(dev);
+
+ return sprintf(buf, "%d\n", data->shunt_volt_scale);
+}
+
+static ssize_t shunt_volt_scale_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct ina238_data *data = dev_get_drvdata(dev);
+ long val;
+ int err;
+
+ err = kstrtol(buf, 10, &val);
+ if (err)
+ return err;
+
+ data->shunt_volt_scale = val;
+ return count;
+}
+
+static SENSOR_DEVICE_ATTR_RW(in0_scale, shunt_volt_scale, 0);
+
+static struct attribute *ina238_attrs[] = {
+ &sensor_dev_attr_in0_scale.dev_attr.attr,
+ NULL,
+};
+
+ATTRIBUTE_GROUPS(ina238);
+
static int ina238_read_reg24(const struct i2c_client *client, u8 reg, u32 *val)
{
u8 data[3];
@@ -197,8 +232,9 @@ static int ina238_read_in(struct device *dev, u32 attr, int channel,
regval = (s16)regval;
if (channel == 0)
/* gain of 1 -> LSB / 4 */
- *val = (regval * INA238_SHUNT_VOLTAGE_LSB) /
- (1000 * (4 - data->gain + 1));
+ *val = (regval * INA238_SHUNT_VOLTAGE_LSB *
+ data->shunt_volt_scale) /
+ (1000 * (4 - data->gain + 1));
else
*val = (regval * INA238_BUS_VOLTAGE_LSB) / 1000;
break;
@@ -603,9 +639,12 @@ static int ina238_probe(struct i2c_client *client)
return -ENODEV;
}
+ /* Setup default shunt voltage scale */
+ data->shunt_volt_scale = 1;
+
hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name, data,
&ina238_chip_info,
- NULL);
+ ina238_groups);
if (IS_ERR(hwmon_dev))
return PTR_ERR(hwmon_dev);
---
base-commit: fc033cf25e612e840e545f8d5ad2edd6ba613ed5
change-id: 20250121-potin-ina238-shunt-voltage-scaling-8a3f9dc3d2b8
Best regards,
--
Potin Lai <potin.lai.pt@gmail.com>
Hi Potin,
kernel test robot noticed the following build warnings:
[auto build test WARNING on fc033cf25e612e840e545f8d5ad2edd6ba613ed5]
url: https://github.com/intel-lab-lkp/linux/commits/Potin-Lai/hwmon-ina238-Add-support-for-shunt-voltage-scaling/20250121-002826
base: fc033cf25e612e840e545f8d5ad2edd6ba613ed5
patch link: https://lore.kernel.org/r/20250121-potin-ina238-shunt-voltage-scaling-v1-1-36d5dfe027f5%40gmail.com
patch subject: [PATCH] hwmon: ina238: Add support for shunt voltage scaling
config: x86_64-buildonly-randconfig-004-20250121 (https://download.01.org/0day-ci/archive/20250121/202501211015.8Szwv3Cd-lkp@intel.com/config)
compiler: clang version 19.1.3 (https://github.com/llvm/llvm-project ab51eccf88f5321e7c60591c5546b254b6afab99)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250121/202501211015.8Szwv3Cd-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202501211015.8Szwv3Cd-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> drivers/hwmon/ina238.c:120:30: warning: format specifies type 'int' but the argument has type 'long' [-Wformat]
120 | return sprintf(buf, "%d\n", data->shunt_volt_scale);
| ~~ ^~~~~~~~~~~~~~~~~~~~~~
| %ld
1 warning generated.
