Re: [PATCH 1/2] dt-bindings: iommu/rockchip: Make clock properties optional

[Heiko Stuebner <heiko-4mtYJXux2i+zQB+pC5nmwQ@public.gmane.org>]

Am Freitag, 13. April 2018, 23:02:26 CEST schrieb Rob Herring:
> On Tue, Apr 10, 2018 at 01:26:41PM +0200, Heiko Stuebner wrote:
> > Hi Robin,
> > 
> > Am Dienstag, 10. April 2018, 13:18:48 CEST schrieb Robin Murphy:
> > > On 10/04/18 10:26, Heiko Stuebner wrote:
> > > > Rockchip IOMMUs are used without explicit clock handling for 4 years
> > > > now, so we should keep compatibility with old devicetrees if possible.
> > > > Therefore make iommu clocks optional.
> > > 
> > > Do we need to touch the binding itself? Obviously the driver has to 
> > > treat clocks as optional in existing DTs (and I feel a bit dumb now for 
> > > managing to overlook that in review), but the binding effectively only 
> > > covers future DTs, and I'd assume we want to encourage the clocks to be 
> > > correctly specified there.
> 
> I'd prefer the DT docs reflect what is correct for new/current dts 
> files. That's the only way the docs can validate the dts files.
> 
> > I guess that depends on your definition of the timespan for backwards
> > compatibility. I'm always starting out at indefinite till convinced
> > otherwise ;-). Hence the clocks would need to stay optional for (nearly)
> > forever.
> > 
> > Also, having the binding claim them as required but the code handling
> > them as optional just calls for someone to remove the optional handling :-D
> 
> A comment in the code saying why missing clocks are allowed should 
> suffice.
> 
> > Not sure if there is a established way of saying
> > "we want this for all future devices, but allow it to be missing for old dts".
> 
> We don't really...

Ok, I'll drop the binding change and add a code comment then.


Heiko