cxl/region: Verify target positions using the ordered target list

When a root decoder is configured the interleave target list is read
from the BIOS populated CFMWS structure. Per the CXL spec 3.1 Table
9-22 the target list is in interleave order. The CXL driver populates
its decoder target list in the same order and stores it in 'struct
cxl_switch_decoder' field "@target: active ordered target list in
current decoder configuration"

Given the promise of an ordered list, the driver can stop duplicating
the work of BIOS and simply check target positions against the ordered
list during region configuration.

The simplified check against the ordered list is presented here.
A follow-on patch will remove the unused code.

For Modulo arithmetic this is not a fix, only a simplification.
For XOR arithmetic this is a fix for HB IW of 3,6,12.

Fixes: f9db85bf ("cxl/acpi: Support CXL XOR Interleave Math (CXIMS)")
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://patch.msgid.link/35d08d3aba08fee0f9b86ab1cef0c25116ca8a55.1719980933.git.alison.schofield@intel.comSigned-off-by: Dave Jiang <dave.jiang@intel.com>

drivers/cxl/core/region.c

@@ -1559,10 +1559,13 @@ static int cxl_region_attach_position(struct cxl_region *cxlr,
 				      const struct cxl_dport *dport, int pos)
 {
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct cxl_switch_decoder *cxlsd = &cxlrd->cxlsd;
+	struct cxl_decoder *cxld = &cxlsd->cxld;
+	int iw = cxld->interleave_ways;
 	struct cxl_port *iter;
 	int rc;
 
-	if (cxlrd->calc_hb(cxlrd, pos) != dport) {
+	if (dport != cxlrd->cxlsd.target[pos % iw]) {
 		dev_dbg(&cxlr->dev, "%s:%s invalid target position for %s\n",
 			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
 			dev_name(&cxlrd->cxlsd.cxld.dev));