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

["Chen, Tiejun" <tiejun.chen@intel.com>]

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@intel.com>
>>>> ---
>>>>   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 
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