linux-kernel - Re: [PATCH v10 09/12] iio: adc: ad7768-1: add support for Synchronization over SPI

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Message-ID: <aEE0xiCp1IIt9c0M@smile.fi.intel.com>
Date: Thu, 5 Jun 2025 09:10:14 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Jonathan Santos <Jonathan.Santos@...log.com>
Cc: 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, jic23@...nel.org, 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 v10 09/12] iio: adc: ad7768-1: add support for
 Synchronization over SPI

On Wed, Jun 04, 2025 at 04:37:09PM -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.

...

> +static int ad7768_trigger_sources_sync_setup(struct device *dev,
> +					     struct fwnode_handle *fwnode,
> +					     struct ad7768_state *st)
> +{
> +	struct fwnode_reference_args args;
> +	struct fwnode_handle *ref __free(fwnode_handle) = NULL;
> +	int ret;
> +
> +	ret = fwnode_property_get_reference_args(fwnode, "trigger-sources",
> +						 "#trigger-source-cells", 0,
> +						 AD7768_TRIGGER_SOURCE_SYNC_IDX, &args);
> +	if (ret)
> +		return ret;
> +
> +	ref = args.fwnode;
> +	/* First, try getting the GPIO trigger source */
> +	if (fwnode_device_is_compatible(ref, "gpio-trigger")) {

> +		st->gpio_sync_in = devm_fwnode_gpiod_get_index(dev, ref, NULL,
> +							       0,

This 0 is close to NULL semantically, please move it to the above line to make
the split more logical.

> +							       GPIOD_OUT_LOW,
> +							       "sync-in");
> +		return PTR_ERR_OR_ZERO(st->gpio_sync_in);
> +	}
> +
> +	/*
> +	 * 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.
> +	 */
> +	return dev_err_probe(dev, -EOPNOTSUPP, "Invalid synchronization trigger source\n");
> +}

-- 
With Best Regards,
Andy Shevchenko