Re: [PATCH v3 1/2] dt-bindings: iio: dac: Add AD5529R

[Conor Dooley <conor@kernel.org>]

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On Mon, Jun 22, 2026 at 05:29:11PM +0100, Jonathan Cameron wrote:
> > > > Yeah. It's not clear to me how that works for the microchip devices
> > > > (I suspect it doesn't!)
> > > > 
> > > > Just thinking as I type, but could we do something a bit nasty with
> > > > a gpio mux that doesn't actually switch but represents the GPIO being
> > > > shared?  Given this is all tied to the spi bus that should all happen
> > > > under serializing locks. 
> > > > 
> > > > Agreed though that this would be nicer as an SPI thing that let
> > > > us specify that a single CS is share by multiple devices and their
> > > > is some other signal acting to select which one we are talking to.
> > > >   
> > > 
> > > If the device-addressing on the same chip-select is to be handled
> > > by the spi framework, wouldn't we lose device-specific features?
> > > 
> > > I understand that this multi-device feature is there mostly to extend the
> > > channel count from 16 to 32, 48 or 64. I suppose the command:
> > > 
> > > 	"MULTI DEVICE SW LDAC MODE"
> > > 
> > > exists so that software can update channel values accross multiple devices.  
> > 
> > Right! You do have a point! I agree the main driver for a feature like
> > this is likely to extend the channel count and effectively "aggregate"
> > devices.
> > 
> > But I would say that even with the spi solution the MULTI DEVICE stuff
> > should be doable (as we still need a sort of adi,pin-id property). 
> > 
> > But yes, I do feel that the whole feature is for aggregation so seeing
> > one device with 32 channels is the expectation here? Rather than seeing
> > two devices with 16 channels.
> 
> Agreed - if we have messages that address both devices at once that needs
> to be a unified driver and given they are about triggering simultaneous
> update of all channels it needs to look like one big device.
> This ends up similar to how we handle daisy chain devices.
> 
> The question of what to do on devices that don't have this feature
> is rather different. Good thing you read the datasheet :)

I'm not sure it really is, the intent for the microchip devices I think
is pretty similar. The mcp3911 datasheet cites three-phase power
metering using three devices as a typical use-case, for example.
Probably creating an amalgamated device is a good fit there too?

I assume an amalgamated device for this ADI product means per-channel ID
properties? If so, I think they should be made generic and the Microchip
products retrofitted to use them, with a fallback to the proprietary
property. Not going to ask for the support for multiple devices in those
drivers, since the current way doesn't work and there'd be no loss of
support. Someone from Microchip can do that. The proprietary property
to generic conversion should be straightforward and provides weight to
an argument for this being generic, since that'd be three devices that
can all share?

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