[Letux-kernel] Raspi3B+ support

[H. Nikolaus Schaller]

Hi,

> Am 05.01.2019 um 08:21 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> Hi Andreas,
> 
>> Am 04.01.2019 um 20:27 schrieb Andreas Kemnade <andreas at kemnade.info>:
>> 
>> Hi,
>> 
>> On Fri, 4 Jan 2019 14:45:47 +0100
>> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>> 
>>> Hi,
>>> with help and suggestions from Mark, I finally managed
>>> to get our Letux kernel compile and boot on the Raspi3B+.
>>> 
>> Do you add -@ to DTC_FLAGS to make handling dtb overlays easier?
> 
> You mean something like:
> 
> https://github.com/beagleboard/meta-beagleboard/blob/master/common-bsp/recipes-kernel/linux/linux-mainline-3.8/not-capebus/0021-OF-Compile-Device-Tree-sources-with-resolve-option.patch
> 
> No, since mainline kernel seems not to build or need any overlays
> for RasPi and I am not (yet) aiming at shield/hat/capes. Just a "PC"
> like setup (monitor, keyboard, LAN).
> 
> But according to DT contents, Ethernet and USB and maybe WLAN should
> be supported by v4.20. Maybe I am still missing some CONFIGs.
> 
> Most people are building the github raspi kernel trees or the
> debian buster kernel and therefore describe only that in their
> how-tos. But it doesn't directly help us to integrate RasPi
> support into the Letux Kernel.
> 
> What I have not yet verified is if we load the correct DTB
> (there is no log entry telling a file name).

Well, I have tried to find out and there are two .dtb for the
Raspi B3+ built by my setup:

root at letux:~# ls -l /boot/bcm2*rpi-3-b-plus*
-rwxr-xr-x 1 root root 25399 Jan  5  2019 /boot/bcm2710-rpi-3-b-plus.dtb
-rwxr-xr-x 1 root root 19655 Jan  5  2019 /boot/bcm2837-rpi-3-b-plus.dtb
root at letux:~# 

After adding a tag string to the DTS I can check which one is loaded by
default (i.e. some rule built into the bootloader):

root at letux:~# echo $(cat /proc/device-tree/dts)
bcm2710-rpi-3-b-plus.dts
root at letux:~# 

So although bcm2837 is printed on the CPU chip it loads the bcm2710.dtb
What I do not yet understand is why they are different... And why choosing
bcm2837-rpi-3-b-plus.dtb by config.txt does not even boot.

BTW: neither USB, Ethernet and WLAN are working on the github raspi
tree. Maybe it is because the bcm2837-rpi-3-b-plus.dtb is not loaded...

BR,
Nikolaus