[Letux-kernel] Raspi3B+ support in Letux Kernel

H. Nikolaus Schaller hns at goldelico.com
Tue Jan 8 21:59:22 CET 2019

Hi all,

> Am 07.01.2019 um 18:11 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> Hi Levi,
>> Am 07.01.2019 um 17:49 schrieb levi <levi2015 at cobaltlake.co.uk>:
>> On Mon, 7 Jan 2019 17:02:27 +0100
>> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>>> Nevertheless the description of -@ "Enable generation of symbols" is
>>> not very helpful. Why would one enable that? What happens if not?
>>> What are "symbols" etc. Questions over questions...
>> I think it's referring the symbols as in debug symbols, the kind of
>> thing you need to build in in order to get anything sensible out of
>> gdb, assuming it's even possible to debug this.
>> But a bit of internet searching got me to this commit:
>> https://github.com/RobertCNelson/dtc/commit/dd6a0533e846e8d5e690a618fa35cc15a6103efb
>> That says:
>> "This is sufficient to implement a dynamic DT object loader."
>> Whether you actually want that I don't know, and I couldn't tell you
>> how to pass the right option to dtc within the wrapped up tools.
>> But you did ask the question...
> Ok, this description in the commit gives another hint to my current
> theory that the Raspi boot loader needs this information to load the
> DT and modify it before starting the kernel...
> To answer the real question if compiling with -@ makes the DTB bootable
> on RasPI can only be found by trying :)

> With that I can easily compile the bcm2837.dts with -@ option. But only
> after finishing the current work which is rebasing letux to v5.0-rc1
> and debugging my wrongly resolved merge conflicts.

Well, my dtc wrapper did not find all required #includes, but I found
out that I can simply do "DTC_FLAGS=-@ make-linux" which is passed
down to the kernel Makefile and DTC.

With that I now get a __symbols__ section in the DTB. But there
is no __overrides__. Strange, how that is generated from the github
tree. Maybe it is explicitly in some .dtsi there?

Anyways, the 5.0-rc1 kernel still only boots with the .dtb built from
the github tree... (without explict -@ option!).

I have also checked for the uart aliases and now with 5.0-rc1 they are there
for the serial0/1 - but they appear to be swapped. I have tried to swap
them in arch/arm/boot/dts/bcm283x.dtsi, but this makes also no change
in boot log or boot success.

So it is stilly a mystery what makes the device trees so different.

I have attached both versions (reverse compiled from .dtb), if someone
wants to look into them. Sometimes 10 eyes see more than two...


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