linux-kernel - Re: [PATCH v7 08/12] iio: adc: ad7768-1: add multiple scan types to support 16-bits mode

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Message-ID: <21b0e8e3-f9ca-4fa4-ba24-233d2e96944e@baylibre.com>
Date: Thu, 8 May 2025 13:01:49 -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,
 David Lechner <dlechner@...lire.com>
Subject: Re: [PATCH v7 08/12] iio: adc: ad7768-1: add multiple scan types to
 support 16-bits mode

On 5/8/25 12:04 PM, Jonathan Santos wrote:
> When the device is configured to decimation x8, only possible in the
> sinc5 filter, output data is reduced to 16-bits in order to support
> 1 MHz of sampling frequency due to clock limitation.
> 
> Use multiple scan types feature to enable the driver to switch
> scan type at runtime, making it possible to support both 24-bit and
> 16-bit resolution.
> 
> Reviewed-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> Reviewed-by: David Lechner <dlechner@...lire.com>
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---
> v7 Changes:
> * Added TODO comment to use spi_bpw_to_bytes() helper function.
> * Minor commit description changes.
> 

...

> @@ -675,9 +723,16 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
>  	struct iio_poll_func *pf = p;
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct ad7768_state *st = iio_priv(indio_dev);
> +	const struct iio_scan_type *scan_type;
>  	int ret;
>  
> -	ret = spi_read(st->spi, &st->data.scan.chan, 3);
> +	scan_type = iio_get_current_scan_type(indio_dev, &indio_dev->channels[0]);
> +	if (IS_ERR(scan_type))
> +		goto out;
> +
> +	/* TODO: Use spi_bpw_to_bytes() helper function. */

spi_bpw_to_bytes() is to get buffer size when setting bits_per_word. It doesn't
apply to spi_read(). So we should drop this comment.

> +	ret = spi_read(st->spi, &st->data.scan.chan,
> +		       BITS_TO_BYTES(scan_type->realbits));

If we replaced BITS_TO_BYTES() with spi_bpw_to_bytes(), then it would read 4
bytes instead of 3 when realbits == 24, which isn't what we want.

>  	if (ret < 0)
>  		goto out;
>