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>> int ret; >> >> + if (!iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION)) >> + return 0; > > If it isn't supported then isn't any attempt to turn test_mode on an error? > I would return errors from all these calls and only decide it doesn't > matter right at the top of the call stack. I was considering this option too, I will change accordingly. > > In this particular case that's either calibration mode stuff (covered by check > below) or ad9467_chan_test_mod_write() I'd just add a top level check there > on ability to do calibration. Alternative would be to not register the debugfs > at all. Challenge is that is a small ABI break. Do we care? If we had > been doing this from the start we would have just hidden the pointless > interface. > (Key is we can change userspace interfaces, as long no one notices!) The testmodes from device side should still at least be there, only a few of the modes currently have a backend mode, too. > >> + >> ret = iio_backend_data_format_set(st->back, chan, &data); >> if (ret) >> return ret; >> @@ -665,6 +668,9 @@ static int ad9467_backend_testmode_off(struct ad9467_state *st, > }; >> int ret; >> >> + if (!iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION)) >> + return 0; >> + >> ret = iio_backend_chan_disable(st->back, chan); >> if (ret) >> return ret; >> @@ -807,6 +813,9 @@ static int ad9467_calibrate(struct ad9467_state *st) >> bool invert = false, stat; >> int ret; >> >> + if (!iio_backend_has_caps(st->back, IIO_BACKEND_CAP_CALIBRATION)) >> + return 0; > > So this the idea of a stub calibration bothers me a little, but I think > it's more acceptable to do it for this top level call. So keep this one, but > all the others look to me like they should be returning errors. OK > >> + >> /* all points invalid */ >> bitmap_fill(st->calib_map, st->calib_map_size); >> >> @@ -1357,7 +1366,7 @@ static int ad9467_probe(struct spi_device *spi) >> return ret; >> >> ret = devm_iio_backend_request_buffer(&spi->dev, st->back, indio_dev); >> - if (ret) >> + if (ret && ret != -EOPNOTSUPP) > > I don't see any modification of devm_iio_backend_request_buffer() in this > set so why why is it now acceptable to return not supported? > Given the capabilities stuff added, should this not be another capability > we check before trying to request the buffer? Basically because I reasoned that capabilities are more like features rather than single operation. The single operation tells if the capability is there. I reasoned a bit more about this in a related answer replying to Nuno, hopefully you find time to read that explanation and provide your thoughts. And reason it would now be acceptable is that the original code does not account for any optional features within the backends, but now it does. It knows it can work without the buffering, and the return value can tell if it is supported or not. Thanks, Tomas > >> return ret; >> >> ret = devm_iio_backend_enable(&spi->dev, st->back); >> >