Re: [PATCH 5/6] gpio: ad7768: Add AD7768 GPIO auxiliary driver

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Configuring GPIO direction to output before setting the intended output value causes a transient hardware glitch.
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--- Patch [5]: [PATCH 5/6] gpio: ad7768: Add AD7768 GPIO auxiliary driver ---
commit 0fd38c3af385be1ae0dc21601c951d0e8f32ade5
Author: Janani Sunil <janani.sunil@analog.com>

gpio: ad7768: Add AD7768 GPIO auxiliary driver

This commit adds an auxiliary bus driver to expose 5 general-purpose I/O
pins on the AD7768/AD7768-4 ADC as a GPIO controller. The driver handles pin
direction and value configuration by sharing a regmap with the parent IIO
device.

> diff --git a/drivers/gpio/gpio-ad7768.c b/drivers/gpio/gpio-ad7768.c
> new file mode 100644
> index 0000000000000..c2f01b1abd7c9
> --- /dev/null
> +++ b/drivers/gpio/gpio-ad7768.c

[ ... ]

> +static int ad7768_gpio_direction_output(struct gpio_chip *chip,
> +					unsigned int offset, int value)
> +{
> +	struct ad7768_gpio_state *st = gpiochip_get_data(chip);
> +	int ret;
> +
> +	PM_RUNTIME_ACQUIRE_IF_ENABLED_AUTOSUSPEND(st->parent, pm);
> +	ret = PM_RUNTIME_ACQUIRE_ERR(&pm);
> +	if (ret)
> +		return ret;
> +
> +	guard(mutex)(&st->lock);
> +
> +	ret = regmap_update_bits(st->regmap, AD7768_REG_GPIO_CONTROL,
> +				 BIT(offset), AD7768_GPIO_OUTPUT(offset));
> +	if (ret)
> +		return ret;
> +
> +	return regmap_update_bits(st->regmap, AD7768_REG_GPIO_WRITE,
> +				  BIT(offset), value << offset);

[Severity: Medium]
Will this sequence cause a transient hardware glitch on the GPIO pin?

By configuring the pin direction to output in AD7768_REG_GPIO_CONTROL before
setting the intended output value in AD7768_REG_GPIO_WRITE, the hardware
could briefly drive the line with whatever stale value is currently held in
the write register.

Would it be safer to write the intended value to AD7768_REG_GPIO_WRITE first,
and only then switch the pin direction to output?

> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260709-ad7768-driver-v1-0-44e1194fd96a@analog.com?part=5