Re: [PATCH v5 4/4] iio: adc: ad9467: check for backend capabilities

["Nuno Sá" <noname.nuno@gmail.com>]

On Fri, 2026-01-30 at 09:17 +0000, Tomas Melin wrote:
> Add capability checks for operation with backends that do not necessarily
> support full set of features, but are otherwise compatible with the device.
> This ensures a fully functional device, but with limited capabilities.
> 
> Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
> ---
>  drivers/iio/adc/ad9467.c | 69 ++++++++++++++++++++++++++++++------------------
>  1 file changed, 43 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
> index 59c3fa3bcc9b..d768f7bf2a1c 100644
> --- a/drivers/iio/adc/ad9467.c
> +++ b/drivers/iio/adc/ad9467.c
> @@ -913,7 +913,9 @@ static int __ad9467_update_clock(struct ad9467_state *st, long r_clk)
>  		return ret;
>  
>  	guard(mutex)(&st->lock);
> -	return ad9467_calibrate(st);
> +	if (iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION))
> +		return ad9467_calibrate(st);
> +	return 0;
>  }
>  
>  static int ad9467_write_raw(struct iio_dev *indio_dev,
> @@ -1119,12 +1121,15 @@ static ssize_t ad9467_chan_test_mode_read(struct file *file,
>  		len = scnprintf(buf, sizeof(buf), "Running \"%s\" Test:\n\t",
>  				ad9467_test_modes[chan->mode]);
>  
> -		ret = iio_backend_debugfs_print_chan_status(st->back, chan->idx,
> -							    buf + len,
> -							    sizeof(buf) - len);
> -		if (ret < 0)
> -			return ret;
> -		len += ret;
> +		if (iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION)) {
> +			ret = iio_backend_debugfs_print_chan_status(st->back,
> +								    chan->idx,
> +								    buf + len,
> +								    sizeof(buf) - len);
> +			if (ret < 0)
> +				return ret;
> +			len += ret;

Given that we can't really check the status we could maybe do this in a better way. See
below...
> +		}
>  	} else if (chan->mode == AN877_ADC_TESTMODE_OFF) {
>  		len = scnprintf(buf, sizeof(buf), "No test Running...\n");
>  	} else {
> @@ -1188,16 +1193,19 @@ static ssize_t ad9467_chan_test_mode_write(struct file *file,
>  			return ret;
>  
>  		/*  some patterns have a backend matching monitoring block */
> -		if (mode == AN877_ADC_TESTMODE_PN9_SEQ) {
> -			ret = ad9467_backend_testmode_on(st, chan->idx,
> +		if (iio_backend_has_caps(st->back,
> +					 IIO_BACKEND_CAP_CALIBRATION)) {
> +			if (mode == AN877_ADC_TESTMODE_PN9_SEQ) {
> +				ret = ad9467_backend_testmode_on(st, chan->idx,
>  							 IIO_BACKEND_ADI_PRBS_9A);
> -			if (ret)
> -				return ret;
> -		} else if (mode == AN877_ADC_TESTMODE_PN23_SEQ) {
> -			ret = ad9467_backend_testmode_on(st, chan->idx,
> +				if (ret)
> +					return ret;
> +			} else if (mode == AN877_ADC_TESTMODE_PN23_SEQ) {
> +				ret = ad9467_backend_testmode_on(st, chan->idx,
>  							 IIO_BACKEND_ADI_PRBS_23A);
> -			if (ret)
> -				return ret;
> +				if (ret)
> +					return ret;
> +			}
>  		}
>  	}
>  
> @@ -1263,8 +1271,10 @@ static void ad9467_debugfs_init(struct iio_dev *indio_dev)
>  	if (!st->chan_test)
>  		return;
>  
> -	debugfs_create_file("calibration_table_dump", 0400, d, st,
> -			    &ad9467_calib_table_fops);
> +	if (iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION)) {
> +		debugfs_create_file("calibration_table_dump", 0400, d, st,
> +				    &ad9467_calib_table_fops);
> +	}
>  
>  	for (chan = 0; chan < st->info->num_channels; chan++) {
>  		snprintf(attr_name, sizeof(attr_name), "in_voltage%u_test_mode",

Change the permissions for in_voltage%u_test_mode so that is WO in case we can't
IIO_BACKEND_CAP_CALIBRATION. You can even reuse the above check to tweak the permissions
accordingly. Then no need to check for the capability in ad9467_chan_test_mode_read()

- Nuno Sá