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

[Marek Vasut]

On 12/2/22 16:49, Miquel Raynal wrote:
> Hi Marek,

Hi,

>> 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:
> 
> Good idea to summarize.
> 
>>
>> 1) This is the original, old, wrong binding:
>> &gpmi {
>>     #size-cells = <1>;
>>     ...
>>     partition at N { ... };
>> };
> 
> Yes.
> 
>>
>>
>> 2) This is the newer, but still wrong binding:
>> &gpmi {
>>     #size-cells = <0>;
>>     ...
>>     partitions {
>>       partition at N { ... };
>>     };
>> };
> 
> Well, this is wrong description, but it would work (for compat reasons,
> even though I don't think this is considered valid DT by the schemas).
> 
>>
>> 3) This is the newest binding, what we want:
>> &gpmi {
>>     #size-cells = <0>;
>>     ...
>>     nand-chip {
>>       partitions {
>>         partition at N { ... };
>>       };
>>     };
>> };
> 
> Yes
> 
>>
>> 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 */ };
>> };
> 
> Is this really a concern?

I don't know, maybe it is not.

> If there is no NAND chip, the controller
> should be disabled, no? I guess technically you could even use the
> status property in the nand-chip node...

Sure.

> However, it should not be empty, at the very least a reg property
> should indicate on which CS it is wired, as expected there:
> https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/tree/Documentation/devicetree/bindings/mtd/nand-chip.yaml?h=mtd/next

OK, I see your point. So basically this?

&gpmi {
   #size-cells = <1>;
   ...
   nand-chip at 0 {
     reg = <0>;
   };
};

btw. the GPMI NAND controller supports only one chipselect, so the reg 
in nand-chip node makes little sense.

> But, as nand-chip.yaml references mtd.yaml, you can as well use
> whatever is described here:
> https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/tree/Documentation/devicetree/bindings/mtd/mtd.yaml?h=mtd/next
> 
>> 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 ?
> 
> The commit that was pointed in the original fix clearly stated that the
> NAND chip node was targeted

I think this is another miscommunication here. The commit

753395ea1e45 ("ARM: dts: imx7: Fix NAND controller size-cells")

modifies the size-cells of the NAND controller. The nand-chip is not 
involved in this at all . In the examples above, it's the "&gpmi" node 
size-cells that is modified.

> , not the NAND controller node. I hope this
> is correctly supported in U-Boot though. So if there is a NAND chip
> subnode, I suppose U-Boot would try to create the partitions that are
> inside, or even in the sub "partitions" container.

My understanding is that U-Boot checks the nand-controller node 
size-cells, not the nand-chip{} or partitions{} subnode size-cells .

Francesco, can you please share the DT, including the U-Boot generated 
partitions, which is passed to Linux on Colibri MX7 ? I think that 
should make all confusion go away.

(or am I the only one who's still confused here?)