[PATCH] [RFC] lmb: Optionally limit available memory to 4 GiB on limited systems

[Marek Vasut]

On 6/3/26 1:41 PM, Peter Robinson wrote:

[...]

>>>>>>> +             if (size) {
>>>>>>>                         lmb_add(bd->bi_dram[i].start, size);
>>>>>>> +                     if (IS_ENABLED(CONFIG_LMB_LIMIT_DMA_BELOW_4G))
>>>>>>
>>>>>> This conditional should be inverted.
>>>>>>
>>>>>> Peter Robinson , can you test this change on RPi ?
>>>>>
>>>>> That doesn't fix the problem for me on a RPi4 4GB or a RPi5 8Gb.
>>>> Did you invert the if (IS_ENABLED...) conditional ?
>>>>
>>>> Was CONFIG_LMB_LIMIT_DMA_BELOW_4G enabled in your config (maybe the
>>>> Kconfig entry "default y" part needs to be tweaked to cover these devices?)
>>>>
>>>> If both conditions are met, that should behave like the old code.
>>>
>>> I dropped my revert and applied the patch, checked the new config
>>> option was in the generated .config (I mean you could test that with a
>>> "make rpi_arm64_defconfig" and checking the output).
>>
>> You need to invert the logic of IS_ENABLED() for this patch to work.
>> Marek obviously missed a !
> 
> Ah, I missed that bit in grabbing the patch, it seems to work on the
> RPi4 4Gb, not tested a RPi5 yet.

Lemme send an actual fixed up patch then ...