On Tue, 7 Jan 2025 17:50:29 -0600
David Lechner [off-list ref] wrote:

On 1/7/25 9:27 AM, Jonathan Santos wrote:

quoted

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 SYNC_IN pin.

Add the option to handle device synchronization over SPI.

Signed-off-by: Jonathan Santos <redacted>
---  

...

quoted

 static int ad7768_gpio_direction_input(struct gpio_chip *chip, unsigned int offset)

@@ -697,11 +708,21 @@ static int ad7768_setup(struct ad7768_state *st)
 	if (ret)
 		return ret;
 
-	st->gpio_sync_in = devm_gpiod_get(&st->spi->dev, "adi,sync-in",
-					  GPIOD_OUT_LOW);
+	st->gpio_sync_in = devm_gpiod_get_optional(&st->spi->dev, "adi,sync-in",
+						   GPIOD_OUT_LOW);
 	if (IS_ERR(st->gpio_sync_in))
 		return PTR_ERR(st->gpio_sync_in);
 
+	if (device_property_present(&st->spi->dev, "adi,sync-in-spi"))
+		st->en_spi_sync = true;
+
+	/*
+	 * GPIO and SPI Synchronization are mutually exclusive.
+	 * Return error if both are enabled  

Should it also be an error if we have neither? Otherwise it sounds like
decimation won't work correctly since there is a comment that says we have
to toggle this after updating the decimation rate register.

I'm not quite sure how this interacts with potential future support
for daisy chaining but for now, if we have no GPIO specified why can't
we assume spi sync is the way to go?

If no GPIO is provided and for a single device SYNC_OUT is not wired
to SYNC_IN I think the board is broken anyway and we don't have to care.

Jonathan

quoted

+	 */
+	if (st->gpio_sync_in && st->en_spi_sync)
+		return -EINVAL;  

A dev_err_probe() message would be helpful here when creating a new DT and
bringing up a new system since it is easy to forget a property or make a typo
that could lead to this error.

quoted

+
 	ret = ad7768_gpio_init(st);
 	if (ret < 0)
 		return ret;