On Thu, 29 May 2025 19:50:29 -0300
Jonathan Santos <Jonathan.Santos@xxxxxxxxxx> 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@xxxxxxxxxxxx>
> Signed-off-by: Jonathan Santos <Jonathan.Santos@xxxxxxxxxx>
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;
> +}
