device tree on rpi2 not working

[Eric Anholt]

Tim Sander <tim at krieglstein.org> writes:

> Hi
>
> I have already asked a similar question in the raspberry pi forum without an 
> answer so i figured that my question might be a bit to deeply technical for 
> the forums. Besides i am pretty exited about the work on the free graphics 
> driver and would really like to integrate that as time permits later on.
>
> As a hobby project i have put some effort into putting a ptxdist based linux 
> distro for the rpi2 into shape. It allows developing with qt, opencv, 3d 
> accleration (old style) and camera drivers. The repository is at:
> https://gitlab.com/k6devel/ptxdist-raspberry-pi
>
> But when trying to integrate the pwm drivers i noticed that device tree is 
> somehow not working with my solution. Thats where i am stuck and i have no 
> idea whats wrong? I would be really happy if someone could give me a clue.
>
> Thats what i have been trying out so far:
> I have been using the kernel from 
> https://github.com/raspberrypi/linux.git branch rpi-4.1.y
> 829528571fdcfe078fb165c4acd3b585e8e24a99
>
> I extracted a kernel config from a running raspian and got the /proc/config.gz 
> and used this for building the kernel. It boots and all but there is no 
> /proc/device-tree link as with raspbian and device tree overlays are not 
> working either. I know with high confidence by exchaning my kernel on a 
> raspbian installation that with my kernel the device tree initialization fails 
> even on raspbian. So i figure its most likely a kernel problem. But then the 
> kernel seems to have the device tree patches and my config is pretty close...
>
> I also tried to find the original raspbian kernel but even so its running a 
> 4.1 kernel an apt-source get linux-image only turned up older 3.x kernels and 
> i could not find any sources in the raspbian repositories which is strange.
>
> It seems to me also that the pwm driver which i am after is also just fully 
> enabled by patches which have been seen on this list recently.  And against 
> what kernel tree are all these patches?

Generally, this list is for the upstream rpi kernel development.  As far
as I know, the downstream (github.com/raspberrypi/linux) tree manages
their development and bug reporting all on github.com.  I'm working on
bringing the two worlds closer together, but it's a long road.

My guess would be that you didn't specify the .dtb file in the
firmware's config.txt. The firmware is what loads and delivers it to the
kernel, and does some edits in the process.  The config.txt line would
look something like:

device_tree=bcm2709-rpi-2-b.dtb

(possibly under dtbs/kernelversion/, depending on how you installed)
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