[RFC QEMU PATCH v8 2/2] virtio-pci: implement No_Soft_Reset bit

[Jiqian Chen]

In current code, when guest does S3, virtio devices are reset due to
the bit No_Soft_Reset is not set. After resetting, the display resources
of virtio-gpu are destroyed, then the display can't come back and only
show blank after resuming.

Implement No_Soft_Reset bit of PCI_PM_CTRL register, then guest can check
this bit, if this bit is set, the devices resetting will not be done, and
then the display can work after resuming.

Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
---
 hw/virtio/virtio-pci.c         | 29 +++++++++++++++++++++++++++++
 include/hw/virtio/virtio-pci.h |  5 +++++
 2 files changed, 34 insertions(+)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 05dd03758d9f..8d9fab855c7d 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -2378,6 +2378,11 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error 
**errp)
             pcie_cap_lnkctl_init(pci_dev);
         }
 
+        if (proxy->flags & VIRTIO_PCI_FLAG_PM_NO_SOFT_RESET) {
+            pci_set_word(pci_dev->config + pos + PCI_PM_CTRL,
+                         PCI_PM_CTRL_NO_SOFT_RESET);
+        }
+
         if (proxy->flags & VIRTIO_PCI_FLAG_INIT_PM) {
             /* Init Power Management Control Register */
             pci_set_word(pci_dev->wmask + pos + PCI_PM_CTRL,
@@ -2440,11 +2445,33 @@ static void virtio_pci_reset(DeviceState *qdev)
     }
 }
 
+static bool virtio_pci_no_soft_reset(PCIDevice *dev)
+{
+    uint16_t pmcsr;
+
+    if (!pci_is_express(dev) || !dev->exp.pm_cap) {
+        return false;
+    }
+
+    pmcsr = pci_get_word(dev->config + dev->exp.pm_cap + PCI_PM_CTRL);
+
+    /*
+     * When No_Soft_Reset bit is set and the device
+     * is in D3hot state, don't reset device
+     */
+    return ((pmcsr & PCI_PM_CTRL_NO_SOFT_RESET) &&
+            (pmcsr & PCI_PM_CTRL_STATE_MASK) == 3);
+}
+
 static void virtio_pci_bus_reset_hold(Object *obj)
 {
     PCIDevice *dev = PCI_DEVICE(obj);
     DeviceState *qdev = DEVICE(obj);
 
+    if (virtio_pci_no_soft_reset(dev)) {
+        return;
+    }
+
     virtio_pci_reset(qdev);
 
     if (pci_is_express(dev)) {
@@ -2484,6 +2511,8 @@ static Property virtio_pci_properties[] = {
                     VIRTIO_PCI_FLAG_INIT_LNKCTL_BIT, true),
     DEFINE_PROP_BIT("x-pcie-pm-init", VirtIOPCIProxy, flags,
                     VIRTIO_PCI_FLAG_INIT_PM_BIT, true),
+    DEFINE_PROP_BIT("x-pcie-pm-no-soft-reset", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_PM_NO_SOFT_RESET_BIT, false),
     DEFINE_PROP_BIT("x-pcie-flr-init", VirtIOPCIProxy, flags,
                     VIRTIO_PCI_FLAG_INIT_FLR_BIT, true),
     DEFINE_PROP_BIT("aer", VirtIOPCIProxy, flags,
diff --git a/include/hw/virtio/virtio-pci.h b/include/hw/virtio/virtio-pci.h
index 4d57a9c75130..c758eb738234 100644
--- a/include/hw/virtio/virtio-pci.h
+++ b/include/hw/virtio/virtio-pci.h
@@ -44,6 +44,7 @@ enum {
     VIRTIO_PCI_FLAG_AER_BIT,
     VIRTIO_PCI_FLAG_ATS_PAGE_ALIGNED_BIT,
     VIRTIO_PCI_FLAG_VDPA_BIT,
+    VIRTIO_PCI_FLAG_PM_NO_SOFT_RESET_BIT,
 };
 
 /* Need to activate work-arounds for buggy guests at vmstate load. */
@@ -80,6 +81,10 @@ enum {
 /* Init Power Management */
 #define VIRTIO_PCI_FLAG_INIT_PM (1 << VIRTIO_PCI_FLAG_INIT_PM_BIT)
 
+/* Init The No_Soft_Reset bit of Power Management */
+#define VIRTIO_PCI_FLAG_PM_NO_SOFT_RESET \
+  (1 << VIRTIO_PCI_FLAG_PM_NO_SOFT_RESET_BIT)
+
 /* Init Function Level Reset capability */
 #define VIRTIO_PCI_FLAG_INIT_FLR (1 << VIRTIO_PCI_FLAG_INIT_FLR_BIT)
 
-- 
2.34.1