cxl/core: Use guard() to drop goto pattern of cxl_dpa_alloc()

In cxl_dpa_alloc(), some checking and operations need to be protected by
a rwsem called cxl_dpa_rwsem, so there is a goto pattern in
cxl_dpa_alloc() to release the rwsem. The goto pattern can be optimized
by using guard() to hold the rwsem.

Creating a new function called __cxl_dpa_alloc() to include all checking
and operations needed to be protected by cxl_dpa_rwsem. Using
guard(rwsem_write()) to hold cxl_dpa_rwsem at the beginning of the new
function.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Li Ming <ming.li@zohomail.com>
Link: https://patch.msgid.link/20250221012453.126366-6-ming.li@zohomail.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Author: MingLi-4

drivers/cxl/core/hdm.c

@@ -442,29 +442,25 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
 	return 0;
 }
 
-int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
+static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
 {
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
 	resource_size_t free_ram_start, free_pmem_start;
-	struct cxl_port *port = cxled_to_port(cxled);
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct device *dev = &cxled->cxld.dev;
 	resource_size_t start, avail, skip;
 	struct resource *p, *last;
-	int rc;
 
-	down_write(&cxl_dpa_rwsem);
+	guard(rwsem_write)(&cxl_dpa_rwsem);
 	if (cxled->cxld.region) {
 		dev_dbg(dev, "decoder attached to %s\n",
 			dev_name(&cxled->cxld.region->dev));
-		rc = -EBUSY;
-		goto out;
+		return -EBUSY;
 	}
 
 	if (cxled->cxld.flags & CXL_DECODER_F_ENABLE) {
 		dev_dbg(dev, "decoder enabled\n");
-		rc = -EBUSY;
-		goto out;
+		return -EBUSY;
 	}
 
 	for (p = cxlds->ram_res.child, last = NULL; p; p = p->sibling)
@@ -504,21 +500,24 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
 		skip = skip_end - skip_start + 1;
 	} else {
 		dev_dbg(dev, "mode not set\n");
-		rc = -EINVAL;
-		goto out;
+		return -EINVAL;
 	}
 
 	if (size > avail) {
 		dev_dbg(dev, "%pa exceeds available %s capacity: %pa\n", &size,
 			cxl_decoder_mode_name(cxled->mode), &avail);
-		rc = -ENOSPC;
-		goto out;
+		return -ENOSPC;
 	}
 
-	rc = __cxl_dpa_reserve(cxled, start, size, skip);
-out:
-	up_write(&cxl_dpa_rwsem);
+	return __cxl_dpa_reserve(cxled, start, size, skip);
+}
+
+int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
+{
+	struct cxl_port *port = cxled_to_port(cxled);
+	int rc;
 
+	rc = __cxl_dpa_alloc(cxled, size);
 	if (rc)
 		return rc;