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Message-ID: <20221228164934.GB1267483@roeck-us.net>
Date: Wed, 28 Dec 2022 08:49:34 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: "Cormier, Jonathan" <jcormier@...ticallink.com>
Cc: linux-hwmon@...r.kernel.org,
John Pruitt <jpruitt@...ticallink.com>,
Jean Delvare <jdelvare@...e.com>, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Bob Duke <bduke@...ticallink.com>
Subject: Re: [PATCH v2 3/4] hwmon: ltc2945: Allow setting shunt resistor
On Mon, Dec 19, 2022 at 07:04:56PM -0500, Cormier, Jonathan wrote:
> From: John Pruitt <jpruitt@...ticallink.com>
>
> Added the ability to specify the value of the shunt resistor in the
a/Added/Add/
Per Documentation/process/submitting-patches.rst:
"
Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
to do frotz", as if you are giving orders to the codebase to change
its behaviour.
"
> device tree instead of assuming it is 1 milliOhm. The value in the
> device tree has the name shunt-resistor-micro-ohms and the
> default value is 1000 micro-ohms in order to preserve the
> current behavior.
>
> Signed-off-by: "Cormier, Jonathan" <jcormier@...ticallink.com>
> Signed-off-by: John Pruitt <jpruitt@...ticallink.com>
> ---
> drivers/hwmon/ltc2945.c | 80 +++++++++++++++++++++++++----------------
> 1 file changed, 50 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c
> index 9af3e3821152..fc7d399b2c85 100644
> --- a/drivers/hwmon/ltc2945.c
> +++ b/drivers/hwmon/ltc2945.c
> @@ -64,6 +64,16 @@ static const struct of_device_id __maybe_unused ltc2945_of_match[] = {
> };
> MODULE_DEVICE_TABLE(of, ltc2945_of_match);
>
> +/**
> + * struct ltc2945_data - LTC2945 device data
> + * @regmap: regmap device
> + * @shunt_resistor: shunt resistor value in micro ohms (1000 by default)
> + */
> +struct ltc2945_data {
> + struct regmap *regmap;
> + u32 shunt_resistor;
> +};
> +
> static inline bool is_power_reg(u8 reg)
> {
> return reg < LTC2945_SENSE_H;
> @@ -72,7 +82,9 @@ static inline bool is_power_reg(u8 reg)
> /* Return the value from the given register in uW, mV, or mA */
> static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
> {
> - struct regmap *regmap = dev_get_drvdata(dev);
> + struct ltc2945_data *data = dev_get_drvdata(dev);
> + struct regmap *regmap = data->regmap;
> + u32 shunt_resistor = data->shunt_resistor;
> unsigned int control;
> u8 buf[3];
> long long val;
> @@ -98,9 +110,7 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
> case LTC2945_MAX_POWER_THRES_H:
> case LTC2945_MIN_POWER_THRES_H:
> /*
> - * Convert to uW by assuming current is measured with
> - * an 1mOhm sense resistor, similar to current
> - * measurements.
> + * Convert to uW
> * Control register bit 0 selects if voltage at SENSE+/VDD
> * or voltage at ADIN is used to measure power.
> */
> @@ -114,6 +124,8 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
> /* 0.5 mV * 25 uV = 0.0125 uV resolution. */
> val = (val * 25LL) >> 1;
> }
> + val *= 1000;
> + val = DIV_ROUND_CLOSEST_ULL(val, shunt_resistor);
> break;
> case LTC2945_VIN_H:
> case LTC2945_MAX_VIN_H:
> @@ -136,14 +148,9 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
> case LTC2945_MIN_SENSE_H:
> case LTC2945_MAX_SENSE_THRES_H:
> case LTC2945_MIN_SENSE_THRES_H:
> - /*
> - * 25 uV resolution. Convert to current as measured with
> - * an 1 mOhm sense resistor, in mA. If a different sense
> - * resistor is installed, calculate the actual current by
> - * dividing the reported current by the sense resistor value
> - * in mOhm.
> - */
> - val *= 25;
> + /* 25 uV resolution. Convert to mA. */
> + val *= 25 * 1000;
> + val = DIV_ROUND_CLOSEST_ULL(val, shunt_resistor);
> break;
> default:
> return -EINVAL;
> @@ -154,7 +161,9 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
> static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> unsigned long val)
> {
> - struct regmap *regmap = dev_get_drvdata(dev);
> + struct ltc2945_data *data = dev_get_drvdata(dev);
> + struct regmap *regmap = data->regmap;
> + u32 shunt_resistor = data->shunt_resistor;
> unsigned int control;
> int ret;
>
> @@ -165,9 +174,6 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> case LTC2945_MAX_POWER_THRES_H:
> case LTC2945_MIN_POWER_THRES_H:
> /*
> - * Convert to register value by assuming current is measured
> - * with an 1mOhm sense resistor, similar to current
> - * measurements.
