Re: [PATCH 7/7] ARM: dts: sun7i: Add dts file for the A20-linova1-7 HMI

[Maxime Ripard]

On Fri, May 04, 2018 at 11:52:59PM +0200, Giulio Benetti wrote:
> Hi Maxime!
> 
> Il 04/05/2018 10:06, Maxime Ripard ha scritto:
> > Hi,
> > 
> > On Wed, May 02, 2018 at 06:41:34PM +0200, Giulio Benetti wrote:
> > > > > You don't have to handcode the fragments anymore with the new syntax,
> > > > > and U-Boot makes it really trivial to use if you use the FIT image
> > > > > format to have multiple overlays bundled in the same image. You can
> > > > > choose to apply them dynamically, for example based on an EEPROM or
> > > > > some other metric to see which combination you have.
> > > > 
> > > > Ah, this is interesting. I'm going to experiment with that.
> > > > 
> > > 
> > > I'm struggling against this, I don't really know how to proceed,
> > > except keeping monolithic dts files including other dtsi files.
> > > 
> > > About dt-overlays I've tried to look around lot of time,
> > > but the only thing I've found is this:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/tree/arch/arm/boot/dts?h=topic/renesas-overlays
> > > 
> > > where they use .dtso tagging them as "/plugin/;"
> > > and compile all .dtso found in dts folder.
> > > Then they obtain .dtbo files that should be the dt-overlays we have spoken
> > > about right?
> > 
> > Yes. You don't have to do that though, you can just rely on dtc to
> > compile them, outside of the linux build system.
> > 
> > > What I can't understand is if there's a real standard at this time to
> > > follow, because on renesas-driver they use their way to handle all .dtso
> > > files, but on mainline there seems to be nothing about that.
> > 
> > I'm not sure what you mean here. It's just fragments of device tree,
> > that have to be compiled using dtc, that's it. You can use the Linux
> > build system infrastructure to do that, or you can build your own
> > simpler one. That's really up to you. See for example
> > https://github.com/NextThingCo/CHIP-dt-overlays/blob/master/Makefile
> > 
> > (even though the overlays themselves use the legacy syntax and
> > shouldn't really be used an examples)
> 
> Everything works now!
> Thank you very much!
> I've setted up a Repo on Github to give an example on how make it work with
> no pain:
> https://github.com/micronovasrl/linova-dtoverlays
> 
> At the moment it's a mess all around, but it's working and give an idea on
> how to make it work. Though I'm going to clean it up well as a base for
> linova dtoverlays.
> 
> Ah, btw, can you confirm me that base dts file must be compiled outside
> kernel with:
> dtc -@ ....
> Otherwise as in-tree dts with make dtbs "-@" argument is not passed.
> Right?

You should use DTC_FLAGS='-@'

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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