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

[Marek Vasut]

On 12/2/22 15:05, Miquel Raynal wrote:
> Hi Francesco,

Hi,

[...]

> I still strongly disagree with the initial proposal but what I think we
> can do is:
> 
> 1. To prevent future breakages:
>    Fix fdt_fixup_mtdparts() in u-boot. This way newer U-Boot + any
>    kernel should work.
> 
> 2. To help tracking down situations like that:
>    Keep the warning in ofpart.c but continue to fail.
> 
> 3. To fix the current situation:
>     Immediately revert commit (and prevent it from being backported):
>     753395ea1e45 ("ARM: dts: imx7: Fix NAND controller size-cells")
>     This way your own boot flow is fixed in the short term.

Here I disagree, the fix is correct and I think we shouldn't proliferate 
incorrect DTs which don't match the binding document. Rather, if a 
bootloader generates incorrect (new) DT entries, I believe the driver 
should implement a fixup and warn user about this. PC does that as well 
with broken ACPI tables as far as I can tell.

I'm not convinced making a DT non-compliant with bindings again, only to 
work around a problem induced by bootloader, is the right approach here.

This would be setting a dangerous example, where anyone could request a 
DT fix to be reverted because their random bootloader does the wrong 
thing and with valid DT clean up, something broke.

> 4. There is no reason to partially fix a DT like what the above did
>     besides trying to avoid warnings emitted by the DT check tools.

Note that the 3. does not partially fix the DT, it fixes the node fully.

>     If
>     complying with modern bindings is a goal (and I think it should
>     be), then we can modernize this DT without breaking the boot flow:
>     Instead of only setting #size-cell = <0>, you can as well define
>     in your DT a subnode to define the NAND chip. NAND chips are not
>     supposed to have #size-cells properties, but in the past they did,
>     which means #address-cells and #size-cells are allowed (and marked
>     deprecated in the schema). So in practice, the dt-schema will not
>     warn you if they are there, which means you can still set
>     #size-cell = <1>.

I am really not convinced we should hack around this on the DT end and 
try to push some sort of convoluted workaround there, instead of fixing 
it on the driver side (and bootloader side, in the long run).

>     Please mind, the tools have been updated very recently to match
>     what I am describing above, so they will likely still report
>     errors until v6.2-rc1, see:
>     https://lore.kernel.org/linux-mtd/20221114090315.848208-1-miquel.raynal@bootlin.com/
> 
> Does this sound reasonable?

[...]