[PATCH v1] mtd: parsers: ofpart: Fix parsing when size-cells is 0

[Francesco Dolcini]

Hello Miquel,

On Thu, Jan 05, 2023 at 12:33:34PM +0100, Miquel Raynal wrote:
> miquel.raynal at bootlin.com wrote on Mon, 2 Jan 2023 10:40:04 +0100:
> > francesco at dolcini.it wrote on Fri, 16 Dec 2022 17:30:18 +0100:
> > > On Fri, Dec 16, 2022 at 04:35:01PM +0100, Miquel Raynal wrote:  
> > > > marex at denx.de wrote on Fri, 16 Dec 2022 15:32:28 +0100:    
> > > > > The second part of the message, as far as I understand it, is
> > > > > "ignore problems this will cause to users of boards we do not know
> > > > > about, let them run into unbootable systems after some linux kernel
> > > > > update,     
> > > > 
> > > > Now you know what kernel update will break them, so you can prevent it
> > > > from happening. 
> > > > 
> > > > For boards without even a dtsi in the kernel, should we care?    
> > > 
> > > Would caring for those boards not be just exact the same as caring for
> > > some UEFI/ACPI mess for which no source code is normally available and
> > > nobody really known at which point the various vendors have forked their
> > > source code from some Intel or AMD or whatever reference code?  
> > 
> > I am sorry I don't know UEFI/ACPI well enough to discuss it.
> > 
> > > IMHO we should care for the multiple reason I have already written in my
> > > previous emails.
> > > 
> > > And honestly, just as a side comment, I would feel way more happy
> > > to know that the elevator control system in the elevator I use everyday
> > > or the chemical industrial plan HMI next to my home is running an up to
> > > date Linux system that is not affected by known security vulnerabilities
> > > and they did stop updating it just because there was some random bug
> > > preventing the updated kernel to boot and nobody had the time/skill to
> > > investigate and fix it. [1]  
> > 
> > The issue comes from a very specific U-Boot function that should have
> > never existed. I hope people working on chemical plants do not make
> > use of these and will not disregard the "your DT is broken there [...]"
> > warning we plan to add right before their updated board will fail. We
> > are not living people in the dark, I agreed for a warning, but I don't
> > think applying the proposed fix blindly is wise and future-proof.
> 
> Let's move forward with this. Let's assume my fears are baseless. We
> might consider the situation where someone tries to hide the partitions
> by setting #size-cell to 0 even wronger and too unlikely. Hopefully we
> will not break any other existing setups by applying an always-on fix.

Nice, good!

> I would still like to see U-Boot partitions handling evolve, at least:
> - fix #size-cells in fdt_fixup_mtd()
> - avoid the fdt_fixup_mtd() call from Collibri boards (ie. an example
>   that can be followed by the other users)

Fine, I can do it. 

However I am just not 100% sure about your proposal, I wonder if we
should just deprecate this function or we should fix it.
The exact end result will depend on the discussion with the U-Boot
folks, but I absolutely agree that the current situation needs to
change. I'll keep you in CC on those patches.

> On Linux side let's fix #size-cells like you proposed without filtering
> against a list of compatibles. We however need to improve the
> heuristics:
> - Do it only when there are partitions declared within a NAND
>   controller node.
> - Change the warning to avoid mentioning backward compatibility, just
>   mention this is utterly wrong and thus the value will be set to 1
>   instead of 0.
> - Mention in the comment above this only works on systems with <4GiB
>   chips.
> If you think about other conditions please feel free to add them.
> 
> Do you concur?
Yes, I do agree.

Side comment, I have been recently busy with other life AND work priorities
and this task was just idling on the bottom of my backlog. I do not see
the situation improving that much in the next few weeks.

Said that patches coming, I am committed to have this sorted out before
the next Linux Kernel merge window, for U-Boot the merge window opens in
3 days and I am already late, let's see, this might be as well
considered a fix that is fine for a late integration.

Francesco