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Bug#910727: Overlays cannot be applied to dtbs - missing DTC_FLAGS='-@'

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  Bug#910727: Overlays cannot be applied to dtbs - missing DTC_FLAGS='-@' Nicolas Frattaroli <frattaroli.nicolas@gmail.com> - 2023-02-12 19:00 +0100
    Bug#910727: Overlays cannot be applied to dtbs - missing DTC_FLAGS='-@' Diederik de Haas <didi.debian@cknow.org> - 2023-07-31 10:10 +0200

#78251 — Bug#910727: Overlays cannot be applied to dtbs - missing DTC_FLAGS='-@'

Hello,

I realise this is quite an old bug, but it would still be of interest
to me to get this enabled. The -@ option will increase the size of the
compiled device tree blobs somewhat, but on the flipside, u-boot-menu's
device tree overlay functionality will actually be useful.

In my case, I'm interested in this for PINE64's Quartz64 lineup of ARM
devices. Since these are development boards that expose non-enumerating
protocols like I2C and SPI, the use of device tree overlays is pretty
much required to add additional modules to the board.

Kind regards,
Nicolas Frattaroli

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#79824

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On Monday, 31 July 2023 04:28:31 CEST MOESSBAUER, Felix wrote:
> On Sun, 12 Feb 2023 18:52:07 +0100 Nicolas Frattaroli
> <frattaroli.nicolas@gmail.com> wrote:
> > I realise this is quite an old bug, but it would still be of interest
> > to me to get this enabled. The -@ option will increase the size of
> > the compiled device tree blobs somewhat, but on the flipside, 
> > u-boot-menu's device tree overlay functionality will actually be useful.
> 
> The increase is around 30% in average. For the linux-image-6.1.0-10-
> arm64, we have around 30MB of dtb files (uncompressed). By that, the
> package would grow by 10MB (uncompressed) or even less when compressed.

I'm not a kernel maintainer, but I wouldn't expect it to be applied to 
Debian's Stable kernel, ie the 6.1 series.

> On many (if not most) arm based boards, these device tree overlays are
> very useful. There are also many kernel patches about enabling the
> symbol support on a per-device basis. However, kernel devs seem to have
> some mixed feelings about that. A proposed solution is to enable this
> at distro level [1].
> @Ben: Would it be an accepted solution to enable the DTC_FLAGS += -@
> for all armhf, armmp, arm64 and riscv devices?

AFAIUI, the upstream kernel devs were against such a blanket enablement.
(Consequently it sounds like a bad idea if Debian would do it)

https://lore.kernel.org/all/20220328000915.15041-1-ansuelsmth@gmail.com/ was a 
renewed attempt at restructuring the various .dts* into vendor directories and 
with 6.5 that got merged into the upstream kernel.
And (AFAIUI) that was seen as a prerequisite to start enabling the "-@" flag on 
a vendor/directory level, with optionally a subselection if it didn't make 
sense to enable it for all boards ... pretty much (exactly) as you proposed.

Doing it at the distro level was rejected (at least for Debian) with the 
argument that it should be done upstream.
As there is some (?) coordination/synchronization wrt DeviceTrees between the 
upstream kernel and u-boot, that also seems required for the functionality 
quoted at the top of this email.

You mentioned you proposed it for RISC-V boards and some DDs proposed it for 
RPi boards and both got accepted. I think/expected that we would see (many?) 
more such patches getting accepted going forward now that the above mentioned 
dts directory restructuring has taken place.

IOW: I agree with the reasoning you brought up in your patch submission thread 
and keep targeting inclusion in the upstream kernel.

Cheers,
  Diederik

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