[PATCH v4 4/6] cxl/region: Support mixed-granularity user created regions

User region creation currently requires an interleaving root to have
the same granularity as the region.

That rejects valid mixed-granularity layouts where the region
granularity is finer than the root granularity. A region granularity
coarser than the root remains invalid because it produces incorrect
DPA translations.

Allow a region granularity finer than an interleaving root and
continue to reject a coarser granularity. Validate the complete
ways/granularity relationship when the region endpoints are attached.

For example, CXL 4.0 Section 9.13.1.1 Table 9-7 describes a 6-way
region at IGB across three host bridges as a 3-way root interleave at
2 * IGB with a 2-way interleave at IGB below it.

Signed-off-by: Alison Schofield <[email protected]>
---
 drivers/cxl/core/region.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 637d1b60a570..4bbfb7cd7e01 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -571,15 +571,8 @@ static int set_interleave_granularity(struct cxl_region *cxlr, int val)
 	if (rc)
 		return rc;
 
-	/*
-	 * When the host-bridge is interleaved, disallow region granularity !=
-	 * root granularity. Regions with a granularity less than the root
-	 * interleave result in needing multiple endpoints to support a single
-	 * slot in the interleave (possible to support in the future). Regions
-	 * with a granularity greater than the root interleave result in invalid
-	 * DPA translations (invalid to support).
-	 */
-	if (cxld->interleave_ways > 1 && val != cxld->interleave_granularity)
+	/* Region granularity must not be coarser than an interleaving root's */
+	if (cxld->interleave_ways > 1 && val > cxld->interleave_granularity)
 		return -EINVAL;
 
 	lockdep_assert_held_write(&cxl_rwsem.region);
-- 
2.37.3