Re: [Qemu-devel] [v7][PATCH 03/10] piix: create host bridge to passthrough

[Gerd Hoffmann <kraxel@redhat.com>]

On Mi, 2015-03-18 at 17:06 +0800, Tiejun Chen wrote:
> Implement a pci host bridge specific to passthrough. Actually
> this just inherits the standard one. And we also just expose
> a minimal real host bridge pci configuration subset.

> +/* Here we just expose minimal host bridge offset subset. */
> +static const IGDHostInfo igd_host_bridge_infos[] = {
> +    {0x08, 2},  /* revision id */
> +    {0x2c, 2},  /* sybsystem vendor id */
> +    {0x2e, 2},  /* sybsystem id */
> +    {0x50, 2},  /* SNB: processor graphics control register */
> +    {0x52, 2},  /* processor graphics control register */
> +    {0xa4, 4},  /* SNB: graphics base of stolen memory */
> +    {0xa8, 4},  /* SNB: base of GTT stolen memory */
> +};

Hmm, no vendor/device id here?  Will the idg guest drivers happily read
graphics control registers from i440fx even though this chipset never
existed in a igd variant?

[ just wondering, if it works that way fine, it certainly makes things
  easier for the firmware which uses host bridge pci id to figure
  whenever it is running @ i440fx or q35 ].

> +static int igd_pt_i440fx_initfn(struct PCIDevice *pci_dev)
> +{
> +    uint32_t val = 0;
> +    int rc, i, num;
> +    int pos, len;
> +
> +    num = ARRAY_SIZE(igd_host_bridge_infos);
> +    for (i = 0; i < num; i++) {
> +        pos = igd_host_bridge_infos[i].offset;
> +        len = igd_host_bridge_infos[i].len;
> +        rc = host_pci_config_read(pos, len, val);
> +        if (rc) {
> +            return -ENODEV;
> +        }
> +        pci_default_write_config(pci_dev, pos, val, len);
> +    }
> +
> +    return 0;
> +}

Nothing i440fx specific in here, just copying some host bridge pci
config space bits.  I guess we can sub-class the q35 host bridge the
same way and even reuse the init function?

> +#define TYPE_IGD_PASSTHROUGH_I440FX_PCI_DEVICE "xen-igd-passthrough-i440FX"

One xen leftover slipped through here.

cheers,
  Gerd