linux-kernel - Re: [PATCH v10 01/12] iio: adc: ad7768-1: Ensure SYNC

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Message-ID: <57edc6dc-bbf7-4491-a43b-c33b9466d8d0@baylibre.com>
Date: Wed, 4 Jun 2025 15:14:59 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org
Cc: andy@...nel.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
Subject: Re: [PATCH v10 01/12] iio: adc: ad7768-1: Ensure SYNC_IN pulse
 minimum timing requirement

On 6/4/25 2:35 PM, Jonathan Santos wrote:
> The SYNC_IN pulse width must be at least 1.5 x Tmclk, corresponding to
> ~2.5 µs at the lowest supported MCLK frequency. Add a 3 µs delay to
> ensure reliable synchronization timing even for the worst-case scenario.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---

Reviewed-by: David Lechner <dlechner@...libre.com>

> v10 Changes:
> * New patch.
> ---
>  drivers/iio/adc/ad7768-1.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> index 51134023534a..8b414a102864 100644
> --- a/drivers/iio/adc/ad7768-1.c
> +++ b/drivers/iio/adc/ad7768-1.c
> @@ -252,6 +252,24 @@ static const struct regmap_config ad7768_regmap24_config = {
>  	.max_register = AD7768_REG24_COEFF_DATA,
>  };
>  
> +static int ad7768_send_sync_pulse(struct ad7768_state *st)
> +{
> +	/*
> +	 * 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);
> +
> +	return 0;

There is no other return, so this could be a void function. In this case, it is
fine because a later patch adds another return. But in the future, be sure to
mention that in the commit message (or below the ---) so that reviewers will
know why without having to look ahead.

> +}
> +