linux-kernel - Re: [PATCH v1 2/2] hwmon: (amc6821) Add PWM polarity configuration with OF

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Message-ID: <20250219161611.GB22470@francesco-nb>
Date: Wed, 19 Feb 2025 17:16:11 +0100
From: Francesco Dolcini <francesco@...cini.it>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Quentin Schulz <quentin.schulz@...rry.de>,
	Francesco Dolcini <francesco@...cini.it>,
	Jean Delvare <jdelvare@...e.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Farouk Bouabid <farouk.bouabid@...rry.de>,
	Francesco Dolcini <francesco.dolcini@...adex.com>,
	linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] hwmon: (amc6821) Add PWM polarity configuration
 with OF

On Wed, Feb 19, 2025 at 05:46:10AM -0800, Guenter Roeck wrote:
> On 2/19/25 02:08, Quentin Schulz wrote:
> > Hi Francesco,
> > 
> > On 2/18/25 5:56 PM, Francesco Dolcini wrote:
> > > From: Francesco Dolcini <francesco.dolcini@...adex.com>
> > > 
> > > Add support to configure the PWM-Out pin polarity based on a device
> > > tree property.
> > > 
> > > Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> > > ---
> > >   drivers/hwmon/amc6821.c | 7 +++++--
> > >   1 file changed, 5 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c
> > > index 1e3c6acd8974..1ea2d97eebca 100644
> > > --- a/drivers/hwmon/amc6821.c
> > > +++ b/drivers/hwmon/amc6821.c
> > > @@ -845,7 +845,7 @@ static int amc6821_detect(struct i2c_client *client, struct i2c_board_info *info
> > >       return 0;
> > >   }
> > > -static int amc6821_init_client(struct amc6821_data *data)
> > > +static int amc6821_init_client(struct i2c_client *client, struct amc6821_data *data)
> > >   {
> > >       struct regmap *regmap = data->regmap;
> > >       int err;
> > > @@ -864,6 +864,9 @@ static int amc6821_init_client(struct amc6821_data *data)
> > >           if (err)
> > >               return err;
> > > +        if (of_property_read_bool(client->dev.of_node, "ti,pwm-inverted"))
> > 
> > I know that the AMC6821 is doing a lot of smart things, but this really tickled me. PWM controllers actually do support that already via PWM_POLARITY_INVERTED flag for example. See Documentation/devicetree/bindings/hwmon/adt7475.yaml which seems to be another HWMON driver which acts as a PWM controller. I'm not sure this is relevant, applicable or desired but I wanted to highlight this.
> > 
> > > +            pwminv = 1;
> > > +
> > 
> > This is silently overriding the module parameter.
> > 
> > I don't think this is a good idea, at the very least not silently.
> > 
> > I would suggest to add some logic in the probe function to set this value and check its consistency.
> > 
> > Something like:
> > 
> > """
> > diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c
> > index 1e3c6acd89740..3a13a914e2bbb 100644
> > --- a/drivers/hwmon/amc6821.c
> > +++ b/drivers/hwmon/amc6821.c
> > @@ -37,7 +37,7 @@ static const unsigned short normal_i2c[] = {0x18, 0x19, 0x1a, 0x2c, 0x2d, 0x2e,
> >    * Insmod parameters
> >    */
> > 
> > -static int pwminv;    /*Inverted PWM output. */
> > +static int pwminv = -1;    /* -1 not modified by the user, 0 default PWM output, 1 inverted PWM output */
> >   module_param(pwminv, int, 0444);
> > 
> >   static int init = 1; /*Power-on initialization.*/
> > @@ -904,6 +904,7 @@ static int amc6821_probe(struct i2c_client *client)
> >       struct amc6821_data *data;
> >       struct device *hwmon_dev;
> >       struct regmap *regmap;
> > +    bool pwminv_dt;
> >       int err;
> > 
> >       data = devm_kzalloc(dev, sizeof(struct amc6821_data), GFP_KERNEL);
> > @@ -916,6 +917,18 @@ static int amc6821_probe(struct i2c_client *client)
> >                        "Failed to initialize regmap\n");
> >       data->regmap = regmap;
> > 
> > +    pwminv_dt = of_property_read_bool(client->dev.of_node, "ti,pwm-inverted");
> > +
> > +    if (pwminv == -1) {
> > +        pwminv = pwminv_dt;
> 
> A devicetree property, associated with a single instance of the driver,
> overriding a module parameter affecting all instances ? This is a no-go.

I will rework the patch in such a way that the module parameter, when
specified, takes always the precedence over the DT code, works for you
Guenter ?

Francesco