Re: [PATCH v5 04/11] dt-bindings: iio: adc: add AXP803 ADC bindings

[Chen-Yu Tsai]

On Mon, Oct 29, 2018 at 9:10 PM Quentin Schulz
<quentin.schulz@xxxxxxxxxxx> wrote:
>
> Hi Jonathan,
>
> On Sun, Oct 28, 2018 at 03:40:11PM +0000, Jonathan Cameron wrote:
> > On Wed, 24 Oct 2018 08:56:33 -0500
> > Rob Herring <robh@xxxxxxxxxx> wrote:
> >
> > > On Tue, 23 Oct 2018 21:53:23 +0300, Oskari Lemmela wrote:
> > > > The AXP803 ADC is compatible with AXP813 ADC, but add
> > > > specific compatible for it.
> > > >
> > > > Signed-off-by: Oskari Lemmela <oskari@xxxxxxxxxxx>
> > > > ---
> > > >  Documentation/devicetree/bindings/iio/adc/axp20x_adc.txt | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > >
> > > Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
> >
> > This doesn't seem to have any dependencies with the other patches
> > so applied to the togreg branch of iio.git and pushed out as testing
> > for the autobuilders to ignore.  However I am a little curious to know
> > why we would add the ID and then not use it (that I can see)?
> >
>
> Sometimes with Allwinner (and X-Powers), two IPs seem identical until we
> discover something that is slightly different. When this happens, we
> have to add a compatible to differentiate both. However, we would also
> need to change the Device Tree to change the compatible. We would need
> to handle the driver behaviour for both Device Trees.
>
> So better anticipate a possible difference so that we don't have to do
> some hacks in the driver to handle the device correctly.
>
> As always, Chen-Yu or Maxime may know better so I'm just stating what I
> seem to recall.

With Allwinner stuff (X-Powers included), sometimes the documents are
incomplete or have errors. We tend to add a model-specific compatible
just in case things turn out not to be so compatible, unless someone
has triple-checked everything, documents and actual hardware included.

However we don't actually document these, so this patch isn't strictly
needed. (I suppose this might annoy the device tree binding maintainers.)

ChenYu