linux-kernel - Re: [PATCH v8 08/11] iio: adc: ad7768-1: add support for Synchronization over SPI

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Message-ID: <aDEMEWQvu0r9stCh@JSANTO12-L01.ad.analog.com>
Date: Fri, 23 May 2025 21:00:17 -0300
From: Jonathan Santos <jonath4nns@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Andy Shevchenko <andy@...nel.org>,
	Jonathan Santos <Jonathan.Santos@...log.com>,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
	nuno.sa@...log.com, Michael.Hennerich@...log.com,
	marcelo.schmitt@...log.com, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, marcelo.schmitt1@...il.com,
	linus.walleij@...aro.org, brgl@...ev.pl, lgirdwood@...il.com,
	broonie@...nel.org, dlechner@...libre.com
Subject: Re: [PATCH v8 08/11] iio: adc: ad7768-1: add support for
 Synchronization over SPI

On 05/18, Jonathan Cameron wrote:
> On Fri, 16 May 2025 12:29:02 +0300
> Andy Shevchenko <andy@...nel.org> wrote:
> 
> > On Thu, May 15, 2025 at 06:13:56PM -0300, Jonathan Santos wrote:
> > > The synchronization method using GPIO requires the generated pulse to be
> > > truly synchronous with the base MCLK signal. When it is not possible to
> > > do that in hardware, the datasheet recommends using synchronization over
> > > SPI, where the generated pulse is already synchronous with MCLK. This
> > > requires the SYNC_OUT pin to be connected to the SYNC_IN pin.
> > > 
> > > Use trigger-sources property to enable device synchronization over SPI
> > > and multi-device synchronization while replacing sync-in-gpios property.  
> Given some discussion in here I'll not (yet) pick up this series.
> 
> It's almost certainly just missed the coming merge window anyway so
> we have time.
> 
> > 
> > ...
> > 
> > > +static int ad7768_trigger_sources_get_sync(struct device *dev,
> > > +					   struct ad7768_state *st)
> > > +{
> > > +	struct fwnode_reference_args args;
> > > +	struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > +	int ret;
> > > +
> > > +	/*
> > > +	 * The AD7768-1 allows two primary methods for driving the SYNC_IN pin
> > > +	 * to synchronize one or more devices:
> > > +	 * 1. Using an external GPIO.
> > > +	 * 2. Using a SPI command, where the SYNC_OUT pin generates a
> > > +	 *    synchronization pulse that drives the SYNC_IN pin.
> > > +	 */
> > > +	if (!fwnode_property_present(fwnode, "trigger-sources")) {  
> > 
> > I'm wondering if you can split the below to a separate function and do something like
> > 
> > 	if (fwnode_property_present(...))
> > 		return setup_trigger_source(...);
> > 
> > 	...
> > 	en_spi_sync = true;
> > 	return 0;
> > 
> > > +		/*
> > > +		 * In the absence of trigger-sources property, enable self
> > > +		 * synchronization over SPI (SYNC_OUT).
> > > +		 */
> > > +		st->en_spi_sync = true;
> > > +		return 0;
> > > +	}
> > > +
> > > +	ret = fwnode_property_get_reference_args(fwnode,
> > > +						 "trigger-sources",
> > > +						 "#trigger-source-cells",
> > > +						 0,
> > > +						 AD7768_TRIGGER_SOURCE_SYNC_IDX,
> > > +						 &args);  
> > 
> > 
> > __free(fwnode_handle) ?
> 
> For args.fwnode?
> 
> That's fiddly to do and needs a different local variable to...
> 
> 
> 
> > 
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	fwnode = args.fwnode;
> 
> this one.
> 
> You could wrap it up in a function to make that works cleanly.
> So something similar to fwnode_find_reference() but with the
> rest of the arguments.  Is there appetite for such a wrapper
> in the generic property code?
>

you mean like:

fwnode_find_reference_args(const struct fwnode_handle *fwnode,
			   const char *name, const char *nargs_prop,
			   unsigned int nargs, unsigned int index,
			   struct fwnode_reference_args *args)

I don't know if it helps that much and since we are not handling
arguments right know, I think fwnode_find_reference() would work (or not?).
In that case maybe we add some note or TODO to explain why. 

> 
> > > +	/* First, try getting the GPIO trigger source */
> > > +	if (fwnode_device_is_compatible(fwnode, "gpio-trigger")) {
> > > +		st->gpio_sync_in = devm_fwnode_gpiod_get_index(dev, fwnode,
> > > +							       NULL,
> > > +							       0,
> > > +							       GPIOD_OUT_LOW,
> > > +							       "sync-in");
> > > +		ret = PTR_ERR_OR_ZERO(st->gpio_sync_in);
> > > +		goto out_put_node;
> > > +	}
> > > +
> > > +	/*
> > > +	 * TODO: Support the other cases when we have a trigger subsystem to
> > > +	 * reliably handle other types of devices as trigger sources.
> > > +	 *
> > > +	 * For now, return an error message. For self triggering, omit the
> > > +	 * trigger-sources property.
> > > +	 */
> > > +	ret = dev_err_probe(dev, -EOPNOTSUPP, "Invalid synchronization trigger source\n");
> > > +
> > > +out_put_node:  
> > 
> > The above will allow to get rid of this label.
> > 
> > > +	fwnode_handle_put(args.fwnode);
> > > +	return ret;
> > > +}  
> > 
>