cxl: Clarify comment in spa_maps_hpa()

Update the comment in spa_maps_hpa() to clearly convey the construction
of extended linear cache.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/linux-cxl/68eea19c7e67e_2f899100a8@dwillia2-mobl4.notmuch/
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Link: https://patch.msgid.link/20251106170108.1468304-3-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Author: davejiang

drivers/cxl/core/region.c

@@ -851,9 +851,9 @@ static bool spa_maps_hpa(const struct cxl_region_params *p,
 		return false;
 
 	/*
-	 * If an extended linear cache region then the CXL range is assumed
-	 * to be fronted by the DRAM range in current known implementation.
-	 * This assumption will be made until a variant implementation exists.
+	 * The extended linear cache region is constructed by a 1:1 ratio
+	 * where the SPA maps equal amounts of DRAM and CXL HPA capacity with
+	 * CXL decoders at the high end of the SPA range.
 	 */
 	return p->res->start + p->cache_size == range->start &&
 		p->res->end == range->end;