Disabling the CXL regions ahead of a Secondary Bus Reset needs the set of
regions with a member endpoint below the Port being reset.

Add cxl_sbr_collect_regions() to walk the CXL port that owns the Downstream
Port and return every region with an endpoint below it, and
cxl_sbr_put_regions() to release the set.

Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
---
 drivers/cxl/core/core.h      |  2 ++
 drivers/cxl/core/dport_sbr.c | 66 ++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
index ac55f9e8160e..077a2af9cf0c 100644
--- a/drivers/cxl/core/core.h
+++ b/drivers/cxl/core/core.h
@@ -60,6 +60,8 @@ int cxl_region_invalidate_memregion(struct cxl_region *cxlr);
 int cxl_region_disable(struct cxl_region *cxlr);
 void cxl_region_enable(struct cxl_region *cxlr);
 struct pci_dev;
+int cxl_sbr_collect_regions(struct pci_dev *dport_pci, struct xarray *regions);
+void cxl_sbr_put_regions(struct xarray *regions);
 void cxl_sbr_recommit_decoders(struct pci_dev *dport_pci,
 			       struct xarray *hdm_state);
 
diff --git a/drivers/cxl/core/dport_sbr.c b/drivers/cxl/core/dport_sbr.c
index 0f398ab0d3a4..233499bc1fad 100644
--- a/drivers/cxl/core/dport_sbr.c
+++ b/drivers/cxl/core/dport_sbr.c
@@ -85,6 +85,72 @@ void cxl_region_enable(struct cxl_region *cxlr)
 		__func__, p->res, p->interleave_ways, p->interleave_granularity);
 }
 
+/*
+ * Collect the regions with a member endpoint routed through @dport_pci, the
+ * CXL Downstream Port about to be reset. cxl_rwsem.region keeps the topology
+ * stable for the duration of the walk only. Each collected region is pinned
+ * with get_device() so the object survives after the lock is dropped, since
+ * cxl_region_disable()/cxl_region_enable() run with the rwsem released (they
+ * unbind and rebind the region driver). Hence snapshot the set first.
+ */
+int cxl_sbr_collect_regions(struct pci_dev *dport_pci,
+			    struct xarray *regions)
+{
+	struct cxl_region_ref *cxl_rr;
+	struct cxl_dport *dport;
+	unsigned long index;
+	int count = 0;
+	int rc;
+
+	struct cxl_port *port __free(put_cxl_port) =
+		find_cxl_port(&dport_pci->dev, &dport);
+	if (!port) {
+		pci_dbg(dport_pci, "no CXL port found for reset dport\n");
+		return 0;
+	}
+
+	guard(rwsem_read)(&cxl_rwsem.region);
+	xa_for_each(&port->regions, index, cxl_rr) {
+		struct cxl_region *cxlr = cxl_rr->region;
+		struct cxl_ep *ep;
+		unsigned long ep_index;
+
+		/* Skip unless a region endpoint sits below the reset dport. */
+		xa_for_each(&cxl_rr->endpoints, ep_index, ep)
+			if (ep->dport == dport)
+				break;
+		if (!ep) {
+			dev_dbg(&cxlr->dev, "%s: no endpoint below %s, region excluded\n",
+				__func__, dev_name(dport->dport_dev));
+			continue;
+		}
+
+		get_device(&cxlr->dev);
+		rc = xa_insert(regions, (unsigned long)cxlr, cxlr, GFP_KERNEL);
+		if (rc) {
+			put_device(&cxlr->dev);
+			return rc;
+		}
+		dev_dbg(&cxlr->dev, "%s: endpoint below %s, region collected\n",
+			__func__, dev_name(dport->dport_dev));
+		count++;
+	}
+
+	dev_dbg(&port->dev, "%d region(s) routed through %s\n", count,
+		dev_name(dport->dport_dev));
+	return 0;
+}
+
+void cxl_sbr_put_regions(struct xarray *regions)
+{
+	struct cxl_region *cxlr;
+	unsigned long index;
+
+	xa_for_each(regions, index, cxlr)
+		put_device(&cxlr->dev);
+	xa_destroy(regions);
+}
+
 /*
  * The reset cleared the HDM Decoder registers of every CXL component below
  * @dport_pci, so restore them from the settings the driver holds and from
-- 
2.55.0