linux-kernel - Re: Backporting commits for generating rpi dtb symbols to stable

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Message-ID: <20230716163852.jnd4u4ylvifgmpby@pali>
Date:   Sun, 16 Jul 2023 18:38:52 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Greg KH <greg@...ah.com>
Cc:     Aurelien Jarno <aurelien@...el32.net>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Backporting commits for generating rpi dtb symbols to stable

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.