[1/2] cxl/region: Try to add a region resource to a soft reserved parent

Commit Message

Alison Schofield June 24, 2023, 1:24 a.m. UTC

From: Alison Schofield <[e-mail]>

During region autodiscovery, the region driver always inserts the
region resource as a child of the root decoder, a CXL WINDOW. It
has the effect of making a soft reserved resource, with an exactly
matching address range, a child of the region resource.

It looks like this in /proc/iomem:

2080000000-29dbfffffff : CXL Window 0
  2080000000-247fffffff : region0
    2080000000-247fffffff : Soft Reserved

Search for soft reserved resources that include the region resource,
and add the new region resource as a child of that found resource.
If a soft reserved resource is not found, insert to the root decoder
as usual.

With this change, it looks like this:

2080000000-29dbfffffff : CXL Window 0
  2080000000-247fffffff : Soft Reserved
    2080000000-247fffffff : region0

This odd parenting only occurs when the resources are an exact match.
When the region resource only uses part of a soft reserved resource,
the parenting appears more logical like this:

2080000000-29dbfffffff : CXL Window 0
  2080000000-287fffffff : Soft Reserved
    2080000000-247fffffff : region0

Aside from the more logical appearance, this change is in preparation
for further cleanup in region teardown. A follow-on patch intends to
find and free soft reserved resources upon region teardown.

Signed-off-by: Alison Schofield <[e-mail]>
---
 drivers/cxl/core/region.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

Patch

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index f822de44bee0..1769ea92bf3a 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2652,6 +2652,28 @@  static int match_region_by_range(struct device *dev, void *data)
 	return rc;
 }
 
+static int insert_resource_soft_reserved(struct resource *soft_res, void *arg)
+{
+	struct resource *parent, *new, *res = arg;
+	bool found = false;
+
+	parent = soft_res->parent;
+	if (!parent)
+		return 0;
+
+	/* Caller provides a copy of soft_res. Find the actual resource. */
+	for (new = parent->child; new; new = new->sibling) {
+		if (resource_contains(new, soft_res)) {
+			found = true;
+			break;
+		}
+	}
+	if (found)
+		return insert_resource(new, res) == 0;
+
+	return 0;
+}
+
 /* Establish an empty region covering the given HPA range */
 static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
 					   struct cxl_endpoint_decoder *cxled)
@@ -2662,7 +2684,7 @@  static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
 	struct cxl_region_params *p;
 	struct cxl_region *cxlr;
 	struct resource *res;
-	int rc;
+	int rc = 0;
 
 	do {
 		cxlr = __create_region(cxlrd, cxled->mode,
@@ -2698,7 +2720,13 @@  static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
 
 	*res = DEFINE_RES_MEM_NAMED(hpa->start, range_len(hpa),
 				    dev_name(&cxlr->dev));
-	rc = insert_resource(cxlrd->res, res);
+
+	/* Try inserting to a Soft Reserved parent, fallback to root decoder */
+	if (walk_iomem_res_desc(IORES_DESC_SOFT_RESERVED, 0,
+				res->start, res->end, res,
+				insert_resource_soft_reserved) != 1)
+		rc = insert_resource(cxlrd->res, res);
+
 	if (rc) {
 		/*
 		 * Platform-firmware may not have split resources like "System