cxl/edac: Fix the min_scrub_cycle of a region miscalculation

JIRA: https://issues.redhat.com/browse/RHEL-107284

commit fdc9be9
Author: Li Ming <ming.li@zohomail.com>
Date:   Tue Jun 3 18:43:13 2025 +0800

    cxl/edac: Fix the min_scrub_cycle of a region miscalculation

    When trying to update the scrub_cycle value of a cxl region, which means
    updating the scrub_cycle value of each memdev under a cxl region. cxl
    driver needs to guarantee the new scrub_cycle value is greater than the
    min_scrub_cycle value of a memdev, otherwise the updating operation will
    fail(Per Table 8-223 in CXL r3.2 section 8.2.10.9.11.1).

    Current implementation logic of getting the min_scrub_cycle value of a
    cxl region is that getting the min_scrub_cycle value of each memdevs
    under the cxl region, then using the minimum min_scrub_cycle value as
    the region's min_scrub_cycle. Checking if the new scrub_cycle value is
    greater than this value. If yes, updating the new scrub_cycle value to
    each memdevs. The issue is that the new scrub_cycle value is possibly
    greater than the minimum min_scrub_cycle value of all memdevs but less
    than the maximum min_scrub_cycle value of all memdevs if memdevs have
    a different min_scrub_cycle value. The updating operation will always
    fail on these memdevs which have a greater min_scrub_cycle than the new
    scrub_cycle.

    The correct implementation logic is to get the maximum value of these
    memdevs' min_scrub_cycle, check if the new scrub_cycle value is greater
    than the value. If yes, the new scrub_cycle value is fit for the region.

    The change also impacts the result of
    cxl_patrol_scrub_get_min_scrub_cycle(), the interface returned the
    minimum min_scrub_cycle value among all memdevs under the region before
    the change. The interface will return the maximum min_scrub_cycle value
    among all memdevs under the region with the change.

    Signed-off-by: Li Ming <ming.li@zohomail.com>
    Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
    Reviewed-by: Dave Jiang <dave.jiang@intel.com>
    Reviewed-by: Shiju Jose <shiju.jose@huawei.com>
    Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
    Link: https://patch.msgid.link/20250603104314.25569-1-ming.li@zohomail.com
    Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Signed-off-by: John W. Linville <linville@redhat.com>

Author: John W. Linville

drivers/cxl/core/edac.c

@@ -102,10 +102,10 @@ static int cxl_scrub_get_attrbs(struct cxl_patrol_scrub_context *cxl_ps_ctx,
 				u8 *cap, u16 *cycle, u8 *flags, u8 *min_cycle)
 {
 	struct cxl_mailbox *cxl_mbox;
-	u8 min_scrub_cycle = U8_MAX;
 	struct cxl_region_params *p;
 	struct cxl_memdev *cxlmd;
 	struct cxl_region *cxlr;
+	u8 min_scrub_cycle = 0;
 	int i, ret;
 
 	if (!cxl_ps_ctx->cxlr) {
@@ -132,8 +132,12 @@ static int cxl_scrub_get_attrbs(struct cxl_patrol_scrub_context *cxl_ps_ctx,
 		if (ret)
 			return ret;
 
+		/*
+		 * The min_scrub_cycle of a region is the max of minimum scrub
+		 * cycles supported by memdevs that back the region.
+		 */
 		if (min_cycle)
-			min_scrub_cycle = min(*min_cycle, min_scrub_cycle);
+			min_scrub_cycle = max(*min_cycle, min_scrub_cycle);
 	}
 
 	if (min_cycle)