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

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

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@intel.com>
>>>>>>>> ---
>>
>> [snip]
>>
>>> Cleaner:
>>> 	 if (!pci_dev) {
>>> 		fprintf
>>> 		return;
>>> 	}
>>>           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));
>>>> +}
>>>>
>>>> Thanks
>>>> Tiejun
>>>
>>> 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.
>>
>> Thanks
>> Tiejun
>
> There is no need to check class code or xen_has_gfx_passthru flag.
> Device ID + vendor ID identifies each device uniquely.
>

Yeah.

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,

is_igd_vga_passthugh(dev)
{	
	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?

Thanks
Tiejun