RE: [PATCH v3] cxl: Add committed sysfs attribute to CXL decoder

[Dan Williams <dan.j.williams@intel.com>]

Dave Jiang wrote:
> This attribute allows cxl-cli to determine whether a decoder is
> actively participating in a region. This is only a snapshot of the
> state, and doesn't offer any protection or serialization against a
> concurrent disable-region operation.

A random thought occurred while realizing that the kernel uses a check
of:

    port->commit_end != -1

...to determine that a given port (switch or endpoint) has committed
decoders. If the goal here is to determine when it is safe to disable an
entire memdev maybe it is better to check all of the decoders at once at
the port level rather than one at a time. It is already the case that
CXL prevents decoders from being committed out of order so what do you
think of replacing decoderX.Y/committed with portX/decoders_committed,
where it just does:

    down_read(&cxl_region_rwsem);
    sysfs_emit("%d\n", port->commit_end + 1);
    up_read(&cxl_region_rwsem);

...and cxl-cli aborts destructive processes on that attribute being
non-zero.

Is there any use case for userspace to check for individual decoders
being committed? It can infer "decoder committed" from "decoder_id <
decoders_commited".