linux-kernel - [PATCH v3 2/4] PCI: Move jailhouse's isolated function handling to pci_scan

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Date:   Tue, 19 Apr 2022 12:28:01 +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 v3 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 next_fn() we can instead do this as part of the normal
pci_scan_slot(). 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.

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 | 28 +++++++---------------------
 1 file changed, 7 insertions(+), 21 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 389aa1f9cb2c..a1e8f1e14c3d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2602,10 +2602,11 @@ static int next_fn(struct pci_bus *bus, struct pci_dev *dev, int fn)
 	if (dev && !dev->multifunction)
 		return -ENODEV;
 	/*
-	 * A function 0 is required but multifunction devices may
-	 * be non-contiguous so dev can be NULL otherwise.
+	 * Usually a function 0 is required but the jailhouse hypervisor may
+	 * pass individual functions. For non-contiguous multifunction devices
+	 * some functions may also be missing.
 	 */
-	if (!fn && !dev)
+	if (!fn && !dev && !jailhouse_paravirt())
 		return -ENODEV;
 	return (fn <= 6) ? fn + 1 : -ENODEV;
 }
@@ -2855,29 +2856,14 @@ 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