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

["Lucero Palau, Alejandro" <alejandro.lucero-palau@amd.com>]

On 14/10/2026 17:23, Dave Jiang wrote:
>
> 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?


I have to admit I'm a bit lost with hotplugging and CXL needs, and not 
real experience with hot plug devices at all, but in my mind hotplugging 
allows a great flexibility which is counterintuitive if you need to know 
before hand which devices are going to be hot plugged ..., regarding 
CXL, how a CFMWS can be created without having that information? Maybe 
there is something in the specs about this and I did not pay attention.


What do you think about my other concern below?


> 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.
>>
>>