[[RFC PATCH v1] 1/1] PCI: Add pci=nobbn to ignore ACPI _BBN method to override host bridge bus window

[Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>]

Add pci=nobbn kernel parameter.

Override the host bridge bus resource to [bus 00-ff] when specified.

Update documentation to reflect the above.

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 arch/x86/include/asm/pci_x86.h                  |  1 +
 arch/x86/pci/acpi.c                             | 11 +++++++++++
 arch/x86/pci/common.c                           |  3 +++
 4 files changed, 17 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cfe8c2b67..0333d9d63 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3432,6 +3432,8 @@
 				please report a bug.
 		nocrs		[X86] Ignore PCI host bridge windows from ACPI.
 				If you need to use this, please report a bug.
+		nobbn		[X86] Ignore PCI BIOS Bus Number from ACPI.
+				If you need to use this, please report a bug.
 		routeirq	Do IRQ routing for all PCI devices.
 				This is normally done in pci_enable_device(),
 				so this option is a temporary workaround
diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
index 73bb404f4..179cdd5d1 100644
--- a/arch/x86/include/asm/pci_x86.h
+++ b/arch/x86/include/asm/pci_x86.h
@@ -39,6 +39,7 @@ do {						\
 #define PCI_ROOT_NO_CRS		0x100000
 #define PCI_NOASSIGN_BARS	0x200000
 #define PCI_BIG_ROOT_WINDOW	0x400000
+#define PCI_ROOT_NO_BBN		0x800000
 
 extern unsigned int pci_probe;
 extern unsigned long pirq_table_addr;
diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 948656069..fc54a1f3c 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -20,6 +20,7 @@ struct pci_root_info {
 };
 
 static bool pci_use_crs = true;
+static bool pci_use_bbn = true;
 static bool pci_ignore_seg = false;
 
 static int __init set_use_crs(const struct dmi_system_id *id)
@@ -156,6 +157,8 @@ void __init pci_acpi_crs_quirks(void)
 	else if (pci_probe & PCI_USE__CRS)
 		pci_use_crs = true;
 
+	pci_use_bbn = !(pci_probe & PCI_ROOT_NO_BBN);
+
 	printk(KERN_INFO "PCI: %s host bridge windows from ACPI; "
 	       "if necessary, use \"pci=%s\" and report a bug\n",
 	       pci_use_crs ? "Using" : "Ignoring",
@@ -298,6 +301,14 @@ static int pci_acpi_root_prepare_resources(struct acpi_pci_root_info *ci)
 	struct resource_entry *entry, *tmp;
 	int status;
 
+	if (!pci_use_bbn){
+		dev_printk(KERN_DEBUG, &device->dev,
+			   "host bridge window %pR (ignored)\n",
+			   &ci->root->secondary);
+		ci->root->secondary.start = 0x00;
+		ci->root->secondary.end = 0xff;
+	}
+
 	status = acpi_pci_probe_root_resources(ci);
 	if (pci_use_crs) {
 		resource_list_for_each_entry_safe(entry, tmp, &ci->resources)
diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index 9acab6ac2..9183a999f 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -594,6 +594,9 @@ char *__init pcibios_setup(char *str)
 	} else if (!strcmp(str, "nocrs")) {
 		pci_probe |= PCI_ROOT_NO_CRS;
 		return NULL;
+	} else if (!strcmp(str, "nobbn")) {
+		pci_probe |= PCI_ROOT_NO_BBN;
+		return NULL;
 #ifdef CONFIG_PHYS_ADDR_T_64BIT
 	} else if (!strcmp(str, "big_root_window")) {
 		pci_probe |= PCI_BIG_ROOT_WINDOW;
-- 
2.24.0