cxl/region: Handle endpoint decoders in cxl_region_find_decoder()

In preparation for adding a new caller of cxl_region_find_decoders()
teach it to find a decoder from a cxl_endpoint_decoder structure.

Combining switch and endpoint decoder lookup in one function prevents
code duplication in call sites.

Update the existing caller.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Tested-by: Wonjae Lee <wj28.lee@samsung.com>
Link: https://lore.kernel.org/r/79ae6d72978ef9f3ceec9722e1cb793820553c8e.1706736863.git.alison.schofield@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: AlisonSchofield

drivers/cxl/core/region.c

@@ -730,12 +730,17 @@ static int match_auto_decoder(struct device *dev, void *data)
 	return 0;
 }
 
-static struct cxl_decoder *cxl_region_find_decoder(struct cxl_port *port,
-						   struct cxl_region *cxlr)
+static struct cxl_decoder *
+cxl_region_find_decoder(struct cxl_port *port,
+			struct cxl_endpoint_decoder *cxled,
+			struct cxl_region *cxlr)
 {
 	struct device *dev;
 	int id = 0;
 
+	if (port == cxled_to_port(cxled))
+		return &cxled->cxld;
+
 	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags))
 		dev = device_find_child(&port->dev, &cxlr->params,
 					match_auto_decoder);
@@ -853,10 +858,7 @@ static int cxl_rr_alloc_decoder(struct cxl_port *port, struct cxl_region *cxlr,
 {
 	struct cxl_decoder *cxld;
 
-	if (port == cxled_to_port(cxled))
-		cxld = &cxled->cxld;
-	else
-		cxld = cxl_region_find_decoder(port, cxlr);
+	cxld = cxl_region_find_decoder(port, cxled, cxlr);
 	if (!cxld) {
 		dev_dbg(&cxlr->dev, "%s: no decoder available\n",
 			dev_name(&port->dev));