[PATCH] lmb: Reinstate access to memory above ram_top

[Casey Connolly]

On 09/02/2026 21:44, Marek Vasut wrote:
> On 2/9/26 7:45 PM, Casey Connolly wrote:
> 
> Hello Casey,
> 
>>> Which means, before we can really start switching boards to relocate to
>>> 64bit space, we need to find all these remaining 32bit limitation sites
>>> and fix them first. And to do that, we would need some way to force
>>> allocation from 32bit space for drivers which need that ... do we
>>> already have such a thing ? I couldn't find anything.
>>
>> For some (non-upstream) Qualcomm drivers we have just used lmb with
>> LMB_ALLOC_MAX and passed in 4GB as the max address, it would be nice to
>> have a wrapper function for this.
>>
>> Maybe this would just cause a whole bunch of other issues but perhaps it
>> would be easiest to have a config option to place the malloc arena in
>> 32-bit memory rather than always directly below U-Boot? Then again I
>> imagine this is something that has been bikeshed in the past...
> 
> Are those qualcomm devices suffering from 32bit DMA limitation too ?

Yeah, this is how we handle allocating the framebuffer for
not-yet-upstream display support.

Would it be possible to use SMMU TLBs to allow (most) 32-bit-only
peripherals to access 64-bit addresses?

> 
>> *casey grumbles something about making relocation optional and merging
>> the f/r init sequences for most boards*
> 
> Can you try CONFIG_SKIP_RELOCATE for your use case ?

That works fine, I'm mostly frustrated with the whole pre-reloc FDT
scanning/DM init, lack of dcache, etc... So pretty unrelated issues heh.

-- 
// Casey (she/her)