Re: [PATCH v2 1/9] dt-bindings: iio: dac: ad3552r: add io-backend property

["Nuno Sá" <noname.nuno@gmail.com>]

On Mon, 2024-09-09 at 13:46 +0100, Conor Dooley wrote:
> On Sun, Sep 08, 2024 at 01:29:25PM +0100, Jonathan Cameron wrote:
> > On Thu, 05 Sep 2024 17:17:31 +0200
> > Angelo Dureghello <adureghello@baylibre.com> wrote:
> > 
> > > From: Angelo Dureghello <adureghello@baylibre.com>
> > > 
> > > There is a version AXI DAC IP block (for FPGAs) that provides
> > > a physical bus for AD3552R and similar chips. This can be used
> > > instead of a typical SPI controller to be able to use the chip
> > > in ways that typical SPI controllers are not capable of.
> > > 
> > > The binding is modified so that either the device is a SPI
> > > peripheral or it uses an io-backend.
> > > 
> > > Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
> > 
> > >  
> > >  required:
> > >    - compatible
> > > -  - reg
> > > -  - spi-max-frequency
> > Sort of feels like both reg and spi-max-frequency
> > are valid things to specify. 
> > 
> > Maybe we have an excellent IP and dodgy wiring so want
> > to clamp the frequency (long term - don't need to support
> > in the driver today).
> > 
> > Maybe we have an axi_dac IP that supports multiple
> > front end devices?  So maybe just keep reg?
> 
> I'd like to be convinced that this incarnation of the AXI DAC IP is not
> a spi controller and that a ref to spi-controller.yaml is not out of
> place here. It may not be something that you'd ever use generally, given
> the "weird" interface to it, but it does seem to be one regardless.
> 

Agreed.. As weird as it get's, it's acting as a spi controller.

> I'd also really like to know how this fits in with spi-offloads. It
> /feels/, and I'd like to reiterate the word feels, like a rather similar
> idea just applied to a DAC instead of an ADC.

The offload main principle is to replay a spi transfer periodically given an
input trigger. I'm not so sure we have that same principle in here. In here I
guess we stream data over the qspi interface based on SCLK which can look
similar. The difference is that this IP does not need any trigger for any spi
transfer replay (I think). 

- Nuno Sá