Date:   Tue, 26 Sep 2023 12:36:18 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Naresh Solanki <naresh.solanki@...ements.com>
Cc:     broonie@...nel.org, zev@...ilderbeest.net,
        Liam Girdwood <lgirdwood@...il.com>,
        Jean Delvare <jdelvare@...e.com>, linux-kernel@...r.kernel.org,
        linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v4] regulator (max5970): Add hwmon support

On Tue, Sep 19, 2023 at 07:48:23AM +0200, Naresh Solanki wrote:
> Utilize the integrated 10-bit ADC in Max5970/Max5978 to enable voltage
> and current monitoring. This feature is seamlessly integrated through
> the hwmon subsystem.
> 
> Signed-off-by: Naresh Solanki <naresh.solanki@...ements.com>
> ---
> Changes in V4:
> - Use IS_REACHABLE
> - Use rdevs array for hwmon ops.
> - Remove duplicate i2c_set_clientdata
> Changes in V3:
> - Update signed-off
> - Add break
> - Update hwmon dev register name to max5970
> - Remove changes in Kconfig.
> Changes in V2:
> - default case added for switch statement
> - Add dependency on HWMON
> ---
>  drivers/regulator/max5970-regulator.c | 138 +++++++++++++++++++++++++-
>  1 file changed, 136 insertions(+), 2 deletions(-)
> 
> 
> base-commit: 41f02a383ac652f1a0b5538c5901b7ec93e37290
> 
> diff --git a/drivers/regulator/max5970-regulator.c b/drivers/regulator/max5970-regulator.c
> index b56a174cde3d..06168fe1dadd 100644
> --- a/drivers/regulator/max5970-regulator.c
> +++ b/drivers/regulator/max5970-regulator.c
> @@ -10,6 +10,7 @@
>  #include <linux/bitops.h>
>  #include <linux/device.h>
>  #include <linux/err.h>
> +#include <linux/hwmon.h>
>  #include <linux/module.h>
>  #include <linux/io.h>
>  #include <linux/of.h>
> @@ -32,6 +33,128 @@ enum max597x_regulator_id {
>  	MAX597X_SW1,
>  };
>  
> +static int max5970_read_adc(struct regmap *regmap, int reg, long *val)
> +{
> +	u8 reg_data[2];
> +	int ret;
> +
> +	ret = regmap_bulk_read(regmap, reg, &reg_data[0], 2);
> +	if (ret < 0)
> +		return ret;
> +
> +	*val = (reg_data[0] << 2) | (reg_data[1] & 3);
> +
> +	return 0;
> +}
> +
> +static int max5970_read(struct device *dev, enum hwmon_sensor_types type,
> +			u32 attr, int channel, long *val)
> +{
> +	struct regulator_dev **rdevs = dev_get_drvdata(dev);
> +	struct max5970_regulator *ddata = rdev_get_drvdata(rdevs[channel]);
> +	struct regmap *regmap = ddata->regmap;
> +	int ret;
> +
> +	switch (type) {
> +	case hwmon_curr:
> +		switch (attr) {
> +		case hwmon_curr_input:
> +			ret = max5970_read_adc(regmap, MAX5970_REG_CURRENT_H(channel), val);
> +			/*
> +			 * Calculate current from ADC value, IRNG range & shunt resistor value.
> +			 * ddata->irng holds the voltage corresponding to the maximum value the
> +			 * 10-bit ADC can measure.
> +			 * To obtain the output, multiply the ADC value by the IRNG range (in
> +			 * millivolts) and then divide it by the maximum value of the 10-bit ADC.
> +			 */
> +			*val = (*val * ddata->irng) >> 10;
> +			/* Convert the voltage meansurement across shunt resistor to current */
> +			*val = (*val * 1000) / ddata->shunt_micro_ohms;
> +			return ret;
> +		default:
> +			return -EOPNOTSUPP;
> +		}
> +
> +	case hwmon_in:
> +		switch (attr) {
> +		case hwmon_in_input:
> +			ret = max5970_read_adc(regmap, MAX5970_REG_VOLTAGE_H(channel), val);
> +			/*
> +			 * Calculate voltage from ADC value and MON range.
> +			 * ddata->mon_rng holds the voltage corresponding to the maximum value the
> +			 * 10-bit ADC can measure.
> +			 * To obtain the output, multiply the ADC value by the MON range (in
> +			 * microvolts) and then divide it by the maximum value of the 10-bit ADC.
> +			 */
> +			*val = mul_u64_u32_shr(*val, ddata->mon_rng, 10);
> +			/* uV to mV */
> +			*val = *val / 1000;
> +			return ret;
> +		default:
> +			return -EOPNOTSUPP;
> +		}
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +}
> +
> +static umode_t max5970_is_visible(const void *data,
> +				  enum hwmon_sensor_types type,
> +				  u32 attr, int channel)
> +{
> +	struct regulator_dev **rdevs = (struct regulator_dev **)data;
> +	struct max5970_regulator *ddata;
> +
> +	if (!rdevs || !rdevs[channel])

How can rdevs be NULL here ? Unless I am missing something, that can
only happen if its allocation in the probe function failed, but then
the system would long since have crashed before it gets here.

