Re: [PATCH v9 2/6] iio: adc: ad4691: add initial driver for AD4691 family

Jonathan Cameron
2026-05-05T13:23:42Z

On Thu, 30 Apr 2026 13:16:44 +0300
Radu Sabau via B4 Relay <devnull+radu.sabau.analog.com@kernel.org> wrote:

> From: Radu Sabau <radu.sabau@analog.com>
>
> Add support for the Analog Devices AD4691 family of high-speed,
> low-power multichannel SAR ADCs: AD4691 (16-ch, 500 kSPS),
> AD4692 (16-ch, 1 MSPS), AD4693 (8-ch, 500 kSPS) and
> AD4694 (8-ch, 1 MSPS).
>
> The driver implements a custom regmap layer over raw SPI to handle the
> device's mixed 1/2/3/4-byte register widths and uses the standard IIO
> read_raw/write_raw interface for single-channel reads.
>
> The chip idles in Autonomous Mode so that single-shot read_raw can use
> the internal oscillator without disturbing the hardware configuration.
>
> Three voltage supply domains are managed: avdd (required), vio, and a
> reference supply on either the REF pin (ref-supply, external buffer)
> or the REFIN pin (refin-supply, uses the on-chip reference buffer;
> REFBUF_EN is set accordingly). Hardware reset is performed via
> the reset controller framework; a software reset through SPI_CONFIG_A
> is used as fallback when no hardware reset is available.
>
> Accumulator channel masking for single-shot reads uses ACC_MASK_REG via
> an ADDR_DESCENDING SPI write, which covers both mask bytes in a single
> 16-bit transfer.
>
> Reviewed-by: David Lechner <dlechner@baylibre.com>
> Signed-off-by: Radu Sabau <radu.sabau@analog.com>
Hi Radu

Just one query that Sashiko raised that made me look
closer at how you are handling different register sizes.
https://sashiko.dev/#/patchset/20260430-ad4692-multichannel-sar-adc-driver-v9-0-33e439e4fb87%40analog.com

There was also a question about whether the sampling frequency control would
be better described as shared by all.

> diff --git a/drivers/iio/adc/ad4691.c b/drivers/iio/adc/ad4691.c
> new file mode 100644
> index 000000000000..05826b762c7f
> --- /dev/null
> +++ b/drivers/iio/adc/ad4691.c

> +static int ad4691_reg_read(void *context, unsigned int reg, unsigned int *val)
> +{
> + struct spi_device *spi = context;
> + u8 tx[2], rx[4];
> + int ret;
> +
> + /* Set bit 15 to mark the operation as READ. */
> + put_unaligned_be16(0x8000 | reg, tx);
> +
> + switch (reg) {
> + case 0 ... AD4691_OSC_FREQ_REG:
> + case AD4691_SPARE_CONTROL ... AD4691_ACC_SAT_OVR_REG(15):

Sashiko raised a query here.
"Will this result in a truncated 1-byte read for AD4691_ACC_MASK_REG (0x185)?
AD4691_ACC_MASK_REG falls into the range between AD4691_SPARE_CONTROL and
AD4691_ACC_SAT_OVR_REG(15). In ad4691_reg_write(), AD4691_ACC_MASK_REG is
handled explicitly alongside AD4691_STD_SEQ_CONFIG to perform a 16-bit
write, but it seems missing from the 2-byte read block here."

Just to check - the reasoning behind not just treating these as
fixed sized registers and using bulk reads and writes is the statement
about them being invalid if partially written?

The ACK_MASK_REG is documented as two separate 8 bit registers so why
attempt to treat it as a larger one?

> + ret = spi_write_then_read(spi, tx, sizeof(tx), rx, 1);
> + if (ret)
> + return ret;
> + *val = rx[0];
> + return 0;
> + case AD4691_STD_SEQ_CONFIG:
> + case AD4691_AVG_IN(0) ... AD4691_AVG_IN(15):
> + ret = spi_write_then_read(spi, tx, sizeof(tx), rx, 2);
> + if (ret)
> + return ret;
> + *val = get_unaligned_be16(rx);
> + return 0;
> + case AD4691_AVG_STS_IN(0) ... AD4691_AVG_STS_IN(15):
> + case AD4691_ACC_IN(0) ... AD4691_ACC_IN(15):
> + ret = spi_write_then_read(spi, tx, sizeof(tx), rx, 3);
> + if (ret)
> + return ret;
> + *val = get_unaligned_be24(rx);
> + return 0;
> + case AD4691_ACC_STS_DATA(0) ... AD4691_ACC_STS_DATA(15):
> + ret = spi_write_then_read(spi, tx, sizeof(tx), rx, 4);
> + if (ret)
> + return ret;
> + *val = get_unaligned_be32(rx);
> + return 0;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +static int ad4691_reg_write(void *context, unsigned int reg, unsigned int val)
> +{
> + struct spi_device *spi = context;
> + u8 tx[4];
> +
> + put_unaligned_be16(reg, tx);
> +
> + switch (reg) {
> + case 0 ... AD4691_OSC_FREQ_REG:
> + case AD4691_SPARE_CONTROL ... AD4691_ACC_MASK_REG - 1:
> + case AD4691_ACC_MASK_REG + 1 ... AD4691_GPIO_MODE2_REG:
> + if (val > U8_MAX)
> + return -EINVAL;
> + tx[2] = val;
> + return spi_write_then_read(spi, tx, 3, NULL, 0);
> + case AD4691_ACC_MASK_REG:
> + case AD4691_STD_SEQ_CONFIG:
> + if (val > U16_MAX)
> + return -EINVAL;
> + put_unaligned_be16(val, &tx[2]);
> + return spi_write_then_read(spi, tx, 4, NULL, 0);
> + default:
> + return -EINVAL;
> + }
> +}