Re: [Qemu-devel] [PATCH v5 2/2] enable multi-function hot-add

[Cao jin]

Hi Michael
    Thanks for your quick response

On 10/27/2015 05:47 PM, Michael S. Tsirkin wrote:
> On Tue, Oct 27, 2015 at 05:39:01PM +0800, Cao jin wrote:
> > > > > static
> > > > > bool pcie_has_upstream_port(PCIDevice *dev)
> > > > > {
> > > > >      PCIDevice *parent_dev = pci_bridge_get_device(pci_dev->bus);
> > > > >
> > > > >      /*
> > > > >       * Device associated with an upstream port.
> > > > >       * As there are several types of these, it's easier to check the
> > > > >       * parent device: upstream ports are always connected to
> > > > >       * root or downstream ports.
> > > > >       */
> > > > >      return parent_dev &&
> > > > >             pci_is_express(parent_dev) &&
> > > > >                 parent_dev->exp.exp_cap &&
> > > > >                 (pcie_cap_get_type(parent_dev) == PCI_EXP_TYPE_ROOT_PORT ||
> > > > >                 pcie_cap_get_type(parent_dev) == PCI_EXP_TYPE_DOWNSTREAM);
> > > > > }
> > > >
> > > > Assume my understanding is right, which means both ARI and non-ARI device
> > > > have the upstream port(root port or downstream port), could the existence of
> > > > upstream port be the judgment condition?
> > >
> > > This tells us whether we are behind a port that
> > > can address devices in slot != 0.
> >
> > Seems I find something, according to spec: Endpoints are classified as
> > either legacy, PCI Express, or Root Complex Integrated Endpoints. I think
> > this is also what you means in comment "As there are several types of these"
> > And "we are behind a port" means the device is not a Root Complex
> > Integrated, only the other two types can be behind a port.
> >
> > Am I right about this?
>
> No, device can be a bridge itself.

Ah yes, you are saying a PCIe-->PCI(PCI-X) bridge, right?

> It's simple: root and downstream
> ports only have 1 slot (and it's a physical one) so you know there's
> always 1 device there. It could have multiple functions.
Yes, I am aware.
It seems there is no big and obvious error about other understandings in 
last mail:) I just want to get myself totally understood about ARI and 
your implementation before using your code. Thank you very much for your 
time and patience:)

And the v6 is on the way

--
Yours Sincerely,

Cao Jin