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

[Dave Jiang <dave.jiang@intel.com>]

On 10/3/23 15:40, Dan Williams wrote:
> 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.

Seems reasonable. I'll rework the patch and the cxl cli code. 

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