[libvirt] [PATCH 4/8] Allow PM reset on multi-function PCI devices

[Mark McLoughlin]

It turns out that a PCI Power Management reset only affects individual
functions, and not the whole device.

The PCI Power Management spec talks about resetting the 'device' rather
than the 'function', but Intel's Dexuan Cui informs me that it is
actually a per-function reset.

Also, Yu Zhao has added pci_pm_reset() to the kernel, and it doesn't
reject multi-function devices, so it must be true! :-)

(A side issue is that we could defer the PM reset to the kernel if we
could detect that the kernel has PM reset support, but barring version
number checks we don't have a way to detect that support)

* src/pci.c: remove the pciDeviceContainsOtherFunctions() check from
  pciTryPowerManagementReset() and prefer PM reset over bus reset
  where both are available

Cc: Cui, Dexuan <dexuan.cui at intel.com>
Cc: Yu Zhao <yu.zhao at intel.com>
---
 src/pci.c |   48 +++++++++---------------------------------------
 1 files changed, 9 insertions(+), 39 deletions(-)

diff --git a/src/pci.c b/src/pci.c
index 2dc2e1c..11b3e8b 100644
--- a/src/pci.c
+++ b/src/pci.c
@@ -402,29 +402,6 @@ pciBusContainsOtherDevices(virConnectPtr conn, pciDevice *dev)
     return 1;
 }
 
-/* Any other functions on this device ? */
-static int
-pciSharesDevice(pciDevice *a, pciDevice *b)
-{
-    return
-        a->domain == b->domain &&
-        a->bus == b->bus &&
-        a->slot == b->slot &&
-        a->function != b->function;
-}
-
-static int
-pciDeviceContainsOtherFunctions(virConnectPtr conn, pciDevice *dev)
-{
-    pciDevice *matched = NULL;
-    if (pciIterDevices(conn, pciSharesDevice, dev, &matched) < 0)
-        return 1;
-    if (!matched)
-        return 0;
-    pciFreeDevice(conn, matched);
-    return 1;
-}
-
 /* Is @a the parent of @b ? */
 static int
 pciIsParent(pciDevice *a, pciDevice *b)
@@ -529,7 +506,7 @@ out:
  * above we require the device supports a full internal reset.
  */
 static int
-pciTryPowerManagementReset(virConnectPtr conn, pciDevice *dev)
+pciTryPowerManagementReset(virConnectPtr conn ATTRIBUTE_UNUSED, pciDevice *dev)
 {
     uint8_t config_space[PCI_CONF_LEN];
     uint32_t ctl;
@@ -537,16 +514,6 @@ pciTryPowerManagementReset(virConnectPtr conn, pciDevice *dev)
     if (!dev->pci_pm_cap_pos)
         return -1;
 
-    /* For now, we just refuse to do a power management reset
-     * if there are other functions on this device.
-     * In future, we could allow it so long as those functions
-     * are not in use by the host or other guests.
-     */
-    if (pciDeviceContainsOtherFunctions(conn, dev)) {
-        VIR_WARN("%s contains other functions, not resetting", dev->name);
-        return -1;
-    }
-
     /* Save and restore the device's config space. */
     if (pciRead(dev, 0, &config_space[0], PCI_CONF_LEN) < 0) {
         VIR_WARN("Failed to save PCI config space for %s", dev->name);
@@ -604,14 +571,17 @@ pciResetDevice(virConnectPtr conn, pciDevice *dev)
     if (dev->has_flr)
         return 0;
 
+    /* If the device supports PCI power management reset,
+     * that's the next best thing because it only resets
+     * the function, not the whole device.
+     */
+    if (dev->has_pm_reset)
+        ret = pciTryPowerManagementReset(conn, dev);
+
     /* Bus reset is not an option with the root bus */
-    if (dev->bus != 0)
+    if (ret < 0 && dev->bus != 0)
         ret = pciTrySecondaryBusReset(conn, dev);
 
-    /* Next best option is a PCI power management reset */
-    if (ret < 0 && dev->has_pm_reset)
-        ret = pciTryPowerManagementReset(conn, dev);
-
     if (ret < 0)
         pciReportError(conn, VIR_ERR_NO_SUPPORT,
                        _("No PCI reset capability available for %s"),
-- 
1.6.2.5