linux-kernel - [PATCH v4 2/4] PCI: Move jailhouse's isolated function handling to pci_scan

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Date:   Fri, 22 Apr 2022 15:28:56 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, linux-pci@...r.kernel.org
Subject: [PATCH v4 2/4] PCI: Move jailhouse's isolated function handling to pci_scan_slot()

The special case of the jailhouse hypervisor passing through individual
PCI functions handles scanning for PCI functions even if function 0 does
not exist. Currently this is done with an extra loop duplicating the one
in pci_scan_slot(). By incorporating the check for jailhouse_paravirt()
into pci_scan_slot() we can instead do this as part of the normal
slot scan. Note that with the assignment of dev->multifunction gated by
fn > 0 we set dev->multifunction unconditionally for all functions if
function 0 is missing just as in the existing jailhouse loop.

The only functional change is that we now call
pcie_aspm_init_link_state() for these functions but this already
happened if function 0 was passed through and should not be a problem.

Cc: Jan Kiszka <jan.kiszka@...mens.com>
Link: https://lore.kernel.org/linux-pci/20220408224514.GA353445@bhelgaas/
Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
 drivers/pci/probe.c | 30 ++++++++++--------------------
 1 file changed, 10 insertions(+), 20 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 2000e9858f12..ce4e41a7d358 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2659,8 +2659,13 @@ int pci_scan_slot(struct pci_bus *bus, int devfn)
 			if (fn > 0)
 				dev->multifunction = 1;
 		} else if (fn == 0) {
-			/* function 0 is required */
-			break;
+			/*
+			 * function 0 is required unless we are running on
+			 * a hypervisor which passes through individual PCI
+			 * functions.
+			 */
+			if (!jailhouse_paravirt())
+				break;
 		}
 		fn = next_fn(bus, dev, fn);
 	} while (fn >= 0);
@@ -2859,29 +2864,14 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
 {
 	unsigned int used_buses, normal_bridges = 0, hotplug_bridges = 0;
 	unsigned int start = bus->busn_res.start;
-	unsigned int devfn, fn, cmax, max = start;
+	unsigned int devfn, cmax, max = start;
 	struct pci_dev *dev;
-	int nr_devs;
 
 	dev_dbg(&bus->dev, "scanning bus\n");
 
 	/* Go find them, Rover! */
-	for (devfn = 0; devfn < 256; devfn += 8) {
-		nr_devs = pci_scan_slot(bus, devfn);
-
-		/*
-		 * The Jailhouse hypervisor may pass individual functions of a
-		 * multi-function device to a guest without passing function 0.
-		 * Look for them as well.
-		 */
-		if (jailhouse_paravirt() && nr_devs == 0) {
-			for (fn = 1; fn < 8; fn++) {
-				dev = pci_scan_single_device(bus, devfn + fn);
-				if (dev)
-					dev->multifunction = 1;
-			}
-		}
-	}
+	for (devfn = 0; devfn < 256; devfn += 8)
+		pci_scan_slot(bus, devfn);
 
 	/* Reserve buses for SR-IOV capability */
 	used_buses = pci_iov_bus_range(bus);
-- 
2.32.0