[PATCH] i2c: sandbox: Avoid calling dev_read_*() if CONFIG_OF_PLATDATA=y

[Marek Vasut]

On 11/21/25 6:40 PM, Simon Glass wrote:

Hello Simon,

>>>>> - create a new VALID_OFFSET assumption (split out from VALID_DTB)
>>>>> which checks offsets in fdt_next_tag()
>>>>>
>>>>> The latter might be best. It would likely be very cheap in terms of
>>>>> code size. In fact, I should have thought of this at the time.
>>>> Wouldn't it be better to not misuse libfdt ?
>>>
>>> It actually isn't a misuse. It is perfectly OK to pass an invalid
>>> offset and libfdt has defined behaviour in that case, absent any
>>> 'assumptions' we force.
>>
>> It actually isn't OK to pass in invalid offset if we compile FDT with
>> disabled tree validity checks.
> 
> We are saying exactly the same thing, if you read both of the above :-)

What I wrote is, that it is NOT OK to pass invalid offset to libfdt IFF 
the DT validity checks are disabled. This is yes a misuse.

>>> Remember, in Linux these checks are enabled. We added the 'assume'
>>> thing to reduce code size. Here you have found a situation where it
>>> breaks stuff, so we should back off the assumption a bit.
>> U-Boot also has those checks enabled, SPL does not, and things break
>> when OF_PLATDATA is enabled and there is no valid node associated with
>> the udevice.
> 
> Right, so add SPL_OF_LIBFDT_ASSUME_MASK for SPL and check the code
> size. If it is too much, add a new level FDT_ASSUME_EXISTS before
> FDT_ASSUME_SANE and use that for the necessary checks (there will only
> be a few, from my reading of the code).
The SPL assumes the FDT is valid, and disables FDT validation in libfdt, 
to keep the code size low.

U-Boot does enable that validation in libfdt, and grows its size a bit 
because of that (and also because the DT might come from outside), but 
SPL can not do that (and control DT does not generally come from outside 
in SPL).

That is why these few fixes actually repair the misuse, instead of 
re-enabling the validation in libfdt.