linux-kernel - Re: [PATCH] iio: light: vcnl4000: Set ps high definition for 4040/4200

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Date: Tue, 26 Dec 2023 16:19:34 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Mårten Lindahl <marten.lindahl@...s.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, <linux-iio@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <kernel@...s.com>
Subject: Re: [PATCH] iio: light: vcnl4000: Set ps high definition for
 4040/4200

On Thu, 21 Dec 2023 17:33:09 +0100
Mårten Lindahl <marten.lindahl@...s.com> wrote:

> The vcnl4040/vcnl4200 proximity sensor defaults to 12 bit data
> resolution, but the chip also supports 16 bit data resolution, which is
> called proximity high definition (PS_HD).
> 
> Make the vcnl4040/vcnl4200 proximity sensor use the high definition for
> all data readings.
> 
> Signed-off-by: Mårten Lindahl <marten.lindahl@...s.com>

Hmm. Was about to apply this and had a nasty thought.  Whilst proximity isn't
'scaled' as such because there is no absolute scale applied, I assume this change
divides the effective scale (so what someone may be applying in userspace) by 16?

So this might cause someone a visible userspace regression?

If so we may have to report it IIO_VAL_FRACTIONAL with the bottom set to 16
so we end up with a suitable fixed point value from sysfs.

Jonathan

> ---
>  drivers/iio/light/vcnl4000.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/iio/light/vcnl4000.c b/drivers/iio/light/vcnl4000.c
> index fdf763a04b0b..4846f3b698b5 100644
> --- a/drivers/iio/light/vcnl4000.c
> +++ b/drivers/iio/light/vcnl4000.c
> @@ -90,6 +90,7 @@
>  #define VCNL4040_PS_CONF1_PS_SHUTDOWN	BIT(0)
>  #define VCNL4040_PS_CONF2_PS_IT	GENMASK(3, 1) /* Proximity integration time */
>  #define VCNL4040_CONF1_PS_PERS	GENMASK(5, 4) /* Proximity interrupt persistence setting */
> +#define VCNL4040_PS_CONF2_PS_HD		BIT(11)	/* Proximity high definition */
>  #define VCNL4040_PS_CONF2_PS_INT	GENMASK(9, 8) /* Proximity interrupt mode */
>  #define VCNL4040_PS_CONF3_MPS		GENMASK(6, 5) /* Proximity multi pulse number */
>  #define VCNL4040_PS_MS_LED_I		GENMASK(10, 8) /* Proximity current */
> @@ -345,6 +346,7 @@ static int vcnl4200_set_power_state(struct vcnl4000_data *data, bool on)
>  static int vcnl4200_init(struct vcnl4000_data *data)
>  {
>  	int ret, id;
> +	u16 regval;
>  
>  	ret = i2c_smbus_read_word_data(data->client, VCNL4200_DEV_ID);
>  	if (ret < 0)
> @@ -389,6 +391,17 @@ static int vcnl4200_init(struct vcnl4000_data *data)
>  	mutex_init(&data->vcnl4200_al.lock);
>  	mutex_init(&data->vcnl4200_ps.lock);
>  
> +	/* Use 16 bits proximity sensor readings */
> +	ret = i2c_smbus_read_word_data(data->client, VCNL4200_PS_CONF1);
> +	if (ret >= 0) {
> +		regval = (ret | VCNL4040_PS_CONF2_PS_HD);
> +		ret = i2c_smbus_write_word_data(data->client, VCNL4200_PS_CONF1,
> +						regval);
> +	}
> +
> +	if (ret < 0)
> +		dev_info(&data->client->dev, "Default to 12 bits sensor data");
> +
>  	ret = data->chip_spec->set_power_state(data, true);
>  	if (ret < 0)
>  		return ret;
> 
> ---
> base-commit: a39b6ac3781d46ba18193c9dbb2110f31e9bffe9
> change-id: 20231221-vcnl4000-ps-hd-863f4f8fcea7
> 
> Best regards,