pci: Sync PCIe downstream port LNKSTA on read

The PCIe link speed and width between a downstream device and its
upstream port is negotiated on real hardware and susceptible to
dynamic changes due to signal issues and power management.  In the
emulated device case there is no real hardware link, but we still
might wish to have some consistency between endpoint and downstream
port via a virtual negotiation.  There is of course a real link for
assigned devices and this same virtual negotiation allows the
downstream port to match the endpoint, synchronizing on every read
to support underlying physical hardware dynamically adjusting the
link.

This negotiation is intentionally unidirectional for compatibility.
If the endpoint exceeds the capabilities of the downstream port or
there is no endpoint device, the downstream port reports negotiation
to its maximum speed and width, matching the previous case where
negotiation was absent.  De-tuning the endpoint to match a virtual
link doesn't seem to benefit anyone and is a condition we've thus
far reported without functional issues.

Note that PCI_EXP_LNKSTA is already ignored for migration
compatibility via pcie_cap_v1_fill().

Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Tested-by: Geoffrey McRae <geoff@hostfission.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 14 insertions, 0 deletions

diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index e6514bb..eb12fa1 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -737,6 +737,19 @@ static inline int pci_is_express(const PCIDevice *d)
     return d->cap_present & QEMU_PCI_CAP_EXPRESS;
 }
 
+static inline int pci_is_express_downstream_port(const PCIDevice *d)
+{
+    uint8_t type;
+
+    if (!pci_is_express(d) || !d->exp.exp_cap) {
+        return 0;
+    }
+
+    type = pcie_cap_get_type(d);
+
+    return type == PCI_EXP_TYPE_DOWNSTREAM || type == PCI_EXP_TYPE_ROOT_PORT;
+}
+
 static inline uint32_t pci_config_size(const PCIDevice *d)
 {
     return pci_is_express(d) ? PCIE_CONFIG_SPACE_SIZE : PCI_CONFIG_SPACE_SIZE;
diff --git a/include/hw/pci/pcie.h b/include/hw/pci/pcie.h
index b71e369..1976909 100644
--- a/include/hw/pci/pcie.h
+++ b/include/hw/pci/pcie.h
@@ -126,6 +126,7 @@ uint16_t pcie_find_capability(PCIDevice *dev, uint16_t cap_id);
 void pcie_add_capability(PCIDevice *dev,
                          uint16_t cap_id, uint8_t cap_ver,
                          uint16_t offset, uint16_t size);
+void pcie_sync_bridge_lnk(PCIDevice *dev);
 
 void pcie_ari_init(PCIDevice *dev, uint16_t offset, uint16_t nextfn);
 void pcie_dev_ser_num_init(PCIDevice *dev, uint16_t offset, uint64_t ser_num);