[PATCH v1 0/3] fdt: Fix mtparts fixup

[Tom Rini]

On Mon, Jan 23, 2023 at 11:06:06AM +0100, Miquel Raynal wrote:
> Hi Tom,
> 
> trini at konsulko.com wrote on Fri, 13 Jan 2023 14:34:11 -0500:
> 
> > On Fri, Jan 13, 2023 at 07:45:44PM +0100, Francesco Dolcini wrote:
> > 
> > > From: Francesco Dolcini <francesco.dolcini at toradex.com>
> > > 
> > > Recently we had a boot regression on colibri-imx7 because of a cleanup change
> > > on Linux imx7.dtsi setting nand controller node #size-cells from 1 to 0.
> > > 
> > > Because of that Linux partition parser was no longer able to properly
> > > parse the OF partitions leading to a boot failure, the above change was
> > > reverted in the meantime as an immediate workaround, but some improvement
> > > is required on both Linux and U-Boot.
> > > 
> > > This change improve the U-Boot part of it, #size-cell is set to 1 when
> > > it has an invalid value. This has the limitation to work only with devices
> > > smaller than 4GiB. In general the suggestion from the Linux MTD maintainer would
> > > be to just deprecate using this U-Boot function and pass the MTD partitions
> > > from the command line, unless they are statically defined in the DTS file
> > > in the first place.
> > > 
> > > This series therefore convert colibri-imx6ull and colibri-imx7 to pass the
> > > partition list from the command line instead of fixing up the DT.
> > > 
> > > Link: https://lore.kernel.org/all/20221202071900.1143950-1-francesco@dolcini.it/
> > > Link: https://lore.kernel.org/all/Y4dgBTGNWpM6SQXI@francesco-nb.int.toradex.com/  
> > 
> > My higher level question / concern here is, is using one of the dts
> > partition schemes still valid / preferred, or should everyone now have
> > reverted to passing via the kernel command line?  If device tree still,
> > is mtd/partitions/fixed-partitions.yaml the one to follow or something
> > else?
> 
> I don't think we can "prefer" one mode over the other between cmdline
> and DTS. Both should work pretty well. Of course on the cmdline you can
> only define fixed partitions and many devices require more advanced
> parsers, which are only available through DTS, but for simple
> partitions, it works totally okay.

When both are present, which one is used?

> The only thing that I would like to avoid is the need to write code in
> the bootloaders to tweak the FDT in order to add partitions. That is
> clearly not needed, error prone, and do not follow evolution of the
> "standard", as we just discovered.

I'm not sure about this. Looking around in U-Boot today, I see two types
of cases. One of which, the colibri case, can clearly be not done and
either passed on the command line, or put in to the device tree as
there's nothing run-time related being tweaked here. That's a fine path
to take on those platforms and Francesco's patches should be updated to
remove the unused C code too from the board code.

But the other cases are doing something dynamic and run-time related.
There's the omap3 igep00x0 family (which yes, legacy) that is doing NAND
or oneNAND and adjusting things at run time.  I don't know how much
anyone has interest in those platforms at this point, nor exactly who to
contact (for Linux or U-Boot). There's also the stm32mp1 family doing
something that's very not obvious at first glance, so I've cc'd the
maintainers there.

-- 
Tom
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