linux-kernel - Re: [PATCH] hwmon: (max6639) : Allow setting target RPM

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Message-ID: <b6668968-897f-4864-913c-d4d557f1d7cc@roeck-us.net>
Date: Mon, 24 Mar 2025 16:30:10 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Your Name <naresh.solanki@...ements.com>, Jean Delvare
 <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (max6639) : Allow setting target RPM

On 3/24/25 11:57, Your Name wrote:
> From: Naresh Solanki <naresh.solanki@...ements.com>
> 
> Currently, during startup, the fan is set to its maximum RPM by default,
> which may not be suitable for all use cases.
> This patch introduces support for specifying a target RPM via the Device
> Tree property "target-rpm".
> 
> Changes:
> - Added `target_rpm` field to `max6639_data` structure to store the
>    target RPM for each fan channel.
> - Modified `max6639_probe_child_from_dt()` to read the `"target-rpm"`
>    property from the Device Tree and set `target_rpm` accordingly.
> - Updated `max6639_init_client()` to use `target_rpm` to compute the
>    initial PWM duty cycle instead of defaulting to full speed (120/120).
> 
> Behavior:
> - If `"target-rpm"` is specified, the fan speed is set accordingly.
> - If `"target-rpm"` is not specified, the previous behavior (full speed
>    at startup) is retained.
> 

Unless I am missing something, that is not really correct. See below.

> This allows better control over fan speed during system initialization.
> 
> Signed-off-by: Naresh Solanki <naresh.solanki@...ements.com>
> ---
>   drivers/hwmon/max6639.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/max6639.c b/drivers/hwmon/max6639.c
> index 32b4d54b2076..ca8a8f58d133 100644
> --- a/drivers/hwmon/max6639.c
> +++ b/drivers/hwmon/max6639.c
> @@ -80,6 +80,7 @@ struct max6639_data {
>   	/* Register values initialized only once */
>   	u8 ppr[MAX6639_NUM_CHANNELS];	/* Pulses per rotation 0..3 for 1..4 ppr */
>   	u8 rpm_range[MAX6639_NUM_CHANNELS]; /* Index in above rpm_ranges table */
> +	u32 target_rpm[MAX6639_NUM_CHANNELS];
>   
>   	/* Optional regulator for FAN supply */
>   	struct regulator *reg;
> @@ -560,8 +561,14 @@ static int max6639_probe_child_from_dt(struct i2c_client *client,
>   	}
>   

target_rpm[] is 0 here.

>   	err = of_property_read_u32(child, "max-rpm", &val);
> -	if (!err)
> +	if (!err) {
>   		data->rpm_range[i] = rpm_range_to_reg(val);
> +		data->target_rpm[i] = val;
> +	}

If there is no max-rpm property, or if there is no devicetree support,
target_rpm[i] is still 0.

> +
> +	err = of_property_read_u32(child, "target-rpm", &val);
> +	if (!err)
> +		data->target_rpm[i] = val;

If there is neither max-rpm nor target-rpm, target_rpm[i] is still 0.

>   
>   	return 0;
>   }
> @@ -573,6 +580,7 @@ static int max6639_init_client(struct i2c_client *client,
>   	const struct device_node *np = dev->of_node;
>   	struct device_node *child;
>   	int i, err;
> +	u8 target_duty;
>   
>   	/* Reset chip to default values, see below for GCONFIG setup */
>   	err = regmap_write(data->regmap, MAX6639_REG_GCONFIG, MAX6639_GCONFIG_POR);
> @@ -639,8 +647,9 @@ static int max6639_init_client(struct i2c_client *client,
>   		if (err)
>   			return err;
>   
> -		/* PWM 120/120 (i.e. 100%) */
> -		err = regmap_write(data->regmap, MAX6639_REG_TARGTDUTY(i), 120);
> +		/* Set PWM based on target RPM if specified */
> +		target_duty = 120 * data->target_rpm[i] / rpm_ranges[data->rpm_range[i]];

If there is no devicetree support, or if neither max-rpm nor target-rpm are
provided, target_duty will be 0, and the fans will stop.

Maybe my interpretation is wrong, but I think both target_rpm[] and rpm_range[]
will need to be initialized. Also, it seems to me that there will need to be an
upper bound for target_rpm[]; without it, it is possible that target_duty > 120,
which would probably not be a good idea.

Guenter

> +		err = regmap_write(data->regmap, MAX6639_REG_TARGTDUTY(i), target_duty);
>   		if (err)
>   			return err;
>   	}
> 
> base-commit: 2115cbeec8a3ccc69e3b7ecdf97b4472b0829cfc