[Ksummit-discuss] Devicetree Workshop at Kernel Summit Prague (26 Oct 2017)

[David Gibson]

On Fri, Oct 20, 2017 at 08:37:26AM -0500, Rob Herring wrote:
> On Fri, Oct 20, 2017 at 4:55 AM, Alexandre Torgue
> <alexandre.torgue at st.com> wrote:
> > Hi Frank,
> >
> >
> > On 10/19/2017 08:46 PM, Frank Rowand wrote:
> >> On 10/19/17 07:59, Rob Herring wrote:
> >>> On Thu, Oct 19, 2017 at 9:00 AM, Alexandre Torgue
> >>> <alexandre.torgue at st.com> wrote:
> >>>>
> >>>> Hi Rob,
> >>>>
> >>>>
> >>>> On 10/19/2017 01:53 AM, Rob Herring wrote:
> >>>>> On Wed, Oct 18, 2017 at 6:28 PM, Andrew Turner <andrew at fubar.geek.nz>
> >>>>> wrote:
> >>>
> >>>
> >>> [...]
> 
> >>>>          -->For example, I want to use the same dtsi files between Linux
> >>>> and
> >>>> U-boot. If in u-boot dts file I overload several "status" entry by
> >>>> "disabled", is it possible that compiler doesn't build it ? And what
> >>>> about
> >>>> not used phandle ?
> >>>
> >>>
> >>> You certainly could remove disabled nodes in dtc. I'm not sure how
> >>> hard it would be to plumb into dtc. I think phandle properties are
> >>> already only created if there's a reference to them. If that is
> >>
> >>
> >> Yes, phandles are only created if referenced, unless compiled
> >> for loading overlays into:
> >>
> >
> > Are there DTC "extra" options to use to not build those useless phandles ? I
> > just tried to revert the dtb to dts (using following command:
> >  ./scripts/dtc/dtc -I dtb -O dts -o stm32f469-disco-flat.dts
> > arch/arm/boot/dts/stm32f469-disco.dtb)
> >
> > I see that phandles not used are in the dts output file. It is especially an
> > issue for pinmux phandles. All pinmux groups possibilities are written
> > inside (in my case) stm32f4-pinctrl.dtsi. This file is included in each
> > stm32 board dts files, and in those stm32 board dts files only required node
> > are enabled. But I see that all pinmux definitions are embedded inside dtb
> > binary (even ones not used in board dts file).
> 
> Ah, you mean removing nodes without a phandle reference, not phandles
> themselves.
> 
> There's no way dtc could do that because no reference doesn't equate
> to unused. For example, there's no phandle reference to the /memory
> node, but that is for sure needed. We would have to add some
> annotation to nodes that could be removed if unused. This could be
> some source annotation (/delete-if-unused/), some extension to status
> property, or some new property.
> 
> Another option would be just mark all those nodes disabled and then
> postprocess the dtb to mark them okay if they have a phandle property
> and delete the node if not.

I'd be happy enough to merge a patch to dtc which added an option to
strip disabled nodes.  It's also pretty easy to do using libfdt (see
fdt_next_node() and fdt_del_node()).

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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