linux-kernel - Re: [PATCH 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

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Message-ID: <a6ae372e-e0c9-4874-8be1-8070ee3e880f@baylibre.com>
Date: Tue, 2 Sep 2025 10:14:52 -0500
From: David Lechner <dlechner@...libre.com>
To: Matti Vaittinen <mazziesaccount@...il.com>,
 Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Linus Walleij
 <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>,
 Marcelo Schmitt <marcelo.schmitt@...log.com>,
 Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Tobias Sperling <tobias.sperling@...ting.com>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>,
 Trevor Gamblin <tgamblin@...libre.com>, Esteban Blanc <eblanc@...libre.com>,
 Ramona Alexandra Nechita <ramona.nechita@...log.com>,
 Thomas Bonnefille <thomas.bonnefille@...tlin.com>,
 Hans de Goede <hansg@...nel.org>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org
Subject: Re: [PATCH 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

On 9/2/25 7:24 AM, Matti Vaittinen wrote:
> The ROHM BD79112 is an ADC/GPIO with 32 channels. The channel inputs can
> be used as ADC or GPIO. Using the GPIOs as IRQ sources isn't supported.
> 
> The ADC is 12-bit, supporting input voltages up to 5.7V, and separate I/O
> voltage supply. Maximum SPI clock rate is 20 MHz (10 MHz with
> daisy-chain configuration) and maximum sampling rate is 1MSPS.
> 
> The IC does also support CRC but it is not implemented in the driver.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> ---
>  drivers/iio/adc/Kconfig        |  10 +
>  drivers/iio/adc/Makefile       |   1 +
>  drivers/iio/adc/rohm-bd79112.c | 542 +++++++++++++++++++++++++++++++++
>  3 files changed, 553 insertions(+)
>  create mode 100644 drivers/iio/adc/rohm-bd79112.c
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index e3d3826c3357..4b78929bb257 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -1309,6 +1309,16 @@ config RN5T618_ADC
>  	  This driver can also be built as a module. If so, the module
>  	  will be called rn5t618-adc.
>  
> +config ROHM_BD79112
> +	tristate "Rohm BD79112 ADC driver"
> +	depends on I2C && GPIOLIB
> +	select REGMAP_I2C

I think you want SPI rather than I2C. :-)

> +	select IIO_ADC_HELPER
> +	help
> +	  Say yes here to build support for the ROHM BD79112 ADC. The
> +	  ROHM BD79112 is a 12-bit, 32-channel, SAR ADC, which analog
> +	  inputs can also be used for GPIO.
> +



> +struct bd79112_data {
> +	struct spi_device *spi;
> +	struct regmap *map;
> +	struct device *dev;
> +	struct gpio_chip gc;
> +	unsigned long gpio_valid_mask;
> +	unsigned int vref_mv;
> +	struct spi_transfer read_xfer[2];
> +	struct spi_transfer write_xfer;
> +	struct spi_message read_msg;
> +	struct spi_message write_msg;
> +	/* 16-bit TX, valid data in high byte */
> +	u8 read_tx[2] __aligned(IIO_DMA_MINALIGN);
> +	/* 8-bit address followed by 8-bit data */
> +	u8 reg_write_tx[2] __aligned(IIO_DMA_MINALIGN);
> +	/* 12-bit of ADC data or 8 bit of reg data */
> +	__be16 read_rx __aligned(IIO_DMA_MINALIGN);

Usually, we only need one __aligned(IIO_DMA_MINALIGN) (on the first
field). Since these are only used for SPI messages and we can only
send one message at a time, there isn't a way for there to be a
problem that would require them to each need to be in their own
cache line.

> +};
> +



> +static int bd79112_probe(struct spi_device *spi)
> +{

...

> +	iio_dev->channels = cs;
> +	iio_dev->num_channels = ret;

This is quite far from where it is assigned. Better to have a dedicated
local variable for this.

> +	iio_dev->info = &bd79112_info;
> +	iio_dev->name = "bd79112";
> +	iio_dev->modes = INDIO_DIRECT_MODE;
> +