Re: [PATCH 00/12] sunxi: Devicetree sync from Linux v5.18-rc1

Andre Przywara
2022-04-29T15:26:04Z

On Fri, 29 Apr 2022 10:57:10 -0400
Tom Rini <trini@konsulko.com> wrote:

Hi,

> On Fri, Apr 29, 2022 at 03:51:59PM +0100, Andre Przywara wrote:
> > On Wed, 27 Apr 2022 15:31:19 -0500
> > Samuel Holland <samuel@sholland.org> wrote:
> >
> > Hi Samuel, Tom,
> >
> > > This series brings all of our devicetrees up to date with Linux.
> > >
> > > Older SoCs (before A83T) have not been synchronized in over 3 years.
> > > And I don't have any of this hardware to test. But there are not major
> > > changes to those devicetrees either.
> > >
> > > The big motivation for including older SoCs in this update is converting
> > > the USB PHY driver to get its VBUS detection GPIO/regulator from the
> > > devicetree instead of from a pin name in Kconfig. Many older boards had
> > > those properties added or fixed since the last devicetree sync. This PHY
> > > driver change is necessary to complete the DM_GPIO migration.
> > >
> > > A couple of breaking changes were made to several SoCs' devicetrees in
> > > Linux relating to the "r_intc" interrupt controller. New kernels support
> > > old devicetrees, but not the other way around. So to be most compatible
> > > and avoid regressions, those changes are skipped here.
> >
> > Many thanks for considering this! I just skimmed over the A64 and H6
> > patches, and this is indeed the only difference.
> >
> > But while I love this pragmatic approach, and would be happy to take this,
> > this goes against our own rules, and more importantly against Tom's one's:
> > to take only direct DT file copies from the kernel tree.
> >
> > Tom, can you give your opinion here? As Samuel mentioned above, the
> > current mainline DTs wouldn't boot on older kernels (the changes affect
> > critical devices), so this spoils stable distro and installer kernels,
> > when using $fdtcontroladdr, for instance when booting via UEFI.
> >
> > As a side effect of always defining SYS_SOC to "sunxi", we cannot easily
> > use per-SoC DT overrides using sun50i-a64-u-boot.dtsi, for instance.
> >
> > For context, those changed properties were in the mainline kernel tree at
> > some point, but have been amended since. So it's not some random change.
>
> So, this is I guess a bit annoying. But, we aren't at the point where
> the common use case is the downstream OS using the DTB we've loaded and
> are using, are we? I mean, we can't be, as ours are so far out of date,
> so this will only be an option when we use a recent DT ourself. So we
> should be able to sync in the changes and update our code, as they can't
> be using $fdtcontroladdr in this case, right? Or am I missing the use
> case that's in the wild atm? Thanks!

While it sounds like the DTs are wildly out of date, this mostly affects
secondary functionality. The mainline updates for the 64-bit SoCs are:
- H6: adding the VP9 video h/w codec and an additional wakeup timer
- A64: adding GPU DVFS, adding DRAM DVFS, add support for secondary
digital audio interfaces, plus the wakeup timer
Also there are cosmetic changes, like changing node names to make them
binding compliant.
So those DT updates are really only important for mobile devices like the
Pinephone, which probably don't use UEFI booting.

At the moment I boot distro grubs and installers just fine, and without
losing any real functionality (minus suspend/resume, maybe). The
out-of-the-box default boot works now, and would break when pulling in the
pure mainline DTs. Plus FreeBSD (which relies more heavily on UEFI, IIUC),
can only deal with the older DTs (#interrupt-cells for r_intc must be 2).

Cheers,
Andre