linux-kernel - Re: [PATCH v6 6/7] iio: adc: Add support for AD4000

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Message-ID: <152ba099-7610-478b-8465-49d9e5adffd0@sirena.org.uk>
Date: Mon, 1 Jul 2024 19:38:06 +0100
From: Mark Brown <broonie@...nel.org>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	Marcelo Schmitt <marcelo.schmitt@...log.com>, lars@...afoo.de,
	Michael.Hennerich@...log.com, robh+dt@...nel.org,
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
	nuno.sa@...log.com, dlechner@...libre.com, corbet@....net,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-spi@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 6/7] iio: adc: Add support for AD4000

On Mon, Jul 01, 2024 at 03:10:54PM -0300, Marcelo Schmitt wrote:
> On 06/30, Jonathan Cameron wrote:
> > Marcelo Schmitt <marcelo.schmitt@...log.com> wrote:

> > > +	struct spi_transfer t = {
> > > +		.tx_buf = st->tx_buf,
> > > +		.rx_buf = st->rx_buf,
> > > +		.len = 2,
> > > +	};

> > I'd be tempted to do

> > 	ssize_t ret;
> > 
> > 	ret = spi_w8r8(AD4000_READ_COMMAND);

> I tried this when working on v6. Only difference was I had declared ret as int.
> Then reg values were not read correctly with spi_w8r8().
> I'm either missing something or reg access must be 16-bit transfer.
> Datasheet sais:
> "The AD4000/AD4004/AD4008 configuration register is read from and written to
> with a 16-bit SPI instruction."
> Yet, besides possible delay between first and last 8 SCLK pulses, I don't see
> any transfer level differences between current and spi_w8r8() versions.

It is possible the chip gets upset with the state of the idle line
during the RX only or TX only portion of the transfer.

> 
> > 
> > 
> ...
> > > +			ret = ad4000_write_reg(st, reg_val);
> > > +			if (ret < 0)
> > > +				return ret;
> > > +
> > > +			st->span_comp = span_comp_en;
> > > +			return ret;
> > 
> > If you are spinning for another reason, make it clear this is always good.
> > The spi_write() never returns positive so current code is correct but I had
> > to go check which this would have avoided.
> > 
> > 			return 0;
> 
> Ack
> > 
> > If nothing else comes up, I'll probably tweak whilst applying.
> > 
> > J
> > 
> > > +		}
> > > +		unreachable();
> > > +	default:
> > > +		return -EINVAL;
> > > +	}
> > > +}
> > 

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