linux-kernel - Re: [PATCH v2] iio:proximity:sx9324: Fix hardware gain read/write

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Date:   Sun, 27 Mar 2022 15:51:47 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Lars-Peter Clausen <lars@...afoo.de>, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, Gwendal Grignou <gwendal@...omium.org>
Subject: Re: [PATCH v2] iio:proximity:sx9324: Fix hardware gain read/write

On Thu, 24 Mar 2022 15:29:28 -0700
Stephen Boyd <swboyd@...omium.org> wrote:

> There are four possible gain values according to 'sx9324_gain_vals[]':
> 
> 	1, 2, 4, and 8
> 
> The values are off by one when writing and reading the register. The
> bits should be set according to this equation:
> 
> 	ilog2(<gain>) + 1
> 
> so that a gain of 8 is 0x3 in the register field and a gain of 4 is 0x2
> in the register field, etc

Example seems wrong... 

ilog2(8) + 1 = 3 + 1 = 0x4
ilog2(4) + 1 = 2 + 1 = 0x3
ilog2(2) + 1 = 1 + 1 = 0x2
ilog2(1) + 1 = 0 + 1 = 0x1
                       0x0 reserved.

or have I misunderstood?

>. Note that a gain of 0 is reserved per the
> datasheet. The default gain (SX9324_REG_PROX_CTRL0_GAIN_1) is also
> wrong. It should be 0x1 << 3, i.e. 0x8, not 0x80 which is setting the
> reserved bit 7.
> 
> Fix this all up to properly handle the hardware gain and return errors
> for invalid settings.
> 
> Fixes: 4c18a890dff8 ("iio:proximity:sx9324: Add SX9324 support")
> Cc: Gwendal Grignou <gwendal@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
> 
> Changes from v1 (https://lore.kernel.org/r/)20220318204808.3404542-1-swboyd@chromium.org:
>  * Reject invalid settings
>  * Fix default value
>  * More commit text details
> 
>  drivers/iio/proximity/sx9324.c | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
> index 0d9bbbb50cb4..6e90917e3e36 100644
> --- a/drivers/iio/proximity/sx9324.c
> +++ b/drivers/iio/proximity/sx9324.c
> @@ -76,7 +76,10 @@
>  
>  #define SX9324_REG_PROX_CTRL0		0x30
>  #define SX9324_REG_PROX_CTRL0_GAIN_MASK	GENMASK(5, 3)
> -#define SX9324_REG_PROX_CTRL0_GAIN_1		0x80
> +#define SX9324_REG_PROX_CTRL0_GAIN_SHIFT	3
> +#define SX9324_REG_PROX_CTRL0_GAIN_RSVD		0x0
> +#define SX9324_REG_PROX_CTRL0_GAIN_1		0x1
> +#define SX9324_REG_PROX_CTRL0_GAIN_8		0x4
>  #define SX9324_REG_PROX_CTRL0_RAWFILT_MASK	GENMASK(2, 0)
>  #define SX9324_REG_PROX_CTRL0_RAWFILT_1P50	0x01
>  #define SX9324_REG_PROX_CTRL1		0x31
> @@ -379,7 +382,14 @@ static int sx9324_read_gain(struct sx_common_data *data,
>  	if (ret)
>  		return ret;
>  
> -	*val = 1 << FIELD_GET(SX9324_REG_PROX_CTRL0_GAIN_MASK, regval);
> +	regval = FIELD_GET(SX9324_REG_PROX_CTRL0_GAIN_MASK, regval);
> +	if (regval)
> +		regval--;
> +	else if (regval == SX9324_REG_PROX_CTRL0_GAIN_RSVD ||
> +		 regval > SX9324_REG_PROX_CTRL0_GAIN_8)
> +		return -EINVAL;
> +
> +	*val = 1 << regval;
>  
>  	return IIO_VAL_INT;
>  }
> @@ -725,8 +735,12 @@ static int sx9324_write_gain(struct sx_common_data *data,
>  	unsigned int gain, reg;
>  	int ret;
>  
> -	gain = ilog2(val);
>  	reg = SX9324_REG_PROX_CTRL0 + chan->channel / 2;
> +
> +	gain = ilog2(val) + 1;
> +	if (val <= 0 || gain > SX9324_REG_PROX_CTRL0_GAIN_8)
> +		return -EINVAL;
> +
>  	gain = FIELD_PREP(SX9324_REG_PROX_CTRL0_GAIN_MASK, gain);
>  
>  	mutex_lock(&data->mutex);
> @@ -784,9 +798,11 @@ static const struct sx_common_reg_default sx9324_default_regs[] = {
>  	{ SX9324_REG_AFE_CTRL8, SX9324_REG_AFE_CTRL8_RESFILTN_4KOHM },
>  	{ SX9324_REG_AFE_CTRL9, SX9324_REG_AFE_CTRL9_AGAIN_1 },
>  
> -	{ SX9324_REG_PROX_CTRL0, SX9324_REG_PROX_CTRL0_GAIN_1 |
> +	{ SX9324_REG_PROX_CTRL0,
> +		SX9324_REG_PROX_CTRL0_GAIN_1 << SX9324_REG_PROX_CTRL0_GAIN_SHIFT |
>  		SX9324_REG_PROX_CTRL0_RAWFILT_1P50 },
> -	{ SX9324_REG_PROX_CTRL1, SX9324_REG_PROX_CTRL0_GAIN_1 |
> +	{ SX9324_REG_PROX_CTRL1,
> +		SX9324_REG_PROX_CTRL0_GAIN_1 << SX9324_REG_PROX_CTRL0_GAIN_SHIFT |
>  		SX9324_REG_PROX_CTRL0_RAWFILT_1P50 },
>  	{ SX9324_REG_PROX_CTRL2, SX9324_REG_PROX_CTRL2_AVGNEG_THRESH_16K },
>  	{ SX9324_REG_PROX_CTRL3, SX9324_REG_PROX_CTRL3_AVGDEB_2SAMPLES |
> 
> base-commit: a8ee3b32f5da6c77a5ccc0e42c2250d61ba54fe0