linux-kernel - Re: [PATCH 2/2] iio: dac: support the ad8460 Waveform DAC

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Message-ID: <20240628194546.2f608365@jic23-huawei>
Date: Fri, 28 Jun 2024 19:45:46 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: "Tinaco, Mariel" <Mariel.Tinaco@...log.com>
Cc: "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Lars-Peter
 Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Liam
 Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 "Hennerich, Michael" <Michael.Hennerich@...log.com>, Marcelo Schmitt
 <marcelo.schmitt1@...il.com>, Dimitri Fedrau <dima.fedrau@...il.com>,
 Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH 2/2] iio: dac: support the ad8460 Waveform DAC

> > > +};
> > > +
> > > +static int ad8460_get_powerdown_mode(struct iio_dev *indio_dev,
> > > +				     const struct iio_chan_spec *chan) {
> > > +	return 0;  
> > 
> > Why have the stubs in here?  
> 
> Should I move the stubs to a different place in the code or remove them
> altogether since there is only a single powerdown mode available
Ah. I'd not really understood what was going on here.  This is fine as
is.

> > AD8460_HVDAC_DATA_WORD_HIGH(index),  
> > > +			    ((val >> 8) & 0xFF));  
> > 
> > bulk write? or do these need to be ordered?  
> 
> For this I used bulk read/write this way.
> 
> static int ad8460_set_hvdac_word(struct ad8460_state *state,
> 				 int index,
> 				 int val)
> {
> 	u8 regvals[AD8460_DATA_BYTE_WORD_LENGTH];
regmap bulk accesses (when spi anyway) should be provided with DMA safe buffers.
Easiest way to do that is add one with __aligned(IIO_DMA_MINALIGN) to the end
of the ad8460_state structure.  Possibly you'll need a lock to protect it - I haven't
checked.
> 
> 	regvals[0] = val & 0xFF;
> 	regvals[1] = (val >> 8) & 0xFF;

That is an endian conversion so use appropriate endian function to fill it efficiently
and document clearly what is going on.


	put_unaligned_le16()

> 
> 	return regmap_bulk_write(state->regmap, AD8460_HVDAC_DATA_WORD_LOW(index),
> 				 regvals, AD8460_DATA_BYTE_WORD_LENGTH);
> }
> 
> 
> > > +}

> > > +	state->regmap = devm_regmap_init_spi(spi, &ad8460_regmap_config);
> > > +	if (IS_ERR(state->regmap))
> > > +		return dev_err_probe(&spi->dev, PTR_ERR(state->regmap),
> > > +				     "Failed to initialize regmap");
> > > +
> > > +	ret = devm_iio_dmaengine_buffer_setup_ext(&spi->dev, indio_dev, "tx",
> > > +  
> > IIO_BUFFER_DIRECTION_OUT);
> > 
> > Ah. I take back my binding comment. I assume this is mapping some non
> > standard interface for the parallel data flow?  
> 
> Yes, the HDL side doesn't follow yet the standard IIO backend from which this
> driver was tested

Hmm. I'd like to see this brought inline with the other iio backend
drivers if possible.

Jonathan