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

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Message-ID: <aPIqCrvaPQZg7Lo8@debian-BULLSEYE-live-builder-AMD64>
Date: Fri, 17 Oct 2025 08:35:38 -0300
From: Marcelo Schmitt <marcelo.schmitt1@...il.com>
To: David Lechner <dlechner@...libre.com>
Cc: 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, 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,
	Trevor Gamblin <tgamblin@...libre.com>,
	Axel Haslam <ahaslam@...libre.com>
Subject: Re: [PATCH v5 5/7] iio: adc: ad4030: Add SPI offload support

On 10/16, David Lechner wrote:
> 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.
> 
I had coded that in a way I think would work for the dual channel devices, but
it didn't really work for single-channel adaq4216. And yes, if anyone asks
for offload with common-mode data, we shall probably be able to it that later.


> > - 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.

Ack.
> 
> > +		 * 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>
> 
Thanks,
Marcelo