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

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Message-ID: <20250518175832.77b8d670@jic23-huawei>
Date: Sun, 18 May 2025 17:58:32 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Andy Shevchenko <andy@...nel.org>
Cc: 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, jonath4nns@...il.com, dlechner@...libre.com
Subject: Re: [PATCH v8 08/11] iio: adc: ad7768-1: add support for
 Synchronization over SPI

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?


> > +	/* 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;
> > +}  
>