linux-kernel - Re: [PATCH v9 09/12] iio: adc: ad7768-1: add support for Synchronization over SPI

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Message-ID: <aDnuvAdkcTAP2tMt@smile.fi.intel.com>
Date: Fri, 30 May 2025 20:45:32 +0300
From: Andy Shevchenko <andy@...nel.org>
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,
	linux-acpi@...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,
	rafael@...nel.org, djrscally@...il.com
Subject: Re: [PATCH v9 09/12] iio: adc: ad7768-1: add support for
 Synchronization over SPI

On Thu, May 29, 2025 at 07:50:29PM -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.

...

> struct ad7768_state {

>  	struct iio_trigger *trig;
>  	struct gpio_desc *gpio_sync_in;
>  	struct gpio_desc *gpio_reset;

> +	bool en_spi_sync;

I'm wondering if moving this...

>  	const char *labels[ARRAY_SIZE(ad7768_channels)];
>  	struct gpio_chip gpiochip;

...to here saves a few bytes in accordance to `pahole`.

>  };

...

> +static int ad7768_trigger_sources_sync_setup(struct device *dev,
> +					     struct fwnode_handle *dev_fwnode,
> +					     struct ad7768_state *st)
> +{
> +	struct fwnode_reference_args args;
> +
> +	struct fwnode_handle *fwnode __free(fwnode_handle) =
> +		fwnode_find_reference_args(dev_fwnode, "trigger-sources",
> +					   "#trigger-source-cells", 0,
> +					   AD7768_TRIGGER_SOURCE_SYNC_IDX, &args);

I don't see how args are being used. This puts in doubt the need of the first
patch.

> +	if (IS_ERR(fwnode))
> +		return PTR_ERR(fwnode);
> +
> +	/* 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");
> +		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");
> +}

...

> +static int ad7768_trigger_sources_get_sync(struct device *dev,
> +					   struct ad7768_state *st)
> +{
> +	struct fwnode_handle *dev_fwnode = dev_fwnode(dev);

Call it just fwnode.

> +	/*
> +	 * 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(dev_fwnode, "trigger-sources"))
> +		return ad7768_trigger_sources_sync_setup(dev, dev_fwnode, st);
> +
> +	/*
> +	 * In the absence of trigger-sources property, enable self
> +	 * synchronization over SPI (SYNC_OUT).
> +	 */
> +	st->en_spi_sync = true;
> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko