Re: [Qemu-devel] [PATCH v3 0/2] PCI-e device multi-function hot-add support

[Michael S. Tsirkin]

On Wed, Oct 21, 2015 at 04:32:17PM +0800, Cao jin wrote:
> Hello Michael
> 
> On 10/13/2015 09:10 PM, Michael S. Tsirkin wrote:
> >On Tue, Oct 13, 2015 at 07:54:07PM +0800, Cao jin wrote:
> >>
> >>
> >>On 10/13/2015 04:49 PM, Michael S. Tsirkin wrote:
> >>>On Tue, Oct 13, 2015 at 04:41:33PM +0800, Cao jin wrote:
> >>>>Support PCI-e device hot-add multi-function via device_add, just ensure
> >>>>add the function 0 is added last. While allow user to roll back in the
> >>>>middle via device_del, in case user regret.
> >>>
> >>>This patch doesn't seem to account of AIR though.
> >>>
> >>
> >>Yes, but the AIR function seems never be used(nobody calls the function
> >>pcie_ari_init()), so I am a little confused about should it be consindered?
> >
> >Yes please - we'll likely use that in the future. Pls add an API
> >that takes ari into account.
> >
> after analysed the code and read the spec, but still a little confused about
> "add an API that takes ari into account". what is new API for? Could you
> give a detailed description?

You are assuming PCI_FUNC == 0 means function 9.  But the real
rule is: for an express device associated with an upstream port, it's
devfn == 0. For any other device (non express or not connected
to an upstream port) - PCI_FUNC == 0.

I think a reasonable API could be e.g.
bool pci_is_function_0()
with a comment explaining the issues.


> AFAICT now, taking ari into account will affect the "addr" property of PCI
> device(maybe also need a new prop of "ari=on" to enable ari).
> 
> >>>>changelog:
> >>>>1. Flag device as unexposed when func 0 doesn`t exist, via return 0xFF
> >>>>    in case of gratuitous pci bus scan.
> >>>>2. Since device is unexposed to guest, can remove function individually,
> >>>>    without interaction with the guest.
> >>>>
> >>>>Cao jin (2):
> >>>>   enable multi-function hot-add
> >>>>   remove function during multi-function hot-add
> >>>>
> >>>>  hw/pci/pci.c      | 10 ++++++++++
> >>>>  hw/pci/pci_host.c |  6 +++++-
> >>>>  hw/pci/pcie.c     | 38 +++++++++++++++++++++++++-------------
> >>>>  3 files changed, 40 insertions(+), 14 deletions(-)
> >>>>
> >>>>--
> >>>>2.1.0
> >>>.
> >>>
> >>
> >>--
> >>Yours Sincerely,
> >>
> >>Cao Jin
> >.
> >
> 
> -- 
> Yours Sincerely,
> 
> Cao Jin