[PATCH v4 08/11] vpci/header: emulate PCI_COMMAND register for guests

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Add basic emulation support for guests. At the moment only emulate
PCI_COMMAND_INTX_DISABLE bit, the rest is not emulated yet and left
as TODO.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
Since v3:
- gate more code on CONFIG_HAS_MSI
- removed logic for the case when MSI/MSI-X not enabled
---
 xen/drivers/vpci/header.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index 34158da2d5f6..64cfc268c341 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -459,6 +459,22 @@ static void cmd_write(const struct pci_dev *pdev, unsigned int reg,
         pci_conf_write16(pdev->sbdf, reg, cmd);
 }
 
+static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
+                            uint32_t cmd, void *data)
+{
+    /* TODO: Add proper emulation for all bits of the command register. */
+
+#ifdef CONFIG_HAS_PCI_MSI
+    if ( pdev->vpci->msi->enabled )
+    {
+        /* Guest wants to enable INTx. It can't be enabled if MSI/MSI-X enabled. */
+        cmd |= PCI_COMMAND_INTX_DISABLE;
+    }
+#endif
+
+    cmd_write(pdev, reg, cmd, data);
+}
+
 static void bar_write(const struct pci_dev *pdev, unsigned int reg,
                       uint32_t val, void *data)
 {
@@ -631,8 +647,9 @@ static int init_bars(struct pci_dev *pdev)
     }
 
     /* Setup a handler for the command register. */
-    rc = vpci_add_register(pdev->vpci, vpci_hw_read16, cmd_write, PCI_COMMAND,
-                           2, header);
+    rc = vpci_add_register(pdev->vpci, vpci_hw_read16,
+                           is_hwdom ? cmd_write : guest_cmd_write,
+                           PCI_COMMAND, 2, header);
     if ( rc )
         return rc;
 
-- 
2.25.1