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

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Message-ID: <d56b48901843a7a3f7e6543e46eadb3901f58bfe.camel@gmail.com>
Date: Fri, 17 Oct 2025 16:03:42 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>, 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 Fri, 2025-10-17 at 08:35 -0300, Marcelo Schmitt wrote:
> 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.

I guess that if someone really wants it, the data will still be available in the
sample. But yes, it would be nice to properly support it at some point.

- Nuno Sá