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 <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Reviewed-by: Shiju Jose <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Dave Jiang <[email protected]>

Author: MingLi-4

drivers/cxl/core/edac.c

@@ -103,10 +103,10 @@ 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) {
@@ -133,8 +133,12 @@ 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)