[PATCH v2 07/10] dts/ls2085a: Update DTSI to add support of various peripherals

[Scott Wood]

On Thu, 2015-10-01 at 17:41 -0500, Li Yang wrote:
> On Thu, Oct 1, 2015 at 4:58 PM, Scott Wood <scottwood at freescale.com> wrote:
> > On Thu, 2015-10-01 at 16:42 -0500, Li Yang wrote:
> > > On Thu, Oct 1, 2015 at 3:05 PM, Stuart Yoder <stuart.yoder at freescale.com>
> > > 
> > > wrote:
> > > > Hi Rob,
> > > > 
> > > > Had a question about your comments on the patch below.
> > > > 
> > > > You singled out 3 nodes (gic,uart,clockgen) and said "This should be
> > > > under a bus node."
> > > > 
> > > > What is special about those 3 nodes types?  There are a bunch of other
> > > > memory
> > > > mapped SoC devices as well in the DTS.
> > > > 
> > > > I skimmed the dts files under arch/arm64 and it looks like most have a
> > > > simple-bus
> > > > SoC node like this where SoC devices are under:
> > > > 
> > > >         soc {
> > > >                 #address-cells = <2>;
> > > >                 #size-cells = <2>;
> > > >                 compatible = "simple-bus";
> > > >                 ranges;
> > > > 
> > > > Is that what you are looking for-- for all SoC devices?
> > > 
> > > I think the key is to have the soc node and have all the on-chip
> > > devices defined underneath it.
> > > 
> > > I read the following from the booting-without-of.txt document:
> > > 
> > >   f) the /soc<SOCname> node
> > > 
> > >   This node is used to represent a system-on-a-chip (SoC) and must be
> > >   present if the processor is a SoC. The top-level soc node contains
> > >   information that is global to all devices on the SoC. The node name
> > >   should contain a unit address for the SoC, which is the base address
> > >   of the memory-mapped register set for the SoC. The name of an SoC
> > >   node should start with "soc", and the remainder of the name should
> > >   represent the part number for the soc.  For example, the MPC8540's
> > >   soc node would be called "soc8540".
> > > 
> > > A lot of device trees didn't follow the soc<SOCname> naming scheme and
> > > just used "soc" as the node name.  I am not sure if we want to enforce
> > > the naming in the future or update the document to make it more relax.
> > 
> > Update the document.  Having the SoC name in the node name was a pain, 
> > which
> > is why we don't do it anymore.  Ideally, this text should be moved into a
> > binding for Freescale PPC/LS SoCs.  It really doesn't have the broad
> > applicability that this historical document suggests, and even on our 
> > SoCs it
> > doesn't represent the entire SoC.  It represents CCSR/IMMR.
> 
> Having the soc node to represent the CCSR space is a Freescale
> specific thing.  But using the soc node to be the parent for all the
> on-chip devices seems to be a good practice for all device trees.  I
> do think we should maintain a standard for the top level nodes of a
> device tree.

But it doesn't represent all on-chip devices.  E.g. DPAA portals don't go 
under it, because they're not part of CCSR.  DCSR doesn't go under it, etc.  
If the definition doesn't even work for our own SoCs, how are we going to 
force it on everyone else's?

-Scott