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

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Thu, 29 May 2025 19:50:29 -0300
Jonathan Santos <Jonathan.Santos@analog.com> 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.
> 
> Reviewed-by: David Lechner <dlechner@baylibre.com>
> Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>

A couple of trivial comments.  Not enough to respin unless something else comes
up.


> @@ -296,6 +301,27 @@ static const struct regmap_config ad7768_regmap24_config = {
>  	.max_register = AD7768_REG24_COEFF_DATA,
>  };
>  
> +static int ad7768_send_sync_pulse(struct ad7768_state *st)
> +{
> +	if (st->en_spi_sync)
> +		return regmap_write(st->regmap, AD7768_REG_SYNC_RESET, 0x00);
> +
> +	/*
> +	 * The datasheet specifies a minimum SYNC_IN pulse width of 1.5 × Tmclk,
> +	 * where Tmclk is the MCLK period. The supported MCLK frequencies range
> +	 * from 0.6 MHz to 17 MHz, which corresponds to a minimum SYNC_IN pulse
> +	 * width of approximately 2.5 µs in the worst-case scenario (0.6 MHz).
> +	 *
> +	 * Add a delay to ensure the pulse width is always sufficient to
> +	 * trigger synchronization.
> +	 */
> +	gpiod_set_value_cansleep(st->gpio_sync_in, 1);
> +	fsleep(3);
> +	gpiod_set_value_cansleep(st->gpio_sync_in, 0);

This change + comment should really have been in a separate patch
as there is always the potential someone might want to backport it.

> +
> +	return 0;
> +}
> +
>  static int ad7768_set_mode(struct ad7768_state *st,
>  			   enum ad7768_conv_mode mode)
>  {
> @@ -392,10 +418,7 @@ static int ad7768_set_dig_fil(struct ad7768_state *st,
>  		return ret;
>  
>  	/* A sync-in pulse is required every time the filter dec rate changes */
> -	gpiod_set_value(st->gpio_sync_in, 1);
> -	gpiod_set_value(st->gpio_sync_in, 0);
> -
> -	return 0;
> +	return ad7768_send_sync_pulse(st);
>  }

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

Really trivial but if you respin for some reason blank line here.

> +	return 0;
> +}