linux-kernel - Re: [PATCH] Input: pixcir_i2c_ts - add support for one-time total calibration

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Message-ID: <5uyos6zu74jfro7zsfup4zbkrywf5odi4ytfuwuttslgrus2of@fmopwef7fkme>
Date: Tue, 18 Nov 2025 11:26:03 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Michal Vokáč <michal.vokac@...ft.com>
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH] Input: pixcir_i2c_ts - add support for one-time total
 calibration

Hi Michal,

On Wed, Nov 12, 2025 at 02:00:19PM +0100, Michal Vokáč wrote:
> The Pixcir Tango controller has support for a one-time total calibration
> (manual calibration) procedure. Its purpose is to measure the capacitance
> offsets of the electrode system and to store these values into EEPROM.
> 
> During normal operation this calibration data is subtracted from the values
> measured. This calibration should be necessary only once in the product
> lifetime. It should be performed as part of the final adjustment after
> the panel is mounted in the product.
> 
> Add support for the calibration with sysfs interface.
> 
> Signed-off-by: Michal Vokáč <michal.vokac@...ft.com>
> ---
>  drivers/input/touchscreen/pixcir_i2c_ts.c | 34 +++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/drivers/input/touchscreen/pixcir_i2c_ts.c b/drivers/input/touchscreen/pixcir_i2c_ts.c
> index dad5786e82a4..2215e56b1458 100644
> --- a/drivers/input/touchscreen/pixcir_i2c_ts.c
> +++ b/drivers/input/touchscreen/pixcir_i2c_ts.c
> @@ -24,6 +24,7 @@
>   */
>  #define PIXCIR_REG_POWER_MODE	51
>  #define PIXCIR_REG_INT_MODE	52
> +#define PIXCIR_REG_SPECOP	58
>  
>  /*
>   * Power modes:
> @@ -82,6 +83,7 @@ struct pixcir_i2c_ts_data {
>  	const struct pixcir_i2c_chip_data *chip;
>  	struct touchscreen_properties prop;
>  	bool running;
> +	struct mutex sysfs_mutex;
>  };
>  
>  struct pixcir_report_data {
> @@ -462,6 +464,35 @@ static int pixcir_i2c_ts_resume(struct device *dev)
>  static DEFINE_SIMPLE_DEV_PM_OPS(pixcir_dev_pm_ops,
>  				pixcir_i2c_ts_suspend, pixcir_i2c_ts_resume);
>  
> +static ssize_t calibrate_store(struct device *dev,
> +			       struct device_attribute *attr,
> +			       const char *buf, size_t count)
> +{
> +	struct i2c_client *client = to_i2c_client(dev);
> +	struct pixcir_i2c_ts_data *ts = i2c_get_clientdata(client);
> +	static const u8 cmd = 0x03;
> +	int error;
> +
> +	error = mutex_lock_interruptible(&ts->sysfs_mutex);
> +	if (error)
> +		return error;

Why do we need this mutex? i2c_smbus_write_byte_data() does take adapter
lock, why do we need this additional locking?

Thanks.

-- 
Dmitry