linux-kernel - Re: [PATCH v5 13/14] iio: adc: ad7768-1: add filter type and oversampling ratio attributes

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Message-ID: <20250412191126.06c19115@jic23-huawei>
Date: Sat, 12 Apr 2025 19:11:26 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Jonathan Santos <Jonathan.Santos@...log.com>
Cc: <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
 <lars@...afoo.de>, <Michael.Hennerich@...log.com>,
 <marcelo.schmitt@...log.com>, <robh@...nel.org>, <krzk+dt@...nel.org>,
 <conor+dt@...nel.org>, <marcelo.schmitt1@...il.com>,
 <linus.walleij@...aro.org>, <brgl@...ev.pl>, <lgirdwood@...il.com>,
 <broonie@...nel.org>, <jonath4nns@...il.com>, <dlechner@...libre.com>, Pop
 Paul <paul.pop@...log.com>
Subject: Re: [PATCH v5 13/14] iio: adc: ad7768-1: add filter type and
 oversampling ratio attributes



>  
> -static int ad7768_set_dig_fil(struct ad7768_state *st,
> -			      enum ad7768_dec_rate dec_rate)
> +static int ad7768_set_sinc3_dec_rate(struct ad7768_state *st,
> +				     unsigned int dec_rate)
>  {
> -	unsigned int mode;
> +	unsigned int max_dec_rate;
> +	u8 dec_rate_reg[2];
>  	int ret;
>  
> -	if (dec_rate == AD7768_DEC_RATE_8 || dec_rate == AD7768_DEC_RATE_16)
> -		mode = AD7768_DIG_FIL_FIL(dec_rate);
> -	else
> -		mode = AD7768_DIG_FIL_DEC_RATE(dec_rate);
> +	/*
> +	 * Maximum dec_rate is limited by the MCLK_DIV value
> +	 * and by the ODR. The edge case is for MCLK_DIV = 2
> +	 * ODR = 50 SPS.
> +	 * max_dec_rate <= MCLK / (2 * 50)
> +	 */
> +	max_dec_rate = st->mclk_freq / 100;
> +	dec_rate = clamp_t(unsigned int, dec_rate, 32, max_dec_rate);
> +	/*
> +	 * Calculate the equivalent value to sinc3 decimation ratio
> +	 * to be written on the SINC3_DECIMATION_RATE register:
> +	 *  Value = (DEC_RATE / 32) -1
> +	 */
> +	dec_rate = DIV_ROUND_UP(dec_rate, 32) - 1;
> +	dec_rate_reg[0] = FIELD_GET(AD7768_SINC3_DEC_RATE_MSB_MSK, dec_rate);
> +	dec_rate_reg[1] = FIELD_GET(AD7768_SINC3_DEC_RATE_LSB_MSK, dec_rate);
Looks like a larger big endian value. It's a little messy because of
the 12 bit mask but I think still clearer as

	u16 regval = FIELD_PREP(GENMASK(11, 0), dec_rate);
	
	unaligned_put_be16(dec_rate_reg, regval);

Avoids the use of masks to get bytes from the dec_rate value which is
is sort of backwards.


> +	ret = regmap_bulk_write(st->regmap, AD7768_REG_SINC3_DEC_RATE_MSB,
> +				dec_rate_reg, 2);
> +	if (ret)
> +		return ret;
>