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



On 2014/8/25 13:18, Chen, Tiejun wrote:
On 2014/8/24 19:12, Michael S. Tsirkin wrote:
On Fri, Aug 22, 2014 at 09:06:20AM +0800, Chen, Tiejun wrote:
On 2014/8/22 0:16, Konrad Rzeszutek Wilk wrote:
On Thu, Aug 21, 2014 at 09:28:28AM +0800, Tiejun Chen wrote:
Currenjly this ISA bridge should be fixed at 1f.0, and pass the

Currently

Fixed.


real vendor/device ids as the driver expect.

Could you add a bit more description to this patch please? Explain
the rationale, etc.

So rephrase as follows:

xen:i386:pc_piix: create isa bridge specific to IGD passthrough

Currently IGD drivers always need to access PCH by 1f.0,

OK

and
identify PCH type with its own real vendor/device ids. This type
value help driver initialize correctly.

instead: PCH vendor/device id is used to identify the card.

Okay.



Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
---
  hw/i386/pc_piix.c | 24 +++++++++++++++++++++++-
  1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 7710724..b131fa3 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -50,7 +50,8 @@
  #include "cpu.h"
  #include "qemu/error-report.h"
  #ifdef CONFIG_XEN
-#  include <xen/hvm/hvm_info_table.h>
+#include <xen/hvm/hvm_info_table.h>
+#include <hw/xen/xen-host-pci-device.h>
  #endif

  #define MAX_IDE_BUS 2
@@ -463,6 +464,26 @@ static void pc_xen_hvm_init(MachineState
*machine)
      }
  }

+static void xen_igd_passthrough_isa_bridge_create(PCIBus *bus)
+{
+    struct PCIDevice *dev;
+    XenHostPCIDevice hdev;
+    int r = 0;
+
+    /* This shoudl be fixed at 1f.0 then pass vendor/device ids.

should

However I would remove the comment as it does not add anything extra
to the function. It is pretty clear what it is doing.

What would help is if you said:

Must be fixed at 1f.0 because .. bla blah

Like the patch description, so what about this,

     /* Currently IGD drivers always need to access PCH by 1f.0, and
      * identify PCH type with its own real vendor/device ids.
      */

Thanks
Tiejun


+     */
+    dev = pci_create_simple(bus, PCI_DEVFN(0x1f, 0),
+                            "xen-igd-passthrough-isa-bridge");
+    if (dev) {
+        r = xen_host_pci_device_get(&hdev, 0, 0, PCI_DEVFN(0x1f,
0), 0);
+        if (!r) {
+            pci_config_set_vendor_id(dev->config, hdev.vendor_id);
+            pci_config_set_device_id(dev->config, hdev.device_id);

Can you, instead, implement the reverse logic, probing
the card and supplying the correct device id for PCH?


Here what is your so-called reverse logic as I already asked you
previously? Do you mean I should list all PCHs with a combo illustrated
with the vendor/device id in advance? Then look up if we can find a

Michael,

Could you explain this exactly? Then I can try follow-up your idea ASAP if this is necessary and possible.

Thanks
Tiejun

matched PCH? If yes, what is that benefit you expect in passthrough
case? Shouldn't we pass these info to VM directly in passthrough case?

Thanks
Tiejun




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