linux-kernel - Re: [PATCH RFC 2/5] iio: adc: ad4030: add driver for ad4030-24

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Message-Id: <D323OLK1T0CG.1OGNBVY1FDVJT@baylibre.com>
Date: Mon, 29 Jul 2024 16:42:16 +0200
From: "Esteban Blanc" <eblanc@...libre.com>
To: "Jonathan Cameron" <jic23@...nel.org>
Cc: "Lars-Peter Clausen" <lars@...afoo.de>, "Michael Hennerich"
 <Michael.Hennerich@...log.com>, "Rob Herring" <robh@...nel.org>, "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>, "Conor Dooley" <conor+dt@...nel.org>,
 "Nuno Sa" <nuno.sa@...log.com>, <linux-iio@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "David
 Lechner" <dlechner@...libre.com>
Subject: Re: [PATCH RFC 2/5] iio: adc: ad4030: add driver for ad4030-24

On Sat Jun 29, 2024 at 6:39 PM CEST, Jonathan Cameron wrote:
> On Thu, 27 Jun 2024 13:59:13 +0200
> Esteban Blanc <eblanc@...libre.com> wrote:
>
> > This adds a new driver for the Analog Devices INC. AD4030-24 ADC.
> > 
> > The driver implements basic support for the AD4030-24 1 channel
> > differential ADC with hardware gain and offset control.
> > 
> > Signed-off-by: Esteban Blanc <eblanc@...libre.com>

...

> > +static int ad4030_spi_read(void *context, const void *reg, size_t reg_size,
> > +			   void *val, size_t val_size)
> > +{
> > +	struct ad4030_state *st = context;
> > +
> > +	struct spi_transfer xfer = {
> > +		.tx_buf = st->tx_data,
> > +		.rx_buf = st->rx_data.raw,
> > +		.len = reg_size + val_size,
> > +	};
> > +	int ret;
> > +
> > +	memcpy(st->tx_data, reg, reg_size);
> > +
> > +	ret = spi_sync_transfer(st->spi, &xfer, 1);
> > +	if (ret)
> > +		return ret;
> > +
> > +	memcpy(val, &st->rx_data.raw[reg_size], val_size);
>
> Can you just use spi_write_then_read() here?
>

I was planning on doing that. But I'm getting a timeout issue when
using `spi_write_then_read`. I can see the tx_data going out, rx_data
is recived but CS is kept asserted. I need to investigate more but in
the meantime I'm using this as it is working. I will remove this
workaround if I can find a fix and add a comment for now.

> > +	if (ret)
> > +		return ret;
> > +
> > +	if (st->chip->precision_bits == 16)
> > +		offset <<= 16;
> > +	else
> > +		offset <<= 8;
>
> As below. This is hard tor read. Just use appropriate unaligned gets for the
> two cases to extract the write bytes directly.
>
> > +	*val = be32_to_cpu(offset);
> > +
> > +	return 0;
> > +}
> > +
> > +static int ad4030_set_chan_gain(struct iio_dev *indio_dev, int ch, int gain_int,
> > +				int gain_frac)
> > +{
> > +	struct ad4030_state *st = iio_priv(indio_dev);
> > +	__be16 val;
> > +	u64 gain;
> > +
> > +	gain = mul_u32_u32(gain_int, MICRO) + gain_frac;
> > +
> > +	if (gain > AD4030_REG_GAIN_MAX_GAIN)
> > +		return -EINVAL;
> > +
> > +	val = cpu_to_be16(DIV_ROUND_CLOSEST_ULL(gain * 0x8000, MICRO));
> > +
> > +	return regmap_bulk_write(st->regmap, AD4030_REG_GAIN_CHAN(ch), &val,
> > +			  AD4030_REG_GAIN_BYTES_NB);
> > +}
> > +
> > +static int ad4030_set_chan_offset(struct iio_dev *indio_dev, int ch, int offset)
> > +{
> > +	struct ad4030_state *st = iio_priv(indio_dev);
> > +	__be32 val;
> > +
> > +	if (offset < st->min_offset || offset > st->max_offset)
> > +		return -EINVAL;
> > +
> > +	val = cpu_to_be32(offset);
> > +	if (st->chip->precision_bits == 16)
> > +		val >>= 16;
> > +	else
> > +		val >>= 8;
>
> I 'think' I get what this is doing but not 100% sure as it's a bit too unusual
> and I'm not even sure what happens if we shift a __be32 value on a little endian
> system. I would instead split this into appropriate cpu_to_be24() and cpu_to_be16()
> to put the value directly in the right place rather than shifting in place.

cpu_to_be24 does not exist yet. I will have a look on how to add them.


All the other comments will be addressed in V2.

Best regards,

-- 
Esteban "Skallwar" Blanc
BayLibre