[PATCH] pci: fix broadcom secondary bus reset handling

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

After a link reset, the Broadcom / LSI PEX890xx PCIe Gen 5 Switch in synth
mode will temporarily insert a fake place-holder device, 1000 02b2, before
the link is actually active for the expected downstream device. Confirm
the device's identifier matches what we expect before moving forward.
Otherwise, the pciehp driver may unmask hotplug notifications before
the link is actually active, which triggers an undesired device removal.

Cc: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Cc: Peter Delevoryas <pdel@meta.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/pci/pci.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e5f243dd42884..4dc00f7411a94 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1255,6 +1255,7 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 	int delay = 1;
 	bool retrain = false;
 	struct pci_dev *bridge;
+	u32 vid = dev->vendor | dev->device << 16;
 
 	if (pci_is_pcie(dev)) {
 		bridge = pci_upstream_bridge(dev);
@@ -1268,17 +1269,22 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 	 * responding to them with CRS completions.  The Root Port will
 	 * generally synthesize ~0 (PCI_ERROR_RESPONSE) data to complete
 	 * the read (except when CRS SV is enabled and the read was for the
-	 * Vendor ID; in that case it synthesizes 0x0001 data).
+	 * Vendor ID; in that case it synthesizes 0x0001 data, or if the device
+	 * is downstream a Broadcom switch, which syntesizes a fake device)
 	 *
 	 * Wait for the device to return a non-CRS completion.  Read the
-	 * Command register instead of Vendor ID so we don't have to
-	 * contend with the CRS SV value.
+	 * Command register instead of Vendor ID so we don't have to contend
+	 * with the CRS SV value. But, also read the Vendor and Device ID's
+	 * to defeat Broadcom switch's placeholder device.
 	 */
 	for (;;) {
-		u32 id;
+		u32 id, l;
 
+		pci_read_config_dword(dev, PCI_VENDOR_ID, &l);
 		pci_read_config_dword(dev, PCI_COMMAND, &id);
-		if (!PCI_POSSIBLE_ERROR(id))
+
+		if (!PCI_POSSIBLE_ERROR(id) && !PCI_POSSIBLE_ERROR(l) &&
+		    l == vid)
 			break;
 
 		if (delay > timeout) {
-- 
2.43.0