[Qemu-devel] [PATCH] QEMU: Mask writes to RO bits in the status reg of PCI config space

[Amit Shah <amit.shah@redhat.com>]

The Status register in the PCI config space has some read-only bits.
Any writes to those bits should be masked out.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
---
 qemu/hw/pci.c |   11 +++++++++++
 qemu/hw/pci.h |   15 +++++++++++++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/qemu/hw/pci.c b/qemu/hw/pci.c
index c93758d..f07892e 100644
--- a/qemu/hw/pci.c
+++ b/qemu/hw/pci.c
@@ -416,6 +416,7 @@ void pci_default_write_config(PCIDevice *d,
             case 0x0b:
             case 0x0e:
             case 0x10 ... 0x27: /* base */
+            case 0x2c ... 0x2f: /* read-only subsystem ID & vendor ID */
             case 0x30 ... 0x33: /* rom */
             case 0x3d:
                 can_write = 0;
@@ -437,6 +438,7 @@ void pci_default_write_config(PCIDevice *d,
             case 0x0a:
             case 0x0b:
             case 0x0e:
+            case 0x2c ... 0x2f: /* read-only subsystem ID & vendor ID */
             case 0x38 ... 0x3b: /* rom */
             case 0x3d:
                 can_write = 0;
@@ -448,6 +450,15 @@ void pci_default_write_config(PCIDevice *d,
             break;
         }
         if (can_write) {
+            /* Mask out writes to reserved bits in registers */
+            switch (addr) {
+            case 0x06:
+                val &= ~PCI_STATUS_RESERVED_MASK_LO;
+                break;
+            case 0x07:
+                val &= ~PCI_STATUS_RESERVED_MASK_HI;
+                break;
+            }
             d->config[addr] = val;
         }
         if (++addr > 0xff)
diff --git a/qemu/hw/pci.h b/qemu/hw/pci.h
index e11fbbf..d25b0ca 100644
--- a/qemu/hw/pci.h
+++ b/qemu/hw/pci.h
@@ -46,6 +46,21 @@ typedef struct PCIIORegion {
 #define PCI_MIN_GNT		0x3e	/* 8 bits */
 #define PCI_MAX_LAT		0x3f	/* 8 bits */
 
+/* Bits in the PCI Status Register (PCI 2.3 spec) */
+#define PCI_STATUS_RESERVED1	0x007
+#define PCI_STATUS_INT_STATUS	0x008
+#define PCI_STATUS_CAPABILITIES	0x010
+#define PCI_STATUS_66MHZ	0x020
+#define PCI_STATUS_RESERVED2	0x040
+#define PCI_STATUS_FAST_BACK	0x080
+#define PCI_STATUS_DEVSEL	0x600
+
+#define PCI_STATUS_RESERVED_MASK_LO (PCI_STATUS_RESERVED1 | \
+                PCI_STATUS_INT_STATUS | PCI_STATUS_CAPABILITIES | \
+                PCI_STATUS_66MHZ | PCI_STATUS_RESERVED2 | PCI_STATUS_FAST_BACK)
+
+#define PCI_STATUS_RESERVED_MASK_HI (PCI_STATUS_DEVSEL >> 8)
+
 struct PCIDevice {
     /* PCI config space */
     uint8_t config[256];
-- 
1.5.6.3