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Re: [Xen-devel] [Qemu-devel] [RFC][PATCH 2/2] xen:i386:pc_piix: create isa bridge specific to IGD passthrough

On 2014/11/17 18:13, Michael S. Tsirkin wrote:
On Mon, Nov 17, 2014 at 05:42:12PM +0800, Chen, Tiejun wrote:
On 2014/11/17 17:25, Michael S. Tsirkin wrote:
On Mon, Nov 17, 2014 at 04:48:32PM +0800, Chen, Tiejun wrote:
On 2014/11/17 14:10, Michael S. Tsirkin wrote:
On Mon, Nov 17, 2014 at 10:47:56AM +0800, Chen, Tiejun wrote:
On 2014/11/5 22:09, Michael S. Tsirkin wrote:
On Wed, Nov 05, 2014 at 03:22:59PM +0800, Tiejun Chen wrote:
Currently IGD drivers always need to access PCH by 1f.0, and
PCH vendor/device id is used to identify the card.

Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>


         if (!pci_dev) {
          pci_config_set_device_id(pci_dev->config, pch_id);

I will address all comments and thanks.

+    }
  /* init */

  static int xen_pt_initfn(PCIDevice *d)
@@ -682,6 +770,9 @@ static int xen_pt_initfn(PCIDevice *d)
          return -1;

+    /* Register ISA bridge for passthrough GFX. */
+    xen_igd_passthrough_isa_bridge_create(s, &s->real_device);
      /* reinitialize each config register to be emulated */
      if (xen_pt_config_init(s)) {
          XEN_PT_ERR(d, "PCI Config space initialisation failed.\n");

Note I will introduce a inline function in another patch,

+static inline int is_vga_passthrough(XenHostPCIDevice *dev)
+    return (xen_has_gfx_passthru && (dev->vendor_id == PCI_VENDOR_ID_INTEL)
+            && ((dev->class_code >> 0x8) == PCI_CLASS_DISPLAY_VGA));


Why bother with all these conditions?
Won't it be enough to check dev->vendor_id == PCI_VENDOR_ID_INTEL?

If this is just used for IGD, its always fine without checking vendor_id.

You need to match device ID to *know* it's IGD.

So after remove that check, I guess I need to rename that as
is_igd_vga_passthrough() to make sense.


There is no need to check class code or xen_has_gfx_passthru flag.
Device ID + vendor ID identifies each device uniquely.


Here I assume vendor ID is always PCI_VENDOR_ID_INTEL so looks you means I also need to check that table to do something like,

        int i;
        int num = ARRAY_SIZE(xen_igd_combo_id_infos);
        for (i = 0; i < num; i++) {
                if (dev->device_id == xen_igd_combo_id_infos[i].gpu_device_id)
                        return 1;
        return 0;

Then we can simplify the subsequent codes based on this, right?


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