linux-kernel - Re: [PATCH v4 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

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Message-ID: <92306c8a-a2ec-4a43-80d7-c8e0c1cc0ee1@baylibre.com>
Date: Thu, 11 Sep 2025 16:20:50 -0500
From: David Lechner <dlechner@...libre.com>
To: Matti Vaittinen <mazziesaccount@...il.com>,
 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>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v4 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

On 9/10/25 6:24 AM, Matti Vaittinen wrote:

...

> diff --git a/drivers/iio/adc/rohm-bd79112.c b/drivers/iio/adc/rohm-bd79112.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..a2a3affe2c6dc86a237a164139c27ec66dc9d131
> --- /dev/null
> +++ b/drivers/iio/adc/rohm-bd79112.c
> @@ -0,0 +1,553 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * ROHM ADC driver for BD79112 signal monitoring hub.
> + * Copyright (C) 2025, ROHM Semiconductor.
> + *
> + * SPI communication derived from ad7923.c and ti-ads7950.c

Really? I wrote the ti-ads7950 driver and I can't say I see the
resemblance. ;-)

> + */
> +

...

> +static int bd79112_get_gpio_pins(const struct iio_chan_spec *cs, int num_channels)

u32 would make more sense when dealing with bit flags.

> +{
> +	int i, gpio_channels;

same for the local variable.

...

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

...

> +
> +	data->read_xfer[0].tx_buf = &data->read_tx[0];
> +	data->read_xfer[0].len = sizeof(data->read_tx);
> +	data->read_xfer[0].cs_change = 1;
> +	data->read_xfer[1].rx_buf = &data->read_rx;
> +	data->read_xfer[1].len = sizeof(data->read_rx);
> +	spi_message_init_with_transfers(&data->read_msg, data->read_xfer, 2);
> +
> +	data->write_xfer.tx_buf = &data->reg_write_tx[0];
> +	data->write_xfer.len = sizeof(data->reg_write_tx);
> +	spi_message_init_with_transfers(&data->write_msg, &data->write_xfer, 1);

If these messages never change (other than the data in the buffers), you can
call devm_spi_optimize_message() here on each message to get reduced CPU usage
on every SPI message for free.