Message-ID: <CABqG17gZV7ZBKOz0gTsrfsuHQENF3VM2T-=O27sWdc1PP9OmPA@mail.gmail.com>
Date: Wed, 26 Mar 2025 22:29:33 +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 Wed, 26 Mar 2025 at 22:19, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 3/26/25 09:36, Naresh Solanki wrote:
> > 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.
> >
>
> I would prefer if target_rpm[] and rpm_range[] were pre-initialized with default
> values in the probe function. That would avoid runtime checks.
rpm_range is pre-initialized to 4000 RPM [1]
I can also init target_rpm[] to 4000 RPM as default along with above init.

But still there might be a case wherein DT doesn't provide max-rpm but
target-rpm is set to greater than 4000 RPM
Thus there will be a need to check to cover this kind of scenario.

Please let me know your thoughts & will implement that.

[1]https://kernel.googlesource.com/pub/scm/linux/kernel/git/groeck/linux-staging/+/hwmon-next/drivers/hwmon/max6639.c#586

Regards,
Naresh
>
> Thanks,
> Guenter
>

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