[PATCH v6 1/3] PCI: Cache bridge firmware secondary bus number

[Mario Limonciello <mario.limonciello@amd.com>]

Bridge scans are split into two passes when bus numbers need reassigning.
Save the firmware secondary bus number on the bridge pci_dev during pass
0, before the bridge is disabled, and keep it for pass 1 so devices
discovered there can read the original bus number via their upstream
bridge.

Guard the cached value with a validity flag so later rescans do not
overwrite it with the renumbered runtime value. Ignore unconfigured
secondaries and remember that pass 0 has already run so we do not
record runtime-assigned numbers on subsequent rescans.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/pci/probe.c | 16 ++++++++++++++--
 include/linux/pci.h |  4 ++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 27008e2ea5afc..f20a4b8f7a23b 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -505,14 +505,26 @@ static void pci_read_bridge_mmio_pref(struct pci_dev *dev, struct resource *res,
 static void pci_read_bridge_windows(struct pci_dev *bridge)
 {
 	u32 buses;
+	u8 secondary;
+	u8 subordinate;
 	u16 io;
 	u32 pmem, tmp;
 	struct resource res;
 
 	pci_read_config_dword(bridge, PCI_PRIMARY_BUS, &buses);
 	res.flags = IORESOURCE_BUS;
-	res.start = FIELD_GET(PCI_SECONDARY_BUS_MASK, buses);
-	res.end = FIELD_GET(PCI_SUBORDINATE_BUS_MASK, buses);
+	secondary = FIELD_GET(PCI_SECONDARY_BUS_MASK, buses);
+	subordinate = FIELD_GET(PCI_SUBORDINATE_BUS_MASK, buses);
+	res.start = secondary;
+	res.end = subordinate;
+
+	if (!bridge->fw_sec_bus_sampled) {
+		bridge->fw_sec_bus_sampled = true;
+		if (secondary > 0 && secondary < 0xff) {
+			bridge->fw_sec_busnr = secondary;
+			bridge->fw_sec_bus_valid = true;
+		}
+	}
 	pci_info(bridge, "PCI bridge to %pR%s\n", &res,
 		 bridge->transparent ? " (subtractive decode)" : "");
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 5ffcf5ce8c966..045157488b8e7 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -363,6 +363,8 @@ struct pci_dev {
 	struct pci_slot	*slot;		/* Physical slot this device is in */
 
 	unsigned int	devfn;		/* Encoded device & function index */
+	/* Firmware secondary bus number saved across bridge scan passes */
+	unsigned char	fw_sec_busnr;
 	unsigned short	vendor;
 	unsigned short	device;
 	unsigned short	subsystem_vendor;
@@ -414,6 +416,8 @@ struct pci_dev {
 	unsigned int	pme_poll:1;	/* Poll device's PME status bit */
 	unsigned int	pinned:1;	/* Whether this dev is pinned */
 	unsigned int	config_rrs_sv:1; /* Config RRS software visibility */
+	unsigned int	fw_sec_bus_valid:1; /* Firmware secondary bus number usable */
+	unsigned int	fw_sec_bus_sampled:1; /* Firmware secondary bus number captured */
 	unsigned int	imm_ready:1;	/* Supports Immediate Readiness */
 	unsigned int	d1_support:1;	/* Low power state D1 is supported */
 	unsigned int	d2_support:1;	/* Low power state D2 is supported */

-- 
2.43.0