[U-Boot] [PATCH v2 3/5] sunxi: DT: A64: update device tree file for Allwinner A64 SoC

[Andre Przywara]

On Wed, 17 Oct 2018 17:29:58 +0200
Maxime Ripard <maxime.ripard at bootlin.com> wrote:

Hi,

> On Wed, Oct 17, 2018 at 04:18:41PM +0100, Andre Przywara wrote:
> > On Tue, 16 Oct 2018 22:09:30 -0700
> > Vasily Khoruzhick <anarsoul at gmail.com> wrote:
> > 
> > Hi,
> >   
> > > Updates the device tree file from the the Linux tree as of
> > > v4.19-rc4, exactly Linux commit:  
> > 
> > Does this work easily without syncing the .dts files as well?
> >   
> > > commit 7876320f8880 (tag: v4.19-rc4)
> > > Author: Linus Torvalds <torvalds at linux-foundation.org>
> > > Date:   Sun Sep 16 11:52:37 2018 -0700
> > > 
> > >     Linux 4.19-rc4  
> > 
> > So this sounds like the right thing to do, but in this particular
> > case breaks Ethernet with UEFI booting in all distribution
> > installers or kernels out there (except >= Linux 4.19-rc1).
> > I consider this a major use case of U-Boot's DTB, so what do we do
> > about this?
> > The reason is that we dropped the "syscon" compatible string at the
> > end of the system-controller node, which older kernels rely on to
> > find the syscon node.
> > I suggested to re-add this[1], but didn't have much success,
> > unfortunately.
> > The easiest would be to re-add (or not remove) "syscon" for U-Boot's
> > copy, but this would mean a deviation from the Linux DT's. I am fine
> > with this, but would like to hear more opinions.  
> 
> tl; dr: You want to build something robust on top of assumptions that
> have never been guaranteed.

I just find it sad that "we do not guarantee" translates into "we
actually don't even try". My understanding of your concern is that you
can't rule this breakage out forever, which I can understand.
But if it is possible to avoid breaking compatibility, I believe we
should try this, on a case-by-case base. 
We have been pretty good so far (leaving alone the MMC regulator
breakage in v4.15, but A64 support was quite basic before that anyway).

> I'm fine with having it as a U-Boot
> addition, if it's what it takes.

Sounds good to me! Thanks!

I will check what's the easiest path to get the 4.20 DTs into U-Boot,
considering a stopover at the Pinebook DTs, and send patches ASAP.

Cheers,
Andre.