Merge: cxl: core/region - ignore interleave granularity when ways=1

MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-10/-/merge_requests/285

When validating decoder IW/IG when setting up regions, the granularity is irrelevant when iw=1 - all accesses will always route to the only target anyway - so all ig values are "correct". Loosen the requirement that ig = (parent_iw * parent_ig) when iw=1.

On some Zen5 platforms, the platform BIOS specifies a 256-byte interleave granularity window for host bridges when there is only one target downstream. This leads to Linux rejecting the configuration of a region with a x2 root with two x1 hostbridges.

Decoder Programming: root - iw:2 ig:256 hb1 - iw:1 ig:256 (Linux expects 512) hb2 - iw:1 ig:256 (Linux expects 512) ep1 - iw:2 ig:256 ep2 - iw:2 ig:256

This change allows all decoders downstream of a passthrough decoder to also be configured as passthrough (iw:1 ig:X), but still disallows downstream decoders from applying subsequent interleaves.

e.g. in the above example if there was another decoder south of hb1 attempting to interleave 2 endpoints - Linux would enforce hb1.ig=512 because the southern decoder would have iw:2 and require ig=pig*piw.
Approved Development Ticket(s)

JIRA: https://issues.redhat.com/browse/RHEL-107880

Resolves: RHEL-107880

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

Approved-by: Tony Camuso <tcamuso@redhat.com>
Approved-by: Charles Mirabile <cmirabil@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>
Approved-by: Myron Stowe <mstowe@redhat.com>

Merged-by: Julio Faracco <jfaracco@redhat.com>

Author: jcfaracco

drivers/cxl/core/region.c

@@ -1423,7 +1423,7 @@ static int cxl_port_setup_targets(struct cxl_port *port,
 
 	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags)) {
 		if (cxld->interleave_ways != iw ||
-		    cxld->interleave_granularity != ig ||
+		    (iw > 1 && cxld->interleave_granularity != ig) ||
 		    cxld->hpa_range.start != p->res->start ||
 		    cxld->hpa_range.end != p->res->end ||
 		    ((cxld->flags & CXL_DECODER_F_ENABLE) == 0)) {