Re: [RFC PATCH v2 0/3] cxl: Provide explicit RAM region creation for Type-2 providers

[Dave Jiang]

On 10/14/26 8:34 AM, Lucero Palau, Alejandro wrote:
> 
> On 07/10/2026 10:05, Richard Cheng wrote:
>> A Type-2 provider uses devm_cxl_probe_mem() to register its memdev
>> and obtain an HPA range. This requires an existing committed region,
>> so registration fails when firmware has not configured one.
>>
>> Firmware may provide a suitable CFMWS window without programming a
>> region.
> 
> 
> Hi Richard,
> 
> 
> FWIW, I unsuccessfully  tried to explain this possibility to "BIOS people". The fact is, nowadays for AMD and I think for Intel as well, if there is no CXL device detected with CXL.mem enabled, the BIOS will neither set HDMs  nor there will be a CFMWS.


Hmmmm....don't they have to reserve CFMWS for hotplug?

DJ

> 
> 
> 
>> Hot-added devices can have the same requirement. A provider
>> needs its endpoint topology established before deciding when to
>> create a region and how much memory to map.
> 
> 
> Another unsuccessfully discussion was to avoid BIOS setting HDMs at hotplug time as this could race with host dynamic regions creation.
> 
> 
> I'm commenting these two things here for maybe having a community/kernel discussion with the goal of defining what BIOSes should do and mostly what they should not do if they want to be compatible with kernel expectations.
> 
>