vim +120 drivers/hwmon/ina238.c
114
115 static ssize_t shunt_volt_scale_show(struct device *dev,
116 struct device_attribute *attr, char *buf)
117 {
118 struct ina238_data *data = dev_get_drvdata(dev);
119
> 120 return sprintf(buf, "%d\n", data->shunt_volt_scale);
121 }
122
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Hi Potin,
kernel test robot noticed the following build warnings:
[auto build test WARNING on fc033cf25e612e840e545f8d5ad2edd6ba613ed5]
url: https://github.com/intel-lab-lkp/linux/commits/Potin-Lai/hwmon-ina238-Add-support-for-shunt-voltage-scaling/20250121-002826
base: fc033cf25e612e840e545f8d5ad2edd6ba613ed5
patch link: https://lore.kernel.org/r/20250121-potin-ina238-shunt-voltage-scaling-v1-1-36d5dfe027f5%40gmail.com
patch subject: [PATCH] hwmon: ina238: Add support for shunt voltage scaling
config: i386-buildonly-randconfig-004-20250121 (https://download.01.org/0day-ci/archive/20250121/202501210454.YUnMEUaA-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250121/202501210454.YUnMEUaA-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202501210454.YUnMEUaA-lkp@intel.com/
All warnings (new ones prefixed by >>):
drivers/hwmon/ina238.c: In function 'shunt_volt_scale_show':
>> drivers/hwmon/ina238.c:120:31: warning: format '%d' expects argument of type 'int', but argument 3 has type 'long int' [-Wformat=]
120 | return sprintf(buf, "%d\n", data->shunt_volt_scale);
| ~^ ~~~~~~~~~~~~~~~~~~~~~~
| | |
| int long int
| %ld
vim +120 drivers/hwmon/ina238.c
114
115 static ssize_t shunt_volt_scale_show(struct device *dev,
116 struct device_attribute *attr, char *buf)
117 {
118 struct ina238_data *data = dev_get_drvdata(dev);
119
> 120 return sprintf(buf, "%d\n", data->shunt_volt_scale);
121 }
122
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On 1/20/25 08:23, Potin Lai wrote: > The INA238 sensor reports shunt voltage with microvolt precision. > However, the hwmon driver currently exposes this value only in > millivolts via `in0_input`, which results in a loss of precision for > readings within the range of ±1 mV. > > This patch introduces an `in0_scale` attribute to provide the scaling > factor applied to the shunt voltage reading. By exposing this attribute, > users can accurately interpret the in0_input values in microvolts, > preserving the sensor's full precision. > > Signed-off-by: Potin Lai <potin.lai.pt@gmail.com> Sorry, this is an ABI violation and thus a no-go. in0_input is and will always be reported in mV. Guenter
On Tue, Jan 21, 2025 at 12:38 AM Guenter Roeck <linux@roeck-us.net> wrote: > > On 1/20/25 08:23, Potin Lai wrote: > > The INA238 sensor reports shunt voltage with microvolt precision. > > However, the hwmon driver currently exposes this value only in > > millivolts via `in0_input`, which results in a loss of precision for > > readings within the range of ±1 mV. > > > > This patch introduces an `in0_scale` attribute to provide the scaling > > factor applied to the shunt voltage reading. By exposing this attribute, > > users can accurately interpret the in0_input values in microvolts, > > preserving the sensor's full precision. > > > > Signed-off-by: Potin Lai <potin.lai.pt@gmail.com> > > Sorry, this is an ABI violation and thus a no-go. in0_input is and will > always be reported in mV. > > Guenter > Hi Guenter, In our use case, the shunt voltage is less than 1 mv most of the time. I would like to get your advice on the correct way of getting microvolt reading from the driver? Thank you. Best regards, Potin
On 1/20/25 17:18, Potin Lai wrote:
> On Tue, Jan 21, 2025 at 12:38 AM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> On 1/20/25 08:23, Potin Lai wrote:
>>> The INA238 sensor reports shunt voltage with microvolt precision.
>>> However, the hwmon driver currently exposes this value only in
>>> millivolts via `in0_input`, which results in a loss of precision for
>>> readings within the range of ±1 mV.
>>>
>>> This patch introduces an `in0_scale` attribute to provide the scaling
>>> factor applied to the shunt voltage reading. By exposing this attribute,
>>> users can accurately interpret the in0_input values in microvolts,
>>> preserving the sensor's full precision.
>>>
>>> Signed-off-by: Potin Lai <potin.lai.pt@gmail.com>
>>
>> Sorry, this is an ABI violation and thus a no-go. in0_input is and will
>> always be reported in mV.
>>
>> Guenter
>>
>
> Hi Guenter,
> In our use case, the shunt voltage is less than 1 mv most of the time.
> I would like to get your advice on the correct way of getting
> microvolt reading from the driver? Thank you.
>
Given that V = I * R, assuming you know the shunt resistor value,
it is an easy calculation which does not require any code changes.
Possible alternatives:
- Create a debugfs file to display the voltage in uV.
See drivers/hwmon/isl28022.c for an example.
- Implement a hwmon -> iio bridge and use IIO to report
the voltage.
Having said that, do you have an actual use case ? What is the point
of knowing the voltage across the shunt resistor ? "Because the chip
reports it" is not a use case. Literally _every_ current sensor chip
ultimately reports the shunt resistor voltage, after all (typically
as current; calculation see above). Commit 63fb21afc1f5 ("hwmon:
(ina2xx) Use shunt voltage to calculate current") is a case in point.
Guenter
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