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

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Message-ID: <CABqG17h8cpnFkdD-nnqyr+UnwADU9XWK6TGBxj_FCH37Y3Q1Lw@mail.gmail.com>
Date: Wed, 26 Mar 2025 22:06:53 +0530
From: Naresh Solanki <naresh.solanki@...ements.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (max6639) : Allow setting target RPM

Hi Guenter,

On Tue, 25 Mar 2025 at 05:00, Guenter Roeck <linux@...ck-us.net> wrote:
>
> 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.
Yes you're right. I missed it in my analysis.

Here is the logic that would address:
                target_rpm = 120;
                /* Set PWM based on target RPM if specified */
                if (data->target_rpm[i] != 0 &&
                    data->target_rpm[i]  <= rpm_ranges[data->rpm_range[i]]) {

                        target_duty = 120 * data->target_rpm[i] /
rpm_ranges[data->rpm_range[i]];
                }

Please let me know your thoughts & suggestions.

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