Re: Backporting commits for generating rpi dtb symbols to stable

[Greg KH]

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