Re: [RFC PATCH] cxl: Allow reprogramming misconfigured hdm decoders

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

On 30/04/2025 16:42, Alejandro Lucero Palau wrote:
>>
>> Hi Gregory,
>>
>> Thank you for the feedback. Based on current CXL driver behavior, user-space tools
>> can indeed reprogram firmware-provisioned HDM decoders in practice.
>>
>> For example, after a successful boot, one may destroy the auto-constructed region
>> via cxl destroy-region and create a new different region.
>> This indicates that the kernel does not inherently lock down these decoders.
>>
>> As for the locking rationale you mentioned, platform vendors might enforce their policies
>> through mechanisms like the *Lock-On-Commit* in CXL HDM Decoder n Control Register
>>
>> While platform vendors may have valid considerations (as you noted), from a driver and
>> end-user perspective, depending solely on firmware updates to fix transient failures
>> is not smooth sometimes 🙂.
>>
> 
> Hi Zhijan,
> 
> 
>  From my current effort trying to get a Type2 device properly initialized by the kernel after the BIOS/platform firmware doing whatever it needs to do, I really think we should have a wider discussion regarding this sync, and maybe to have first something from the kernel expectation of what the BIOS should and should not do.
> 
> 
> If this makes sense, I could work on a initial draft about the outline or points to discuss about this.
> 

Hi Alejandro,

Thanks for sharing this concrete pain point. Your experience highlights a critical gap in
"defining clear handoff protocols between firmware and the kernel" for CXL device initialization.
I agree that we need a community-driven effort to establish these expectations.


I’m happy to see your draft or thread for deeper discussion.

Best,
Zhijian


> 
> Thank you