Re: [RFC PATCH] staging: iio: ad9832: modernize ABI and remove dds.h dependency

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

+CC: tomasborquez13@gmail.com
for the opportunity to comment about the proposed updates.

On 03/07, Marcelo Schmitt wrote:
> Hello Bhargav,
> 
> On 03/06, Bhargav Joshi wrote:
> > The AD9832 driver currently relies on legacy custom IIO macros defined
> > in dds.h. This triggers checkpatch.pl warnings (NON_OCTAL_PERMISSIONS)
> > and, more importantly, exposes a non-standard sysfs ABI (e.g.,
> > frequency0, frequency1, phase0-3) directly to user space.
> > 
> > This patch removes the custom macros and migrates the driver to standard
> > IIO API mechanisms:
> > - Standard attributes (frequency, phase) now use info_mask_separate.
> > - Non standard specific toggles (frequencysymbol, phasesymbol,
> >   pincontrol) have been migrated to an ext_info array.
> > - Remove dds.h header dependency.
> > - Pointless frequency_scale and phase_scale attributes are dropped as
> >   suggested by Jonathan in
> >   https://lore.kernel.org/linux-iio/20251231180939.422e9e62@jic23-huawei/
> > 
> > NOTE: This patch introduces an intentional ABI changes. The non-standard
> > attributes (out_altvoltage0_frequency0, etc.) have been removed. They
> > are replaced by standard attributes (out_altvoltage0_frequency and
> > out_altvoltage0_phase). Routing to correct register while writing is
> > handled by checking currently active frequencysymbol or phasesymbol.
> > 
> > Testing: This patch has been strictly compile-tested. I do not have
> > access to physical AD9832 hardware. I am submitting this as an RFC to
> > see if these changes are acceptable, and to ask if someone with physical
> > hardware could test thisg and provide a Tested-by tag.
> > 
> > Signed-off-by: Bhargav Joshi <rougueprince47@gmail.com>
> > ---
> > This patch is heavily inspired from discussions in following
> > thread.
> > https://lore.kernel.org/linux-iio/20251215190806.11003-1-tomasborquez13@gmail.com/
> 
> Thanks for making that clear. Still, a change log highlighting the main
> differences between yours and Tomas' patches would have been appreciated.
> 
> By the way, I'm assuming Tomas is fine with you caring on the driver update?
> 
> More comments inline.
> > 
> > Since this is an RFC please let me know if these changes are acceptable.
> > 
> >  drivers/staging/iio/frequency/ad9832.c | 135 +++++++++++++++----------
> >  1 file changed, 80 insertions(+), 55 deletions(-)
> > 
> > diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
> > index b87ea1781b27..066a1b9ee8d5 100644
> > --- a/drivers/staging/iio/frequency/ad9832.c
> > +++ b/drivers/staging/iio/frequency/ad9832.c
> ...
> > -/*
> > - * see dds.h for further information
> > - */
> > +#define AD9832_EXT_INFO(_name, _ident) { \
> > +	.name = _name, \
> > +	.write = ad9832_write_ext_info, \
> Why no .read procedure? I think at least for the
> out_enable/out_altcurrent0_enable attribute we would want a read function.
> 
> > +	.private = _ident, \
> > +	.shared = IIO_SEPARATE, \
> > +}
> >  
> > -static IIO_DEV_ATTR_FREQ(0, 0, 0200, NULL, ad9832_write, AD9832_FREQ0HM);
> > -static IIO_DEV_ATTR_FREQ(0, 1, 0200, NULL, ad9832_write, AD9832_FREQ1HM);
> > -static IIO_DEV_ATTR_FREQSYMBOL(0, 0200, NULL, ad9832_write, AD9832_FREQ_SYM);
> > -static IIO_CONST_ATTR_FREQ_SCALE(0, "1"); /* 1Hz */
> > -
