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

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Message-ID: <07ec64e7-041d-4f5a-a04c-daa4b0794111@roeck-us.net>
Date: Wed, 19 Feb 2025 05:46:10 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: 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>
Cc: 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 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.

Guenter