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

[Guenter Roeck]

On 3/26/25 09:36, Naresh Solanki wrote:
> Hi Guenter,
>
> On Tue, 25 Mar 2025 at 05:00, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 3/24/25 11:57, Your Name wrote:
> > > From: Naresh Solanki <naresh.solanki@xxxxxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxxxx>
> > > ---
> > >    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.

I would prefer if target_rpm[] and rpm_range[] were pre-initialized with default
values in the probe function. That would avoid runtime checks.

Thanks,
Guenter