Re: [PATCH v2 11/11] iio: dac: support the ad9739a RF DAC

["Nuno Sá" <noname.nuno@gmail.com>]

On Sat, 2024-04-06 at 17:41 +0100, Jonathan Cameron wrote:
> On Fri, 5 Apr 2024 17:00:09 +0200
> Nuno Sa <nuno.sa@analog.com> wrote:
> 
> > The AD9739A is a 14-bit, 2.5 GSPS high performance RF DACs that are capable
> > of synthesizing wideband signals from DC up to 3 GHz.
> > 
> > A dual-port, source synchronous, LVDS interface simplifies the digital
> > interface with existing FGPA/ASIC technology. On-chip controllers are used
> > to manage external and internal clock domain variations over temperature to
> > ensure reliable data transfer from the host to the DAC core.
> > 
> > Co-developed-by: Dragos Bogdan <dragos.bogdan@analog.com>
> > Signed-off-by: Dragos Bogdan <dragos.bogdan@analog.com>
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
> The only thing I really have remaining questions on is the choice
> of chan_spec with altvoltage and voltage channels.  Why does that
> split make sense?  It's odd enough that some comments in the code would
> be a good thing to add.
> 
> Jonathan
> 
> > new file mode 100644
> > index 000000000000..9b91d66f826c
> > --- /dev/null
> > +++ b/drivers/iio/dac/ad9739a.c
> > @@ -0,0 +1,454 @@
> 
> > +
> > +static struct iio_chan_spec ad9739a_channels[] = {
> > +	{
> > +		.type = IIO_ALTVOLTAGE,
> 
> So this looks a little unusual. Perhaps some comments on why it
> is appropriate to have this channel.
> 
> In reality there is only one channel I think?

Yeah, I had this same discussion internally and was also thinking in having one
channel (just ALTVOLTAGE). I ended up doing it as we have done it internally so
far. The reasoning is that we have two sources of data:

ALTVOLTAGE: It's the internally continuous wave the backend can generate. That
is in fact alternate voltage.

VOLTAGE: Is kind of what I call external source where we assume is just typical
DAC data and that typically is VOLTAGE (but for a dac like this, I think it may
very well be, if not most of the time, also alternate - the thing is, we can't
know for sure as we should be able to have both)

- Nuno Sá