Re: Backporting commits for generating rpi dtb symbols to stable

From: Florian Fainelli
Date: Mon Jul 17 2023 - 06:38:57 EST



On 7/16/2023 9:51 PM, Pali Rohár wrote:
On Sunday 16 July 2023 21:08:38 Greg KH wrote:
On Sun, Jul 16, 2023 at 06:38:52PM +0200, Pali Rohár wrote:
On Sunday 16 July 2023 18:32:42 Greg KH wrote:
On Sun, Jul 16, 2023 at 06:24:44PM +0200, Pali Rohár wrote:
Hello,

I see that raspberry pi bootloader throws ton of warnings when supplied
DTB file does not contain /__symbols__/ node.

On RPI 1B rev1 it looks like this:

dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found
dterror: no symbols found

Bootloader also propagates these warnings to kernel via dtb property
chosen/user-warnings and they can be read by simple command:

$ cat /sys/firmware/devicetree/base/chosen/user-warnings
...

Upstream Linux kernel build process by default does not generate
/__symbols__/ node for DTB files, but DTB files provided by raspberrypi
foundation have them for a longer time.

I wanted to look at this issue, but I figured out that it is already
solved by just recent Aurelien's patches:

e925743edc0d ("arm: dts: bcm: Enable device-tree overlay support for RPi devices")
3cdba279c5e9 ("arm64: dts: broadcom: Enable device-tree overlay support for RPi devices")

My testing showed that /__symbols__/ node is required by rpi bootloader
for overlay support even when overlayed DTB file does not use any DTB
symbol (and reference everything via full node path). So seems that
/__symbols__/ node is crucial for rpi bootloader even when symbols from
them are not used at all.

So I would like to ask, would you consider backporting these two
raspberry pi specific patches to stable kernel trees? Upstream kernel
would get rid of those bootloader warnings and also allow users to use
overlayed dtbs...

What kernel tree(s) should these be applied to? What trees did you test
them for?

Also, adding dt-overlay support does not seem like a stable kernel fix,
as this isn't a bugfix from what I can tell, right?

thanks,

greg k-h

I wanted to discuss what do you think about it. As I wrote my motivation
was to understood and get rid of those warnings "dterror: no symbols
found" from bootloader when using DTB files from mainline kernel (as
opposite of the DTB files from rpi foundation). And fix for it was just
to generate DTB files from kernel via dtc's -@ parameter, same what are
doing those mentioned patches (but they describe different problem for
which is same fix). I thought that fixing those bootloader warnings is a
bugfix.

Why not just use the next kernel version instead? What's forcing you to
use an older stable kernel that didn't have dt-overlay support?

thanks,

greg k-h

Why not use the next kernel? It is pretty simple, next is the
development tree, not for production.

Maybe "next" should have not been taken as designating linux-next, but whichever kernel version you are currently using wait for 6.5 final and use it since it does contains Aurelien's commits.

And as I wrote in previous email,
I do not need here dt-overlay support. I wanted to get rid off that
warning messages.

The motivation does not seem appropriate to warrant a stable backport, besides as noted in the commit message including relocation information inflates the resulting .dtb files, which could be seen as a regression.
--
Florian

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