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

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Message-ID: <a5cc1d4850b17569900124e1e4cf7549cedc7692.camel@gmail.com>
Date: Sat, 18 Oct 2025 15:16:57 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.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,
 dlechner@...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 16:54 -0300, Marcelo Schmitt wrote:
> On 10/17, Nuno Sá wrote:
> > On Tue, 2025-10-14 at 19:22 -0300, 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>
> > > ---
> > 
> ...
> > > +static int ad4030_offload_buffer_postenable(struct iio_dev *indio_dev)
> > > +{
> > > +	struct ad4030_state *st = iio_priv(indio_dev);
> > > +	unsigned int reg_modes;
> > > +	int ret, ret2;
> > > +
> ...
> > > +	ret = spi_offload_trigger_enable(st->offload, st-
> > > >offload_trigger,
> > > +					 &st->offload_trigger_config);
> > > +	if (ret)
> > > +		goto out_pwm_disable;
> > > +
> > > +	return 0;
> > > +
> > > +out_pwm_disable:
> > > +	pwm_disable(st->cnv_trigger);
> > > +out_unoptimize:
> > > +	spi_unoptimize_message(&st->offload_msg);
> > > +out_reset_mode:
> > > +	/* reenter register configuration mode */
> > > +	ret2 = ad4030_enter_config_mode(st);
> > 
> > nit: if ret2 is not being used at all, maybe just
> ret2 is logged on the error message below so I guess I'll keep it as it is.
> > 
> > if (ad4030_enter_config_mode(st))
> > 	
> > > +	if (ret2)
> > > +		dev_err(&st->spi->dev,
> > > +			"couldn't reenter register configuration mode:
> > > %d\n",
> > > +			ret2);
> here we log the error code. We only reach it if reg access fails after
> something on offload buffer enable have failed first. We cannot reuse ret here
> because we would be shadowing the original error code.

Right :facepalm: