[Qemu-devel] [PATCH 53/56] pcie: fix link active status bit migration

[Michael Roth <mdroth@linux.vnet.ibm.com>]

From: "Michael S. Tsirkin" <mst@redhat.com>

We changed link status register in pci express endpoint capability
over time. Specifically,

commit b2101eae63ea57b571cee4a9075a4287d24ba4a4 ("pcie: Set the "link
active" in the link status register") set data link layer link active
bit in this register without adding compatibility to old machine types.

When migrating from qemu 2.3 and older this affects xhci devices which
under machine type 2.0 and older have a pci express endpoint capability
even if they are on a pci bus.

Add compatibility flags to make this bit value match what it was under
2.3.

Additionally, to avoid breaking migration from qemu 2.3 and up,
suppress checking link status during migration: this seems sane
since hardware can change link status at any time.

https://bugzilla.redhat.com/show_bug.cgi?id=1352860

Reported-by: Gerd Hoffmann <kraxel@redhat.com>
Fixes: b2101eae63ea57b571cee4a9075a4287d24ba4a4
    ("pcie: Set the "link active" in the link status register")
Cc: qemu-stable@nongnu.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

(cherry picked from commit 6b4495401bdf442457b713b7e3994b465c55af35)
Conflicts:
	hw/pci/pcie.c

* removed functional dependency on 6383292

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 hw/pci/pci.c         |  2 ++
 hw/pci/pcie.c        | 15 ++++++++++++++-
 include/hw/compat.h  |  4 ++++
 include/hw/pci/pci.h |  3 +++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index bb605ef..616f04c 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -62,6 +62,8 @@ static Property pci_props[] = {
                     QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
     DEFINE_PROP_BIT("command_serr_enable", PCIDevice, cap_present,
                     QEMU_PCI_CAP_SERR_BITNR, true),
+    DEFINE_PROP_BIT("x-pcie-lnksta-dllla", PCIDevice, cap_present,
+                    QEMU_PCIE_LNKSTA_DLLLA_BITNR, true),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
index 728386a..c85b4f7 100644
--- a/hw/pci/pcie.c
+++ b/hw/pci/pcie.c
@@ -47,6 +47,7 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
 {
     int pos;
     uint8_t *exp_cap;
+    uint8_t *cmask;
 
     assert(pci_is_express(dev));
 
@@ -57,6 +58,7 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
     }
     dev->exp.exp_cap = pos;
     exp_cap = dev->config + pos;
+    cmask = dev->cmask + pos;
 
     /* capability register
        interrupt message number defaults to 0 */
@@ -80,7 +82,18 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
                  PCI_EXP_LNK_LS_25);
 
     pci_set_word(exp_cap + PCI_EXP_LNKSTA,
-                 PCI_EXP_LNK_MLW_1 | PCI_EXP_LNK_LS_25 |PCI_EXP_LNKSTA_DLLLA);
+                 PCI_EXP_LNK_MLW_1 | PCI_EXP_LNK_LS_25);
+
+    if (dev->cap_present & QEMU_PCIE_LNKSTA_DLLLA) {
+        pci_word_test_and_set_mask(exp_cap + PCI_EXP_LNKSTA,
+                                   PCI_EXP_LNKSTA_DLLLA);
+    }
+
+    /* We changed link status bits over time, and changing them across
+     * migrations is generally fine as hardware changes them too.
+     * Let's not bother checking.
+     */
+    pci_set_word(cmask + PCI_EXP_LNKSTA, 0);
 
     pci_set_long(exp_cap + PCI_EXP_DEVCAP2,
                  PCI_EXP_DEVCAP2_EFF | PCI_EXP_DEVCAP2_EETLPP);
diff --git a/include/hw/compat.h b/include/hw/compat.h
index a5dbbf8..81fc19b 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -73,6 +73,10 @@
         .driver   = "virtio-rng-pci",\
         .property = "any_layout",\
         .value    = "off",\
+    },{\
+        .driver   = TYPE_PCI_DEVICE,\
+        .property = "x-pcie-lnksta-dllla",\
+        .value    = "off",\
     },
 
 #define HW_COMPAT_2_2 \
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index ef6ba51..e7f2df5 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -173,6 +173,9 @@ enum {
     /* PCI Express capability - Power Controller Present */
 #define QEMU_PCIE_SLTCAP_PCP_BITNR 7
     QEMU_PCIE_SLTCAP_PCP = (1 << QEMU_PCIE_SLTCAP_PCP_BITNR),
+    /* Link active status in endpoint capability is always set */
+#define QEMU_PCIE_LNKSTA_DLLLA_BITNR 8
+    QEMU_PCIE_LNKSTA_DLLLA = (1 << QEMU_PCIE_LNKSTA_DLLLA_BITNR),
 };
 
 #define TYPE_PCI_DEVICE "pci-device"
-- 
1.9.1