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Blame SOURCES/kvm-s390x-pci-Fix-primary-bus-number-for-PCI-bridges.patch

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From 160715e23b00c660f0dfee3f1bdc021f9693d222 Mon Sep 17 00:00:00 2001
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From: Cornelia Huck <cohuck@redhat.com>
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Date: Wed, 17 Apr 2019 13:57:36 +0100
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Subject: [PATCH 19/24] s390x/pci: Fix primary bus number for PCI bridges
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RH-Author: Cornelia Huck <cohuck@redhat.com>
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Message-id: <20190417135741.25297-20-cohuck@redhat.com>
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Patchwork-id: 85800
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O-Subject: [RHEL-8.1.0 qemu-kvm PATCH v2 19/24] s390x/pci: Fix primary bus number for PCI bridges
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Bugzilla: 1699070
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RH-Acked-by: David Hildenbrand <david@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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RH-Acked-by: Jens Freimann <jfreimann@redhat.com>
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From: David Hildenbrand <david@redhat.com>
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The primary bus number corresponds always to the bus number of the
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bus the bridge is attached to.
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Right now, if we have two bridges attached to the same bus (e.g. root
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bus) this is however not the case. The first bridge will have primary
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bus 0, the second bridge primary bus 1, which is wrong. Fix the assignment.
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While at it, drop setting the PCI_SUBORDINATE_BUS temporarily to 0xff.
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Setting it temporarily to that value (as discussed e.g. in [1]), is
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only relevant for a running system that probes the buses. The value is
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effectively unused for us just doing a DFS.
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Also add a comment why we have to reassign during every reset (which I
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found to be surprising.
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Please note that hotplugging of bridges is in general still broken, will
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be fixed next.
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[1] http://www.science.unitn.it/~fiorella/guidelinux/tlk/node76.html
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Reviewed-by: Thomas Huth <thuth@redhat.com>
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Signed-off-by: David Hildenbrand <david@redhat.com>
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Message-Id: <20190130155733.32742-2-david@redhat.com>
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Reviewed-by: Collin Walling <walling@linux.ibm.com>
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Signed-off-by: Cornelia Huck <cohuck@redhat.com>
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(cherry picked from commit d30a7507edf1ca23d33dbf00b25f5e49a7808492)
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Signed-off-by: Cornelia Huck <cohuck@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 hw/s390x/s390-pci-bus.c | 13 ++++++++-----
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 1 file changed, 8 insertions(+), 5 deletions(-)
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diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
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index 07a286a..309ad79 100644
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--- a/hw/s390x/s390-pci-bus.c
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+++ b/hw/s390x/s390-pci-bus.c
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@@ -900,7 +900,8 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
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         qbus_set_hotplug_handler(bus, DEVICE(s), errp);
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         if (dev->hotplugged) {
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-            pci_default_write_config(pdev, PCI_PRIMARY_BUS, s->bus_no, 1);
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+            pci_default_write_config(pdev, PCI_PRIMARY_BUS,
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+                                     pci_dev_bus_num(pdev), 1);
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             s->bus_no += 1;
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             pci_default_write_config(pdev, PCI_SECONDARY_BUS, s->bus_no, 1);
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             do {
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@@ -1053,8 +1054,6 @@ static void s390_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
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                                       void *opaque)
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 {
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     S390pciState *s = opaque;
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-    unsigned int primary = s->bus_no;
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-    unsigned int subordinate = 0xff;
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     PCIBus *sec_bus = NULL;
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     if ((pci_default_read_config(pdev, PCI_HEADER_TYPE, 1) !=
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@@ -1063,7 +1062,7 @@ static void s390_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
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     }
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     (s->bus_no)++;
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-    pci_default_write_config(pdev, PCI_PRIMARY_BUS, primary, 1);
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+    pci_default_write_config(pdev, PCI_PRIMARY_BUS, pci_dev_bus_num(pdev), 1);
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     pci_default_write_config(pdev, PCI_SECONDARY_BUS, s->bus_no, 1);
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     pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, s->bus_no, 1);
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@@ -1072,7 +1071,7 @@ static void s390_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
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         return;
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     }
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-    pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, subordinate, 1);
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+    /* Assign numbers to all child bridges. The last is the highest number. */
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     pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
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                         s390_pci_enumerate_bridge, s);
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     pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, s->bus_no, 1);
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@@ -1083,6 +1082,10 @@ static void s390_pcihost_reset(DeviceState *dev)
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     S390pciState *s = S390_PCI_HOST_BRIDGE(dev);
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     PCIBus *bus = s->parent_obj.bus;
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+    /*
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+     * When resetting a PCI bridge, the assigned numbers are set to 0. So
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+     * on every system reset, we also have to reassign numbers.
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+     */
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     s->bus_no = 0;
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     pci_for_each_device(bus, pci_bus_num(bus), s390_pci_enumerate_bridge, s);
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 }
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-- 
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1.8.3.1
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