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Date: Wed, 21 Jan 2015 11:16:55 +0800
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Subject: Re: [Qemu-devel] [v6][PATCH 08/10] xen,
 gfx passthrough: support Intel IGD passthrough with VT-D
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To: "Michael S. Tsirkin" <mst@redhat.com>, allen.m.kay@intel.com
Cc: yang.z.zhang@intel.com, pbonzini@redhat.com, qemu-devel@nongnu.org, aliguori@amazon.com, rth@twiddle.net

>> +uint32_t xen_igd_pci_read(PCIDevice *pci_dev, uint32_t config_addr, int len)
>> +{
>> +    XenHostPCIDevice dev;
>> +    uint32_t val;
>> +    int r;
>> +
>> +    /* IGD read/write is through the host bridge.
>> +     */
>> +    assert(pci_dev->devfn == 0x00);
>> +
>> +    if (!is_igd_passthrough(pci_dev)) {
>> +        goto read_default;
>> +    }
>> +
>> +    /* Just work for the i915 driver. */
>> +    switch (config_addr) {
>> +    case 0x08:        /* revision id */
>> +    case 0x2c:        /* sybsystem vendor id */
>> +    case 0x2e:        /* sybsystem id */
>> +    case 0x50:        /* SNB: processor graphics control register */
>> +    case 0x52:        /* processor graphics control register */
>> +    case 0xa0:        /* top of memory */
>
> Is this host physical memory? If yes how can using it in guest work?

This is just a threshold value, not a start or end address :)

>
>> +    case 0xa4:        /* SNB: graphics base of stolen memory */
>> +    case 0xa8:        /* SNB: base of GTT stolen memory */
>
> Same question for above two.

I shouldn't matter since I remember we already discussed this previously 
but I can't sort out this from those emails now.

Allen,

Could you reexplain this?

>
>> +        break;
>> +    default:
>> +        /* Just gets the emulated values. */
>> +        goto read_default;
>> +    }
>> +
>> +    /* Host read */
>> +    r = xen_host_pci_device_get(&dev, 0, 0, 0, 0);
>> +    if (r) {
>> +        goto err_out;
>> +    }
>> +
>> +    r = xen_host_pci_get_block(&dev, config_addr, (uint8_t *)&val, len);
>> +    if (r) {
>> +        goto err_out;
>> +    }
>> +
>> +    xen_host_pci_device_put(&dev);
>> +
>> +    return val;
>> +
>> +read_default:
>> +    return pci_default_read_config(pci_dev, config_addr, len);
>> +
>> +err_out:
>> +    XEN_PT_ERR(pci_dev, "Can't get pci_dev_host_bridge\n");
>> +    return -1;
>> +}
>
> Do any of the above registers change with time?

Think about we just provide read ops, so they're not changed based on my 
experiential.

> Does it work if we just read them when device is created
> and put in dev->config?

I think this is a good idea so I will go there and thank you.

Tiejun