From: hshoexer <hshoexer@yerbouti.franken.de>
Subject: acpidmar(4): Store PCI domain in softc for segment mapping
To: tech@openbsd.org
Date: Tue, 28 Jul 2026 15:39:46 +0200

Hi,

with this change I store the PCI domain in the softc.  Later I use
that value when mapping domain to segment.  Instead of counting.

Also fall back to segment 0, when ACPI did not provide a segment.
This actually enforces use of the IOMMU.
    
While there:
 - tweak printf to use segment instead of PCI domain
 - use ACPI provided segment instead of hardcoded 0 in ivhd_showpage()

ok?

Take care,
HJ.

-----------------------------------------------------------------------------
diff --git a/sys/arch/amd64/pci/acpipci.c b/sys/arch/amd64/pci/acpipci.c
index e3121987654..e5e861662d7 100644
--- a/sys/arch/amd64/pci/acpipci.c
+++ b/sys/arch/amd64/pci/acpipci.c
@@ -66,6 +66,7 @@ struct acpipci_softc {
 	char		sc_memex_name[32];
 	int		sc_bus;
 	uint32_t	sc_seg;
+	int		sc_domain;
 };
 
 int	acpipci_match(struct device *, void *, void *);
@@ -97,15 +98,14 @@ int
 acpipci_domain_to_seg(int domain)
 {
 	struct acpipci_softc *sc;
-	int i, d = 0;
+	int i;
 
 	for (i = 0; i < acpipci_cd.cd_ndevs; i++) {
 		sc = (struct acpipci_softc *)acpipci_cd.cd_devs[i];
 		if (sc == NULL)
 			continue;
-		if (d == domain)
+		if (sc->sc_domain == domain)
 			return sc->sc_seg;
-		d++;
 	}
 
 	return -1;
@@ -147,6 +147,9 @@ acpipci_attach(struct device *parent, struct device *self, void *aux)
 	aml_evalinteger(sc->sc_acpi, sc->sc_node, "_SEG", 0, NULL, &seg);
 	sc->sc_seg = seg;
 
+	/* Assigned when the PCI bus attaches. */
+	sc->sc_domain = -1;
+
 	if (aml_evalname(sc->sc_acpi, sc->sc_node, "_CRS", 0, NULL, &res)) {
 		printf(": can't find resources\n");
 
@@ -210,6 +213,7 @@ acpipci_attach_bus(struct device *parent, struct acpipci_softc *sc)
 	pba.pba_pmemex = sc->sc_memex;
 	pba.pba_domain = pci_ndomains++;
 	pba.pba_bus = sc->sc_bus;
+	sc->sc_domain = pba.pba_domain;
 
 	/* Enable MSI in ACPI 2.0 and above, unless we're told not to. */
 	if (sc->sc_acpi->sc_fadt->hdr.revision >= 2 &&
diff --git a/sys/dev/acpi/acpidmar.c b/sys/dev/acpi/acpidmar.c
index 57b90ddb193..cf18265fd09 100644
--- a/sys/dev/acpi/acpidmar.c
+++ b/sys/dev/acpi/acpidmar.c
@@ -2581,9 +2581,8 @@ acpidmar_pci_hook(pci_chipset_tag_t pc, struct pci_attach_args *pa)
 
 	segment = acpipci_domain_to_seg(pa->pa_domain);
 	if (segment < 0) {
-		DPRINTF(1, "acpidmar: no ACPI segment for pci domain %d\n",
-		    pa->pa_domain);
-		return;
+		/* Fall back to segment 0. */
+		segment = 0;
 	}
 
 	/* Record PCI-PCI bridge forwarding windows */
@@ -2608,7 +2607,7 @@ acpidmar_pci_hook(pci_chipset_tag_t pc, struct pci_attach_args *pa)
 	    PCI_SUBCLASS(reg) == PCI_SUBCLASS_BRIDGE_ISA) {
 		/* For ISA Bridges, map 0-16Mb as 1:1 */
 		printf("dmar: %.4x:%.2x:%.2x.%x mapping ISA\n",
-		    pa->pa_domain, bus, dev, fun);
+		    segment, bus, dev, fun);
 		domain_map_pthru(dom, 0x00, 16*1024*1024);
 
 		/* Keep the identity mapped IOVA range out of the allocator */
@@ -2917,7 +2916,7 @@ ivhd_showpage(struct iommu_softc *iommu, int sid, paddr_t paddr)
 	if (show > 10)
 		return;
 	show++;
-	dom = acpidmar_pci_attach(acpidmar_sc, 0, sid, 0);
+	dom = acpidmar_pci_attach(acpidmar_sc, iommu->segment, sid, 0);
 	if (!dom)
 		return;
 	printf("DTE: %.8x %.8x %.8x %.8x %.8x %.8x %.8x %.8x\n",