linux-kernel - Re: [PATCH v5 5/7] iio: adc: ad4030: Add SPI offload support

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Message-ID: <e677f27a-787a-433c-8516-99ff1d33f2c6@baylibre.com>
Date: Thu, 16 Oct 2025 11:40:00 -0500
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: jic23@...nel.org, michael.hennerich@...log.com, nuno.sa@...log.com,
 eblanc@...libre.com, andy@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, corbet@....net, marcelo.schmitt1@...il.com,
 Trevor Gamblin <tgamblin@...libre.com>, Axel Haslam <ahaslam@...libre.com>
Subject: Re: [PATCH v5 5/7] iio: adc: ad4030: Add SPI offload support

On 10/14/25 5:22 PM, Marcelo Schmitt wrote:
> AD4030 and similar ADCs can capture data at sample rates up to 2 mega
> samples per second (MSPS). Not all SPI controllers are able to achieve such
> high throughputs and even when the controller is fast enough to run
> transfers at the required speed, it may be costly to the CPU to handle
> transfer data at such high sample rates. Add SPI offload support for AD4030
> and similar ADCs to enable data capture at maximum sample rates.
> 
> Co-developed-by: Trevor Gamblin <tgamblin@...libre.com>
> Signed-off-by: Trevor Gamblin <tgamblin@...libre.com>
> Co-developed-by: Axel Haslam <ahaslam@...libre.com>
> Signed-off-by: Axel Haslam <ahaslam@...libre.com>
> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> ---
> Change log v4 -> v5
> - Made Kconfig entry depend on PWM and select other features.
> - Reused ad4030_exit_config_mode() in ad4030_offload_buffer_postenable().
> - Dropped common-mode voltage support on SPI offload setup.

Curious why you chose this. I guess it will be fine to add it later
if anyone ever actually needs it.

> - Adjusted offload trigger period calculation.
> - No longer setting data frame mode from ad4030_set_avg_frame_len().
> - Rearranged code to reduce patch diff.
> 
>  drivers/iio/adc/Kconfig  |   5 +
>  drivers/iio/adc/ad4030.c | 425 +++++++++++++++++++++++++++++++++++++--
>  2 files changed, 416 insertions(+), 14 deletions(-)
> 

...

> @@ -512,11 +643,30 @@ static int ad4030_set_avg_frame_len(struct iio_dev *dev, int avg_val)
>  	struct ad4030_state *st = iio_priv(dev);
>  	unsigned int avg_log2 = ilog2(avg_val);
>  	unsigned int last_avg_idx = ARRAY_SIZE(ad4030_average_modes) - 1;
> +	int freq_hz;
>  	int ret;
>  
>  	if (avg_val < 0 || avg_val > ad4030_average_modes[last_avg_idx])
>  		return -EINVAL;
>  
> +	if (st->offload_trigger) {
> +		/*
> +		 * The sample averaging and sampling frequency configurations
> +		 * are mutually dependent one from another. That's because the

s/one from another/on each other/

"one from another" makes it sound like they are independent rather than
dependent.

> +		 * effective data sample rate is fCNV / 2^N, where N is the
> +		 * number of samples being averaged.
> +		 *
> +		 * When SPI offload is supported and we have control over the
> +		 * sample rate, the conversion start signal (CNV) and the SPI
> +		 * offload trigger frequencies must be re-evaluated so data is
> +		 * fetched only after 'avg_val' conversions.
> +		 */
> +		ad4030_get_sampling_freq(st, &freq_hz);
> +		ret = ad4030_update_conversion_rate(st, freq_hz, avg_log2);
> +		if (ret)
> +			return ret;
> +	}
> +
LGTM.

Reviewed-by: David Lechner <dlechner@...libre.com>