Re: [Qemu-devel] [v5][PATCH 2/5] xen, gfx passthrough: create pseudo intel isa bridge

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 25, 2014 at 04:10:44PM +0800, Chen, Tiejun wrote:
> On 2014/6/25 14:45, Michael S. Tsirkin wrote:
> >On Wed, Jun 25, 2014 at 10:17:18AM +0800, Tiejun Chen wrote:
> >>ISA bridge is needed since Intel gfx drive will probe with Dev31:Fun0
> >>to make graphics device passthrough work well for VMM, that only need
> >>to expose this pseudo ISA bridge to let driver know the real hardware
> >>underneath.
> >>
> >>The original patch is from Allen Kay <allen.m.kay@intel.com>
> >>
> >>Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> >>Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> >>Cc: Allen Kay <allen.m.kay@intel.com>
> >>---
> >>v5:
> >>
> >>* Don't set this ISA class property, instead, just fake this ISA bridge
> >>   with 00:1f.0.
> >>
> >>v4:
> >>
> >>* Remove some unnecessary "return" in void foo().
> >>
> >>v3:
> >>
> >>* Fix some typos.
> >>* Improve some return paths.
> >>
> >>v2:
> >>
> >>* Nothing is changed.
> >>
> >>  hw/xen/xen_pt_graphics.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 61 insertions(+)
> >>
> >>diff --git a/hw/xen/xen_pt_graphics.c b/hw/xen/xen_pt_graphics.c
> >>index 461e526..974b7e9 100644
> >>--- a/hw/xen/xen_pt_graphics.c
> >>+++ b/hw/xen/xen_pt_graphics.c
> >>@@ -230,3 +230,64 @@ out:
> >>      g_free(bios);
> >>      return rc;
> >>  }
> >>+
> >>+static uint32_t isa_bridge_read_config(PCIDevice *d, uint32_t addr, int len)
> >>+{
> >>+    return pci_default_read_config(d, addr, len);
> >>+}
> >>+
> >>+static void isa_bridge_write_config(PCIDevice *d, uint32_t addr, uint32_t v,
> >>+                                    int len)
> >>+{
> >>+    pci_default_write_config(d, addr, v, len);
> >>+}
> >>+
> >>+static void isa_bridge_class_init(ObjectClass *klass, void *data)
> >>+{
> >>+    PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
> >>+
> >>+    k->config_read = isa_bridge_read_config;
> >>+    k->config_write = isa_bridge_write_config;
> >>+};
> >
> >You don't need these stubs, just don't fill anything,
> >pci core will use defaults then.
> 
> I guess these stubs are left to extend something in the future. But maybe we
> can remove them now.
> 
> >
> >>+
> >>+typedef struct {
> >>+    PCIDevice dev;
> >>+} ISABridgeState;
> >>+
> >
> >Nor do you need an empty structure if it has no state.
> >
> >>+static TypeInfo isa_bridge_info = {
> >>+    .name          = "pseudo-intel-pch-isa-bridge",
> >>+    .parent        = TYPE_PCI_DEVICE,
> >>+    .instance_size = sizeof(ISABridgeState),
> >>+    .class_init = isa_bridge_class_init,
> >>+};
> >>+
> >>+static void xen_pt_graphics_register_types(void)
> >>+{
> >>+    type_register_static(&isa_bridge_info);
> >>+}
> >>+
> >>+type_init(xen_pt_graphics_register_types)
> >>+
> >>+static int create_pseudo_pch_isa_bridge(PCIBus *bus, XenHostPCIDevice *hdev)
> >>+{
> >>+    struct PCIDevice *dev;
> >>+
> >>+    char rid;
> >>+
> >>+    /* We havt to use a simple PCI device to fake this ISA bridge
> >>+     * to avoid making some confusion to BIOS and ACPI.
> >>+     */
> >
> >A typo and confusing wording above, I'm not really
> >sure what this comment means.
> >Maybe:
> >
> >/* Create a fake ISA bridge device at the location expected by guests. */
> >
> 
> Good comments so thanks so much.
> 
> >
> >>+    dev = pci_create(bus, PCI_DEVFN(0x1f, 0), "pseudo-intel-pch-isa-bridge");
> >>+
> >>+    qdev_init_nofail(&dev->qdev);
> >>+
> >>+    pci_config_set_vendor_id(dev->config, hdev->vendor_id);
> >>+    pci_config_set_device_id(dev->config, hdev->device_id);
> >>+
> >>+    xen_host_pci_get_block(hdev, PCI_REVISION_ID, (uint8_t *)&rid, 1);
> >
> >Host PCI device is the VGA card?
> 
> This is a real ISA bridge.
> 
> >So why does it make sense to get it's vendor/device/revision and
> >stick in the ISA bridge?
> 
> The Intel generation of integrated graphics needs to probe this ISA bridge
> to initialize the i915 driver properly.
> 
> Thanks
> Tiejun

So vendor/device/revision IDs must match real device then?
Stick this in the comment then.

In fact it's exactly what passthrough does.
I wonder if more bits from ./hw/i386/kvm/pci-assign.c
can be reused. How do you poke at the host device? sysfs?



> >
> >Also change rid to uint8_t, you won't need to cast then.
> >
> >>+
> >>+    pci_config_set_revision(dev->config, rid);
> >>+
> >>+    XEN_PT_LOG(dev, "The pseudo Intel PCH ISA bridge created.\n");
> >>+    return 0;
> >>+}
> >>--
> >>1.9.1
> >
> >