linux-kernel - Re: [PATCH v4 2/3] iio: dps310: Temperature measurement errata

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Date:   Sun, 26 May 2019 18:34:49 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Eddie James <eajames@...ux.ibm.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        joel@....id.au, lars@...afoo.de, knaack.h@....de,
        Christopher Bostic <cbostic@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 2/3] iio: dps310: Temperature measurement errata

On Mon, 20 May 2019 21:13:33 -0500
Eddie James <eajames@...ux.ibm.com> wrote:

> From: Christopher Bostic <cbostic@...ux.vnet.ibm.com>
> 
> Add a manufacturer's suggested workaround to deal with early revisions
> of chip that don't indicate correct temperature. Readings can be in the
> ~60C range when they should be in the ~20's.
> 
> Signed-off-by: Christopher Bostic <cbostic@...ux.vnet.ibm.com>
> Signed-off-by: Joel Stanley <joel@....id.au>
> Signed-off-by: Eddie James <eajames@...ux.ibm.com>
> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
>  drivers/iio/pressure/dps310.c | 52 +++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
> index 9acfccb..a093e3a 100644
> --- a/drivers/iio/pressure/dps310.c
> +++ b/drivers/iio/pressure/dps310.c
> @@ -53,7 +53,6 @@
>  #define DPS310_RESET		0x0c
>  #define  DPS310_RESET_MAGIC	0x09
>  #define DPS310_COEF_BASE	0x10
> -#define DPS310_COEF_SRC		0x28
>  
>  /* Make sure sleep time is <= 20ms for usleep_range */
>  #define DPS310_POLL_SLEEP_US(t)		min(20000, (t) / 8)
> @@ -234,6 +233,10 @@ static bool dps310_is_writeable_reg(struct device *dev, unsigned int reg)
>  	case DPS310_MEAS_CFG:
>  	case DPS310_CFG_REG:
>  	case DPS310_RESET:
> +	/* No documentation available on the registers below */
> +	case 0x0e:
> +	case 0x0f:
> +	case 0x62:
>  		return true;
>  	default:
>  		return false;
> @@ -250,6 +253,7 @@ static bool dps310_is_volatile_reg(struct device *dev, unsigned int reg)
>  	case DPS310_TMP_B1:
>  	case DPS310_TMP_B2:
>  	case DPS310_MEAS_CFG:
> +	case 0x32:	/* No documentation available on this register */
>  		return true;
>  	default:
>  		return false;
> @@ -360,7 +364,7 @@ static void dps310_reset(void *action_data)
>  	.writeable_reg = dps310_is_writeable_reg,
>  	.volatile_reg = dps310_is_volatile_reg,
>  	.cache_type = REGCACHE_RBTREE,
> -	.max_register = DPS310_COEF_SRC,
> +	.max_register = 0x62, /* No documentation available on this register */
>  };
>  
>  static const struct iio_info dps310_info = {
> @@ -368,6 +372,46 @@ static void dps310_reset(void *action_data)
>  	.write_raw = dps310_write_raw,
>  };
>  
> +/*
> + * Some verions of chip will read temperatures in the ~60C range when
> + * its actually ~20C. This is the manufacturer recommended workaround
> + * to correct the issue. The registers used below are undocumented.
> + */
> +static int dps310_temp_workaround(struct dps310_data *data)
> +{
> +	int rc;
> +	int reg;
> +
> +	rc = regmap_read(data->regmap, 0x32, &reg);
> +	if (rc < 0)
> +		return rc;
> +
> +	/*
> +	 * If bit 1 is set then the device is okay, and the workaround does not
> +	 * need to be applied
> +	 */
> +	if (reg & BIT(1))
> +		return 0;
> +
> +	rc = regmap_write(data->regmap, 0x0e, 0xA5);
> +	if (rc < 0)
> +		return rc;
> +
> +	rc = regmap_write(data->regmap, 0x0f, 0x96);
> +	if (rc < 0)
> +		return rc;
> +
> +	rc = regmap_write(data->regmap, 0x62, 0x02);
> +	if (rc < 0)
> +		return rc;
> +
> +	rc = regmap_write(data->regmap, 0x0e, 0x00);
> +	if (rc < 0)
> +		return rc;
> +
> +	return regmap_write(data->regmap, 0x0f, 0x00);
> +}
> +
>  static int dps310_probe(struct i2c_client *client,
>  			const struct i2c_device_id *id)
>  {
> @@ -439,6 +483,10 @@ static int dps310_probe(struct i2c_client *client,
>  	if (rc < 0)
>  		return rc;
>  
> +	rc = dps310_temp_workaround(data);
> +	if (rc < 0)
> +		return rc;
> +
>  	rc = devm_iio_device_register(&client->dev, iio);
>  	if (rc)
>  		return rc;