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

[Marek Vasut]

On 12/2/22 16:00, Miquel Raynal wrote:
> Hi Marek,

Hi,

> marex at denx.de wrote on Fri, 2 Dec 2022 15:31:40 +0100:
> 
>> 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.
> 
> I agree we should not proliferate incorrect DTs, so let's use a modern
> description then

Yes please !

> , with a controller and a child node which defines the
> chip.

But what if there is no chip connected to the controller node ?

If I understand the proposal here right (please correct me if I'm 
wrong), then:

1) This is the original, old, wrong binding:
&gpmi {
   #size-cells = <1>;
   ...
   partition at N { ... };
};


2) This is the newer, but still wrong binding:
&gpmi {
   #size-cells = <0>;
   ...
   partitions {
     partition at N { ... };
   };
};

3) This is the newest binding, what we want:
&gpmi {
   #size-cells = <0>;
   ...
   nand-chip {
     partitions {
       partition at N { ... };
     };
   };
};

But if there is no physical nand chip connected to the controller, would 
we end up with empty nand-chip node in DT, like this?
&gpmi {
   #size-cells = <X>;
   ...
   nand-chip { /* empty */ };
};
What would be the gpmi controller size cells (X) in that case, still 0, 
right ? So how does that help solve this problem, wouldn't U-Boot still 
populate the partitions directly under the gpmi node or into partitions 
sub-node ?

>> 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,
> 
> I am sorry to say so, but while warnings reported by the tools
> should be fixed, it's not because the tool does not scream at you that
> the description is valid. We are actively working on enhancing the
> schema so that "all" improper descriptions get warnings (see the series
> pointed earlier), but in no way this change makes the node compliant
> with modern bindings.
> 
> I'm not saying the fix is wrong, but let's be pragmatic, it currently
> leads to boot failures.

I fully agree that we do have a problem, and that it trickled into 
stable makes it even worse. Maybe I don't fully understand the thing 
with nand-chip proposal, see my question above, esp. the last part.

>> only to work around a problem induced by bootloader, is the right approach
>> here.
> 
> When a patch breaks a board and there is no straight fix, you revert
> it, then you think harder. That's what I am saying. This is a temporary
> solution.

Isn't this patch the straight fix, at least until the bootloader can be 
updated to generate the nand-chip node correctly ?

>> 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.
> 
> Please, you know this is not valid DT clean up. We've been decoupling
> controller and chip description since 2016. What I am proposing is a
> valid DT cleanup, not to the latest standard, but way closer than the
> current solution.

I think I really need one more explanation of the nand-chip part above.

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