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

[Gregory Price <gourry@gourry.net>]

On Wed, Apr 30, 2025 at 09:29:15AM +0800, Li Zhijian wrote:
> During kernel booting, CXL drivers will attempt to construct the CXL region
> according to the pre-programed(firmware provisioning) HDM decoders.
> 
> This construction process will fail for some reasons, in this case, the
> userspace cli like ndctl/cxl cannot destroy nor create regions upon the
> existing decoders.
> 
> Introuce a new flag CXL_DECODER_F_NEED_RESET tell the driver to reset
> the decoder during `cxl destroy-region regionN`, so that region can be
> create again after that.
> 

My best understanding of why this is disallowed is that firmware/bios
programmed decoders need to be locked because there is an assumption
that the platform programmed it that way *for a reason* - and that
changing the programming would break it (cause MCEs for other reasons,
etc).

So the appropriate solution here is for the platform vendor to fix their
firmware.

But I am not a platform people - so I will defer to them on whether my
understanding is correct.

~Gregory