linux-kernel - Re: [PATCH] drivers: iio: adc: add support for ad777x family

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Date: Wed, 29 May 2024 18:11:33 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: "Nechita, Ramona" <Ramona.Nechita@...log.com>
Cc: "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"Hennerich, Michael" <Michael.Hennerich@...log.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, "Sa, Nuno" <Nuno.Sa@...log.com>,
	Marius Cristea <marius.cristea@...rochip.com>,
	"Schmitt, Marcelo" <Marcelo.Schmitt@...log.com>,
	Maksim Kiselev <bigunclemax@...il.com>,
	Ivan Mikhaylov <fr0st61te@...il.com>,
	Marcus Folkesson <marcus.folkesson@...il.com>,
	Liam Beguin <liambeguin@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers: iio: adc: add support for ad777x family

On Wed, May 29, 2024 at 03:01:06PM +0000, Nechita, Ramona wrote:

..

> >> +	/*
> >> +	 * DMA (thus cache coherency maintenance) requires the
> >> +	 * transfer buffers to live in their own cache lines.
> >> +	 */
> >> +	u8			reg_rx_buf[3] ____cacheline_aligned;
> >> +	u8			reg_tx_buf[3];
> >
> >> +	u8			spidata_rx[32];
> >> +	u8			spidata_tx[32];
> >
> >These will not be cache aligned. Is it a problem?
> 
> No, it should be fine without the alignment.

I.o.w. it means that only reg_*x_buf are supposed to be in the different cache lines, correct?

..

> >Btw, can't you use regmap for IO?
> 
> Unfortunately, I don't think regmap could be used, because of the crc and the
> fact that data is shifted out on the SPI SDO line in the interrupt. I
> consider perhaps adding regmap to the mix might complicate things a bit. 

Can you add this into the comment area of the patch?

..

> >> +	ret = ad777x_spi_write(st, AD777X_REG_SRC_N_LSB, lsb);
> >> +	if (ret)
> >> +		return ret;
> >> +	ret = ad777x_spi_write(st, AD777X_REG_SRC_N_MSB, msb);
> >> +	if (ret)
> >> +		return ret;
> >
> >Can you use 16-bit writes?
> >Same Q to all similar LSB/MSB write groups.
> 
> I cannot do 16-bit writes due to how the spi functions on the chip and
> because the registers for MSB/LSB are at different addresses.

They are supposed to be on the different addresses.
You mean the distance between them > than stride?

..

> >> +	ret = devm_add_action_or_reset(&spi->dev,
> >> +				       ad777x_clk_disable,
> >> +				       st->mclk);
> >> +	if (ret)
> >> +		return ret;
> >
> >So, what's wrong with the _enabled() API?
> 
> Sorry, I am not sure what you mean here by _enabled() API, is there a
> different mechanism that can be used for this type of operations?

devm_clk_get_enabled()

-- 
With Best Regards,
Andy Shevchenko