Re: [PATCH 1/4] dt-bindings: rng: add generic bindings for MediaTek SoCs

[Matthias Brugger]

On 07/06/17 15:20, Sean Wang wrote:
> On Tue, 2017-06-06 at 13:07 +0200, Matthias Brugger wrote:
> > On 31/05/17 20:44, sean.wang@xxxxxxxxxxxx wrote:
> > > From: Sean Wang <sean.wang@xxxxxxxxxxxx>
> > >
> > > Add the generic binding for allowing the support of RNG on MediaTek SoCs
> > > such as MT7622.
> > >
> > > Signed-off-by: Sean Wang <sean.wang@xxxxxxxxxxxx>
> > > ---
> > >    Documentation/devicetree/bindings/rng/mtk-rng.txt | 3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/rng/mtk-rng.txt b/Documentation/devicetree/bindings/rng/mtk-rng.txt
> > > index a6d62a2..0772913 100644
> > > --- a/Documentation/devicetree/bindings/rng/mtk-rng.txt
> > > +++ b/Documentation/devicetree/bindings/rng/mtk-rng.txt
> > > @@ -2,7 +2,8 @@ Device-Tree bindings for Mediatek random number generator
> > >    found in Mediatek SoC family
> > >    
> > >    Required properties:
> > > -- compatible	    : Should be "mediatek,mt7623-rng"
> > > +- compatible	    : Should be "mediatek,generic-rng" or
> > > +				"mediatek,mt7623-rng".
> >
> > What does generic-rng mean. Is it for all mt7xxx, or also for mt6xxx and
> > mt8xxx based SoCs? I think we should stick with SoC specific bindings,
> > as we don't know if Mediatek won't publish a new IP block next year
> > which is differnet.
>
> Yes, what I mean is generic-rng can be applied to all
> platform MediaTek provides.
>
>
> > Just in case we should add a binding for the actual SoC + a fallback.
> > For example.
> > - compatible " Should be
> > 	"mediatek,mt7622-rng", 	"mediatek,mt7623-rng" for SoC mt7622
> > 	"mediatek,mt7623-rng" for SoC mt7623
> >
> > This will also eliminate the need of adding mt6722-rng to the driver, as
> > it will use mt7623-rng as fallback. If in the future we realize that
> > mt7622-rng has a extra feature/bug, we can still work around it, without
> > breaking the bindings.
>
> I knew the fallback rules you said here because I saw them being used in
> many drivers such as sysirq and uart driver, such kind of basic drivers.
>
> These drivers are basic enough, various following chipsets almost fall
> back into the oldest one. So the clues let me think the hardware
> interface shouldn't have too much differences among them.
>
> If there is string used like generic-uart or generic-sysirq, it can
> stop we blindly add new string into the binding document when a new
> platform is introduced.
>
> And they easily allows users unfamiliar MediaTek platform (they didn't
> know what the oldest MediaTek chipset is) pick up the right compatible
> string to start bring up the new platform.
>
> The specific one can be added after new feature required is added or
> critical hardware bug is found. Otherwise the generic one can fit
> all generic needs for those.
>
> Those are only opinions, if you don't like it, I still can accept the
> original way as you suggest :)

I can see your reasoning, but the device tree maintainers prefer to have 
the bindings updated for a new SoC. As I mentioned before, just imagine 
next year Mediatek changes the IP block and from now on, it uses the new 
device in all SoCs. In 5 years we would have a binding which states 
'generic' although it is not compatible with any SoC of the last So

So please keep with the bindings as done up to now.

Best regards,
Matthias

> > Makes sense?
> >
> > Regards,
> > Matthias
> >
> > >    - clocks	    : list of clock specifiers, corresponding to
> > >    		      entries in clock-names property;
> > >    - clock-names	    : Should contain "rng" entries;