[U-Boot] [PATCH 1/2] fdt: Allow indicating a node is for U-Boot proper only

[Patrick DELAUNAY]

Hi Marek,

> From: Marek Vasut <marex at denx.de>
> Sent: mardi 5 février 2019 09:55
> 
> On 2/4/19 3:40 PM, Simon Glass wrote:
> > On Mon, 4 Feb 2019 at 03:15, Patrick Delaunay <patrick.delaunay at st.com>
> wrote:
> >>
> >> This add missing parts for previous commit 06f94461a9f4
> >> ("fdt: Allow indicating a node is for U-Boot proper only")
> >>
> >> At present it is not possible to specify that a node should be used
> >> before relocation (in U-Boot proper) without it also ending up in SPL
> >> and TPL device trees. Add a new "u-boot,dm-pre-proper" boolean property
> for this.
> >>
> >>
> >> Signed-off-by: Patrick Delaunay <patrick.delaunay at st.com>
> >
> > Reviewed-by: Simon Glass <sjg at chromium.org>
> >
> > There was discussion some time ago about using a property instead:
> >
> > chosen {
> >    u-boot,dm-spl = <&node1 &node2>;
> >     u-boot,dm-tpl = <&node1>;
> > };
> >
> > At the time I decided that this was more painful since it separates
> > out the tag from its node.
> >
> > I wonder if that is still true? We do now in fact generally use a
> > u-boot.dtsi file to hold these tags.
> >
> > I'm not suggesting a change, just raising the question.
> 
> It's a good suggestion. In fact, you can then use some tool to walk back up the
> tree and only retain the branches which are referenced by phandle from u-
> boot,dm-spl/tpl node for U-Boot SPL/TPL DTs. I think that could save a bit of
> space too. I wonder if we can even use /omit-if-no-ref/ DTC syntax somehow.

If I correctly understood the new feature of dtc "/omit-if-no-ref/",  in kernel dtc since 4.18,
dtc remove node when nobody use reference on this node, so it is useful for U-Boot
nodes when they are used as reference : for example pincontrol nodes.
cf: https://elinux.org/Device_Tree_Source_Undocumented

U-Boot dtb use dtc to compile dts files , so it can be used here.

But for SPL / TPL the parsing in done in fdtgrep, on dtb
And the tags  "/omit-if-no-ref/" are already removed in dtb.

NB: we could also remove the tags u-boot,dm-pre-reloc/u-boot,dm-spl  : we can gain place in spl dtb
       These tags are not needed as binding is mandatory in SPL build for ALL node  present in SPL device tree 
      others node are cleaned by fdtgrep (but impact in SPL code) 

PS: a other boring point: if we need to tag all the tree to have one sub-node in SPL
      For me spl tag on the children should be enough ...
      But is perhaps difficult in ftdgrep (need to parse all the fathers node)

      For example to have pins1 and pins2,
      we have to also tag qspi-bk2-0 and pin-controller
 
        pin-controller at 50002000 {
            u-boot,dm-pre-reloc;
            qspi-bk2-0 {
                u-boot,dm-spl;
                pins1 {
                    u-boot,dm-spl;
                };
                pins2 {
                    u-boot,dm-spl;
                };
            };
         };

> --
> Best regards,
> Marek Vasut