> * Control register bit 0 selects if voltage at SENSE+/VDD
> * or voltage at ADIN is used to measure power, which in turn
> * determines register calculations.
> @@ -177,14 +183,16 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> return ret;
> if (control & CONTROL_MULT_SELECT) {
> /* 25 mV * 25 uV = 0.625 uV resolution. */
> - val = DIV_ROUND_CLOSEST(val, 625);
> + val *= shunt_resistor;
> + val = DIV_ROUND_CLOSEST(val, 625 * 1000);
Overflows are introduced and need to be be handled in this patch.
It doesn't make sense to introduce them and fix them in the next patch.
> } else {
> /*
> * 0.5 mV * 25 uV = 0.0125 uV resolution.
> * Divide first to avoid overflow;
> * accept loss of accuracy.
> */
> - val = DIV_ROUND_CLOSEST(val, 25) * 2;
> + val *= shunt_resistor;
> + val = DIV_ROUND_CLOSEST(val, 25 * 1000) * 2;
> }
> break;
> case LTC2945_VIN_H:
> @@ -208,14 +216,9 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> case LTC2945_MIN_SENSE_H:
> case LTC2945_MAX_SENSE_THRES_H:
> case LTC2945_MIN_SENSE_THRES_H:
> - /*
> - * 25 uV resolution. Convert to current as measured with
> - * an 1 mOhm sense resistor, in mA. If a different sense
> - * resistor is installed, calculate the actual current by
> - * dividing the reported current by the sense resistor value
> - * in mOhm.
> - */
> - val = DIV_ROUND_CLOSEST(val, 25);
> + /* 25 uV resolution. Convert to mA. */
> + val *= shunt_resistor;
> + val = DIV_ROUND_CLOSEST(val, 25 * 1000);
> break;
> default:
> return -EINVAL;
> @@ -240,7 +243,8 @@ static ssize_t ltc2945_value_store(struct device *dev,
> const char *buf, size_t count)
> {
> struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
> - struct regmap *regmap = dev_get_drvdata(dev);
> + struct ltc2945_data *data = dev_get_drvdata(dev);
> + struct regmap *regmap = data->regmap;
> u8 reg = attr->index;
> unsigned long val;
> u8 regbuf[3];
> @@ -275,7 +279,8 @@ static ssize_t ltc2945_history_store(struct device *dev,
> const char *buf, size_t count)
> {
> struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
> - struct regmap *regmap = dev_get_drvdata(dev);
> + struct ltc2945_data *data = dev_get_drvdata(dev);
> + struct regmap *regmap = data->regmap;
> u8 reg = attr->index;
> int num_regs = is_power_reg(reg) ? 3 : 2;
> u8 buf_min[3] = { 0xff, 0xff, 0xff };
> @@ -327,7 +332,8 @@ static ssize_t ltc2945_bool_show(struct device *dev,
> struct device_attribute *da, char *buf)
> {
> struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
> - struct regmap *regmap = dev_get_drvdata(dev);
> + struct ltc2945_data *data = dev_get_drvdata(dev);
> + struct regmap *regmap = data->regmap;
> unsigned int fault;
> int ret;
>
> @@ -456,6 +462,12 @@ static int ltc2945_probe(struct i2c_client *client)
> struct device *dev = &client->dev;
> struct device *hwmon_dev;
> struct regmap *regmap;
> + struct ltc2945_data *data;
> +
> + data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> + dev_set_drvdata(dev, data);
>
> regmap = devm_regmap_init_i2c(client, <c2945_regmap_config);
> if (IS_ERR(regmap)) {
> @@ -463,11 +475,19 @@ static int ltc2945_probe(struct i2c_client *client)
> return PTR_ERR(regmap);
> }
>
> + data->regmap = regmap;
> + if (device_property_read_u32(dev, "shunt-resistor-micro-ohms",
> + &data->shunt_resistor))
> + data->shunt_resistor = 1000;
> +
> + if (data->shunt_resistor == 0)
> + return -EINVAL;
> +
> /* Clear faults */
> regmap_write(regmap, LTC2945_FAULT, 0x00);
>
> hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
> - regmap,
> + data,
> ltc2945_groups);
> return PTR_ERR_OR_ZERO(hwmon_dev);
> }
> --
> 2.25.1
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