Re: [PATCH v11 12/31] cxl/mem: Set up framework for handling DC Events

On Fri, Jun 26, 2026 at 02:54:43PM -0700, Dave Jiang wrote:
> 
> 
> On 6/25/26 4:04 AM, Anisa Su wrote:
> > From: Ira Weiny <[email protected]>
> > 
> > Adds the support for receiving DC event records but defers
> > the real add/release logic to subsequent commits. Simply refuse all
> > extents for DC_ADD and ack all DC_RELEASE events for now. Forced
> > release is currently unsupported.
> > 
> > In order, this commit adds the following:
> > 
> > 1. Learn about DC Event Records and how to respond to them
> > 
> > * cxl_mem_get_event_records() learns about the DC Event record.
> > Records of that type are routed to cxl_handle_dcd_event_records().
> > 
> > * cxl_handle_dcd_event_records() switches on event_type:
> > 	- DCD_ADD_CAPACITY     -> handle_add_event()
> > 	- DCD_RELEASE_CAPACITY -> cxl_rm_extent()
> > 	- DCD_FORCED_CAPACITY_RELEASE is logged and ignored (FM/device-only).
> > 
> > * cxl_send_dc_response() sends the reply mailbox commands
> > ADD_DC_RESPONSE / RELEASE_DC
> > 
> > 2. Add stubs for DC_ADD and DC_RELEASE logic
> > 
> > * handle_add_event() stages incoming extents onto
> > mds->add_ctx.pending_extents and, when More=0 closes the chain,
> > replies with an empty ADD_DC_RESPONSE — refusing all extents for now
> > 
> > * cxl_rm_extent() acks the release via memdev_release_extent() so the
> > device's view stays consistent; we can ack all releases because
> > we currently don't accept/use any extents offered.
> > 
> > 3. Structural setup for later commits:
> > 
> > * struct dc_extent, struct cxl_dc_tag_group, and pending_add_ctx
> > set up the stage for the real DC_ADD path, which will enforce
> > tag/grouping semantics
> > 
> > Based on an original patch by Navneet Singh.
> > 
> > Signed-off-by: Ira Weiny <[email protected]>
> > Signed-off-by: Anisa Su <[email protected]>
> 
> Just a minor comment below besides all the issues raised by sashiko
> 
Got it!

> 
> > 
> > +
[snip]

I also meant to ask in the last rev but I forgot: are these stub
comments useful or should I just get rid of them?

> > +/*
> > + * Stub: ack the release back to the device so it knows we are not
> > + * using the range.  A later commit replaces this with the real
> > + * teardown that walks the region's tag group and tears down the
> > + * member dc_extent devices.
> > + */
> > +static int cxl_rm_extent(struct cxl_memdev_state *mds,
> > +			 struct cxl_extent *extent)
> > +{
> > +	u64 start_dpa = le64_to_cpu(extent->start_dpa);
> > +	struct range dpa_range = {
> > +		.start = start_dpa,
> > +		.end = start_dpa + le64_to_cpu(extent->length) - 1,
> > +	};
> > +
> > +	memdev_release_extent(mds, &dpa_range);
> > +	return 0;
> > +}
> > +
> > +static char *cxl_dcd_evt_type_str(u8 type)
> 
> Should it return 'const char *' instead?
> 
Yes

> DJ
> 
Thanks,
Anisa

> > +{
> > +	switch (type) {
> > +	case DCD_ADD_CAPACITY:
> > +		return "add";
> > +	case DCD_RELEASE_CAPACITY:
> > +		return "release";
> > +	case DCD_FORCED_CAPACITY_RELEASE:
> > +		return "force release";
> > +	default:
> > +		break;
> > +	}
> > +
> > +	return "<unknown>";
> > +}
> > +
[snip]