Re: [PATCH] iio: adc: ad7606: remove frstdata check

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 17 Apr 2024 09:11:18 +0000
Guillaume Stols <gstols@baylibre.com> wrote:

> Frstdata pin is set high during the first sample's transmission and
> then set low.
> This code chunk attempts to recover from an eventual glitch in the clock
> by checking frstdata state after reading the first channel's sample.
> Currently, in serial mode, this check happens AFTER the 16th pulse, and if
> frstdata is not set it resets the device and returns EINVAL.
> According to the datasheet, "The FRSTDATA output returns to a logic low
> following the 16th SCLK falling edge.", thus after the 16th pulse, the check
> will always be true, and the driver will not work as expected.
> Even if it was working, the usefulness of this check is limited, since
> it would only detect a glitch on the first channel, but not on the
> following ones, and the convst pulse will reset the communication sequence at
> each new conversion.
> 
> Signed-off-by: Guillaume Stols <gstols@baylibre.com>

Michael, I'm sure you remember this well - it was only 13 years ago you wrote
this...

https://lore.kernel.org/all/1296744691-24320-1-git-send-email-michael.hennerich@analog.com/

Anyhow, I'd like an Ack or a statement of you have no idea any more and i should
go with what Guillaume has worked out...

Jonathan

> ---
> This is the first commit of cleanup series. It will be followed by more
> cleanups and support for more parts and features.

Sounds good.

> ---
>  drivers/iio/adc/ad7606.c | 30 ------------------------------
>  drivers/iio/adc/ad7606.h |  3 ---
>  2 files changed, 33 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7606.c b/drivers/iio/adc/ad7606.c
> index 1928d9ae5bcf..f85eb0832703 100644
> --- a/drivers/iio/adc/ad7606.c
> +++ b/drivers/iio/adc/ad7606.c
> @@ -88,31 +88,6 @@ static int ad7606_read_samples(struct ad7606_state *st)
>  {
>  	unsigned int num = st->chip_info->num_channels - 1;
>  	u16 *data = st->data;
> -	int ret;
> -
> -	/*
> -	 * The frstdata signal is set to high while and after reading the sample
> -	 * of the first channel and low for all other channels. This can be used
> -	 * to check that the incoming data is correctly aligned. During normal
> -	 * operation the data should never become unaligned, but some glitch or
> -	 * electrostatic discharge might cause an extra read or clock cycle.
> -	 * Monitoring the frstdata signal allows to recover from such failure
> -	 * situations.
> -	 */
> -
> -	if (st->gpio_frstdata) {
> -		ret = st->bops->read_block(st->dev, 1, data);
> -		if (ret)
> -			return ret;
> -
> -		if (!gpiod_get_value(st->gpio_frstdata)) {
> -			ad7606_reset(st);
> -			return -EIO;
> -		}
> -
> -		data++;
> -		num--;
> -	}
>  
>  	return st->bops->read_block(st->dev, num, data);
>  }
> @@ -450,11 +425,6 @@ static int ad7606_request_gpios(struct ad7606_state *st)
>  	if (IS_ERR(st->gpio_standby))
>  		return PTR_ERR(st->gpio_standby);
>  
> -	st->gpio_frstdata = devm_gpiod_get_optional(dev, "adi,first-data",
> -						    GPIOD_IN);
> -	if (IS_ERR(st->gpio_frstdata))
> -		return PTR_ERR(st->gpio_frstdata);
> -
>  	if (!st->chip_info->oversampling_num)
>  		return 0;
>  
> diff --git a/drivers/iio/adc/ad7606.h b/drivers/iio/adc/ad7606.h
> index 0c6a88cc4695..eacb061de6f8 100644
> --- a/drivers/iio/adc/ad7606.h
> +++ b/drivers/iio/adc/ad7606.h
> @@ -80,8 +80,6 @@ struct ad7606_chip_info {
>   * @gpio_range		GPIO descriptor for range selection
>   * @gpio_standby	GPIO descriptor for stand-by signal (STBY),
>   *			controls power-down mode of device
> - * @gpio_frstdata	GPIO descriptor for reading from device when data
> - *			is being read on the first channel
>   * @gpio_os		GPIO descriptors to control oversampling on the device
>   * @complete		completion to indicate end of conversion
>   * @trig		The IIO trigger associated with the device.
> @@ -108,7 +106,6 @@ struct ad7606_state {
>  	struct gpio_desc		*gpio_reset;
>  	struct gpio_desc		*gpio_range;
>  	struct gpio_desc		*gpio_standby;
> -	struct gpio_desc		*gpio_frstdata;
>  	struct gpio_descs		*gpio_os;
>  	struct iio_trigger		*trig;
>  	struct completion		completion;
> 
> ---
> base-commit: 62d3fb9dcc091ccdf25eb3b716e90e07e3ed861f
> change-id: 20240416-cleanup-ad7606-161e2ed9818b
> 
> Best regards,