> > -static IIO_DEV_ATTR_PHASE(0, 0, 0200, NULL, ad9832_write, AD9832_PHASE0H);
> > -static IIO_DEV_ATTR_PHASE(0, 1, 0200, NULL, ad9832_write, AD9832_PHASE1H);
> > -static IIO_DEV_ATTR_PHASE(0, 2, 0200, NULL, ad9832_write, AD9832_PHASE2H);
> > -static IIO_DEV_ATTR_PHASE(0, 3, 0200, NULL, ad9832_write, AD9832_PHASE3H);
> > -static IIO_DEV_ATTR_PHASESYMBOL(0, 0200, NULL,
> > -				ad9832_write, AD9832_PHASE_SYM);
> > -static IIO_CONST_ATTR_PHASE_SCALE(0, "0.0015339808"); /* 2PI/2^12 rad*/
> > -
> > -static IIO_DEV_ATTR_PINCONTROL_EN(0, 0200, NULL,
> > -				ad9832_write, AD9832_PINCTRL_EN);
> > -static IIO_DEV_ATTR_OUT_ENABLE(0, 0200, NULL,
> > -				ad9832_write, AD9832_OUTPUT_EN);
> > -
> > -static struct attribute *ad9832_attributes[] = {
> > -	&iio_dev_attr_out_altvoltage0_frequency0.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_frequency1.dev_attr.attr,
> > -	&iio_const_attr_out_altvoltage0_frequency_scale.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_phase0.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_phase1.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_phase2.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_phase3.dev_attr.attr,
> I'd try to split this patch into smaller ones.
> One for updating the frequency and phase channels.
> 
> > -	&iio_const_attr_out_altvoltage0_phase_scale.dev_attr.attr,
> One patch for dropping the _scale attributes.
> 
> > -	&iio_dev_attr_out_altvoltage0_pincontrol_en.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_frequencysymbol.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_phasesymbol.dev_attr.attr,
> > -	&iio_dev_attr_out_altvoltage0_out_enable.dev_attr.attr,
> > -	NULL,
> > +static const struct iio_chan_spec_ext_info ad9832_ext_info[] = {
> > +	AD9832_EXT_INFO("pincontrol_en", AD9832_PINCTRL_EN),
> Why did you drop the comment about making pincontrol_en a DT property?
> Nevertheless, pincontrol_en is another piece I'd put in a separate patch.
> 
> > +	AD9832_EXT_INFO("frequencysymbol", AD9832_FREQ_SYM),
> > +	AD9832_EXT_INFO("phasesymbol", AD9832_PHASE_SYM),
> Maybe I'm missing something but this doesn't seem to follow the suggested ABI.
> https://lore.kernel.org/linux-iio/20251221194358.3284acb4@jic23-huawei/
> Why did you chose this particular naming for the ABI?
> 
> > +	AD9832_EXT_INFO("out_enable", AD9832_OUTPUT_EN),
> I think it is okay to change the enable from device attribute to channel
> attribute in this case since it's staging and this device has only one channel.
> Though, I believe we should call it out_altcurrent0_enable, as proposed on
> Tomas' set. I'd also set this on a separate patch.
> 
> > +	{ }
> >  };
> >  
> > -static const struct attribute_group ad9832_attribute_group = {
> > -	.attrs = ad9832_attributes,
> > +static const struct iio_chan_spec ad9832_channels[] = {
> > +	{
> > +		.type = IIO_ALTVOLTAGE,
> Maybe I've missed something. Didn't the previous review reached the conclusion
> that the channels should be IIO_ALTCURRENT? The datasheet it documents IOUT as
> current output.
> 
> > +		.indexed = 1,
> > +		.channel = 0,
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_FREQUENCY) |
> > +				      BIT(IIO_CHAN_INFO_PHASE),
> > +		.ext_info = ad9832_ext_info,
> > +	},
> >  };
> >  
> >  static const struct iio_info ad9832_info = {
> > -	.attrs = &ad9832_attribute_group,
> > +	.write_raw = ad9832_write_raw,
> No .read_raw ?
> 
> >  };