Also, rdevs[] only has as many entries as there are switches. That can
be 1 or 2. However, the hwmon subsystem will always assume that there are
two channels, because it is told so, and it will thus try to access rdevs[1]
even if only a single channel was allocated.

> +		return 0;
> +
> +	ddata = rdev_get_drvdata(rdevs[channel]);

With the above in mind, I wonder what that points to if channel == 1 and
ddata->num_switches == 1.

> +
> +	if (!ddata || channel >= ddata->num_switches)
> +		return 0;
> +
> +	switch (type) {
> +	case hwmon_in:
> +		switch (attr) {
> +		case hwmon_in_input:
> +			return 0444;
> +		default:
> +			break;
> +		}
> +		break;
> +	case hwmon_curr:
> +		switch (attr) {
> +		case hwmon_curr_input:
> +			/* Current measurement requires knowledge of the shunt resistor value. */
> +			if (ddata->shunt_micro_ohms)
> +				return 0444;
> +			break;
> +		default:
> +			break;
> +		}
> +		break;
> +	default:
> +		break;
> +	}
> +	return 0;
> +}
> +
> +static const struct hwmon_ops max5970_hwmon_ops = {
> +	.is_visible = max5970_is_visible,
> +	.read = max5970_read,
> +};
> +
> +static const struct hwmon_channel_info *max5970_info[] = {
> +	HWMON_CHANNEL_INFO(in, HWMON_I_INPUT, HWMON_I_INPUT),
> +	HWMON_CHANNEL_INFO(curr, HWMON_C_INPUT, HWMON_C_INPUT),
> +	NULL
> +};
> +
> +static const struct hwmon_chip_info max5970_chip_info = {
> +	.ops = &max5970_hwmon_ops,
> +	.info = max5970_info,
> +};
> +
>  static int max597x_uvp_ovp_check_mode(struct regulator_dev *rdev, int severity)
>  {
>  	int ret, reg;
> @@ -431,7 +554,8 @@ static int max597x_regulator_probe(struct platform_device *pdev)
>  	struct i2c_client *i2c = to_i2c_client(pdev->dev.parent);
>  	struct regulator_config config = { };
>  	struct regulator_dev *rdev;
> -	struct regulator_dev *rdevs[MAX5970_NUM_SWITCHES];
> +	struct regulator_dev **rdevs = NULL;
> +	struct device *hwmon_dev;
>  	int num_switches;
>  	int ret, i;
>  
> @@ -451,9 +575,10 @@ static int max597x_regulator_probe(struct platform_device *pdev)
>  	else
>  		return -ENODEV;
>  
> -	i2c_set_clientdata(i2c, max597x);
>  	num_switches = max597x->num_switches;
>  
> +	rdevs = devm_kcalloc(&i2c->dev, num_switches, sizeof(struct regulator_dev *), GFP_KERNEL);
> +

What if devm_kcalloc() returns NULL ?

>  	for (i = 0; i < num_switches; i++) {
>  		data =
>  		    devm_kzalloc(&i2c->dev, sizeof(struct max5970_regulator),
> @@ -485,6 +610,15 @@ static int max597x_regulator_probe(struct platform_device *pdev)
>  		max597x->shunt_micro_ohms[i] = data->shunt_micro_ohms;
>  	}
>  
> +	if (IS_REACHABLE(CONFIG_HWMON)) {
> +		hwmon_dev = devm_hwmon_device_register_with_info(&i2c->dev, "max5970", rdevs,
> +								 &max5970_chip_info, NULL);
> +		if (IS_ERR(hwmon_dev)) {
> +			return dev_err_probe(&i2c->dev, PTR_ERR(hwmon_dev),
> +					     "Unable to register hwmon device\n");
> +		}
> +	}
> +
>  	if (i2c->irq) {
>  		ret =
>  		    max597x_setup_irq(&i2c->dev, i2c->irq, rdevs, num_switches,

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