Re: [RFC PATCH 0/3] Add converter framework

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 30 Aug 2023 17:29:03 +0100
Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:

> On Fri, 4 Aug 2023 16:53:38 +0200
> Nuno Sa <nuno.sa@analog.com> wrote:
> 
> > This is the initial RFC following the discussion in [1]. I'm aware this is
> > by no means ready for inclusion and it's not even compilable since in
> > the RFC I did not included the patch to add component_compare_fwnode()
> > and component_release_fwnode().   
> 
> Whilst I haven't read this through yet, I suspect Olivier will be able to
> offer some insight on some of this and likewise you may be able to
> point out pitfalls etc in his series (I see you did some review already :)
> 
> https://lore.kernel.org/linux-iio/20230727150324.1157933-1-olivier.moysan@foss.st.com/
> 
> Both are about multiple interacting components of an overall datapath.
> Whether there is commonality isn't yet clear to me.
Works better if I actually remember to CC Olivier.

+CC Olivier!
> 
> > 
> > The goal is to have a first feel on the
> > direction of the framework so that if I  need to drastically change it,
> > better do it now. The RFC also brings the ad9647 and the axi_adc core to
> > the same functionality we have now upstream with one extra fundamental
> > feature that is calibrating the digital interface. This would be very
> > difficult to do with the current design. Note that I don't expect any
> > review on those drivers (rather than things related to the framework). 
> > 
> > I also want to bring up a couple of things that I've
> > been thinking that I'm yet not sure about (so some feedback might make
> > mind in one direction or another).
> > 
> > 1) Im yet not sure if I should have different compatibles in the
> > axi-adc-core driver. Note this soft core is a generic core and for every
> > design (where the frontend device changes or has subtle changes like
> > different number of data paths) there are subtle changes. So, the number
> > of channels might be different, the available test patterns might be
> > different, some ops might be available for some designs but not for
> > others, etc...   
> 
> I don't suppose there is any chance Analog can make at least some of this
> discoverable from the hardware?  Capability registers etc in the long
> run. Can't fix what is already out there.
> 
> > With a different compatible we could fine tune
> > those differences (with a chip_info like structure) and pass some const
> > converter_config to the framework that would allow it to do more safety
> > checks and potentially reduce the number of converter_ops.
> > OTOH, starting to add all of these compatibles might become messy in the
> > long run and will likely mean that we'll always have to change both
> > drivers in order to support a new frontend. And the frontend devices
> > should really be the ones having all the "knowledge" to configure the
> > soft core even if it means more converter_ops (though devicetree might
> > help as some features are really HW dependent). I more inclined to just
> > leave things as-is in the RFC.  
> 
> I'm fine with putting this stuff in DT where possible.
> 
> > 
> > 2) There are some IIO attributes (like scale, frequency, etc) that might
> > be implemented in the soft cores. I still didn't made my mind if I should just
> > have a catch all read_raw() and write_raw() converter_ops or more fine
> > tuned ops. Having the catch all reduces the number of ops but also makes
> > it more easier to add stuff that ends up being not used anymore and then
> > forgotten. There are also cases (eg: setting sampling frequency) where
> > we might need to apply settings in both the frontend and the backend
> > devices which means having the catch all write_raw() would be more
> > awkward in these case. I'm a bit more inclined to the more specific ops.   
> 
> It's the kernel - we can always change the internal API later as long as we
> don't touch the user space part.  Go with your gut feeling today and
> if it changes this sort of refactor usually isn't that bad.
> 
> > 
> > 3) I also placed this in addac as this is mostly used in high speed DACs
> > and ADCs but maybe we should just have it in the top level directory
> > just in case this is started to be used in different type of devices?  
> 
> Easy to change later so right now I don't care where it is.
> 
> > 
> > 4) Some function and data names are also starting to become very big so
> > if there are no objections I will move all to use conv instead of full
> > converter. Or maybe something a bit more generic (converter is a bit specific
> > I know)?  
> 
> Abrv. fine as long as consistenty used.
> 
> > 
> > I would love to hear some ideas about the above...
> > 
> > Anyways, I should also mention that the only visible ABI breakage is in
> > the IIO device name. Before it was named "adi-axi-adc" and now it's
> > "ad9647" which is what makes sense actually. With the current approach
> > we would not be able to actually distinguish between designs.   
> 
> Given that will probably only result in support calls to ADI I'm fine with
> that breakage. :)
> 
> > 
> > So my plan for the actual series will be to just add the framework and migrate
> > the current drivers to it with the same functionality as they have now (not
> > sure if it will be viable to migrate the drivers in a way each commit is
> > functional - unless we convert both drivers in one commit).  
> Make sure they build. It's fine to end up with some non functional stubs
> during such a migration.
> 
> > After that
> > point, I will start adding all the missing features (and devices) to the
> > ad9467 driver. To note that I also plan to include the axi-dac driver in
> > the first series and that will require IIO DMA output buffer support
> > so we might need to cherry-pick those patches from Paul's DMABUF series.  
> As mentioned in reply to that, I'm fine with you carrying Paul's miniseries
> in your patch set to make this all easy to manage.
> 
> Jonathan
> 
> > 
> > Thanks!
> > - Nuno Sá
> > 
> > [1]: https://lore.kernel.org/linux-iio/dac3967805d7ddbd4653ead6d50e614844e0b70b.camel@gmail.com/
> > 
> > Nuno Sa (3):
> >   iio: addac: add new converter framework
> >   iio: adc: ad9647: add based on converter framework
> >   iio: adc: adi-axi-adc: add based on new converter framework
> > 
> >  drivers/iio/adc/ad9467_new.c        | 830 ++++++++++++++++++++++++++++
> >  drivers/iio/adc/adi-axi-adc-new.c   | 405 ++++++++++++++
> >  drivers/iio/addac/converter.c       | 547 ++++++++++++++++++
> >  include/linux/iio/addac/converter.h | 485 ++++++++++++++++
> >  4 files changed, 2267 insertions(+)
> >  create mode 100644 drivers/iio/adc/ad9467_new.c
> >  create mode 100644 drivers/iio/adc/adi-axi-adc-new.c
> >  create mode 100644 drivers/iio/addac/converter.c
> >  create mode 100644 include/linux/iio/addac/converter.h
> >   
>