Re: Re: [PATCH] cxl/mbox: Add the CXL 4.0 command return codes 001Fh and 0020h

[黄高彬 <huanggaobin23@semi.ac.cn>]

Hi Richard,

> Do we have users for them ? or potential users ?

I checked the related code, and the honest answer is no for both today.

001Fh is the code Perform Maintenance (opcode 0600h) returns when the input
parameters are transferred in parts and the parts arrive out of order --
Action = Initiate Transfer, Continue Transfer, End Transfer (CXL r4.0,
8.2.10.7).  Linux does issue Perform Maintenance: PPR and the sparing
operations in edac.c both go through cxl_perform_maintenance().  That helper
always transfers the parameters in a single command though -- it returns
-ENOMEM when they do not fit in the mailbox payload instead of chunking --
so the ordering condition cannot arise from the driver.  The multi-chunk
flow in the specification is described for the Built-In Self-Test test
parameters, and there is no BIST support in the driver.

0020h is only the return code of Request Abort Background Operation (opcode
0005h).  Linux does not issue that command either.

So neither code has a producer in the driver today.  Both are defined in the
command return code table (CXL r4.0 Table 8-208) that CMD_CMD_RC_TABLE
transcribes, and carrying them costs two lines and no behavior change: a
device that reports either already comes back as -ENXIO through the
unknown-code path, so what the entries buy is a name instead of "unknown
return code".

If the point is that a definition should arrive with the code that can
produce it, that is a fair position too.  I can withdraw this patch and
resend it together with chunked maintenance transfer support, or with abort
support, whichever is implemented first. 

Thanks,
Gaobin