Re: [PATCH 2/2] hwmon: (lm75) Support active-high alert polarity

[Conor Dooley <conor@kernel.org>]

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On Fri, May 01, 2026 at 02:05:18PM +0200, Markus Stockhausen wrote:
> All chips supported by this driver support configurable active-high
> alert polarity. This is already documented in the devicetree description.
> Add support for it to the driver.
> 
> The default polarity of the devices is 0 (active-low). So there is
> no need to change the clear mask. For consistency reasons adapt the
> hard-coded configuration value of the AS6200. It is the only device
> that defaults to active-high polarity.

Uh, I dunno if you can do this, changing defaults is an ABI break
typically. What makes it okay to do that in this case?

> 
> Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
> ---
>  drivers/hwmon/lm75.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
> index f1a1e5b888f6..4b075a7b1cd7 100644
> --- a/drivers/hwmon/lm75.c
> +++ b/drivers/hwmon/lm75.c
> @@ -123,7 +123,9 @@ struct lm75_data {
>  
>  static const u8 lm75_sample_set_masks[] = { 0 << 5, 1 << 5, 2 << 5, 3 << 5 };
>  
> -#define LM75_SAMPLE_CLEAR_MASK	(3 << 5)
> +#define LM75_ALERT_POLARITY_HIGH_8_BIT	(BIT(2))
> +#define LM75_ALERT_POLARITY_HIGH_16_BIT	(BIT(2) << 8)
> +#define LM75_SAMPLE_CLEAR_MASK		(3 << 5)
>  
>  /* The structure below stores the configuration values of the supported devices.
>   * In case of being supported multiple configurations, the default one must
> @@ -137,7 +139,7 @@ static const struct lm75_params device_params[] = {
>  	},
>  	[as6200] = {
>  		.config_reg_16bits = true,
> -		.set_mask = 0x94C0,	/* 8 sample/s, 4 CF, positive polarity */
> +		.set_mask = 0x90C0,	/* 8 sample/s, 4 CF */
>  		.default_resolution = 12,
>  		.default_sample_time = 125,
>  		.num_sample_times = 4,
> @@ -728,6 +730,7 @@ static int lm75_generic_probe(struct device *dev, const char *name,
>  	struct device *hwmon_dev;
>  	struct lm75_data *data;
>  	int status, err;
> +	u16 set_mask;
>  
>  	data = devm_kzalloc(dev, sizeof(struct lm75_data), GFP_KERNEL);
>  	if (!data)
> @@ -762,8 +765,15 @@ static int lm75_generic_probe(struct device *dev, const char *name,
>  		return err;
>  	data->orig_conf = status;
>  
> -	err = lm75_write_config(data, data->params->set_mask,
> -				data->params->clr_mask);
> +	set_mask = data->params->set_mask;
> +	if (of_property_read_bool(dev->of_node, "lm75,alert-polarity-active-high")) {
> +		if (!data->params->config_reg_16bits)
> +			set_mask |= LM75_ALERT_POLARITY_HIGH_8_BIT;
> +		else
> +			set_mask |= LM75_ALERT_POLARITY_HIGH_16_BIT;
> +	}
> +
> +	err = lm75_write_config(data, set_mask, data->params->clr_mask);
>  	if (err)
>  		return err;
>  
> -- 
> 2.54.0
> 

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