Re: [Xen-devel] [PATCH V2] Xen/pciback: Implement PCI slot or bus reset with 'do_flr' SysFS attribute

[Govinda Tatti <govinda.tatti@xxxxxxxxxx>]

On 11/30/2017 8:46 AM, Jan Beulich wrote:
> > > > On 30.11.17 at 15:15, <govinda.tatti@xxxxxxxxxx> wrote:
> > On 11/30/2017 2:27 AM, Jan Beulich wrote:
> > > > > > On 29.11.17 at 18:38, <govinda.tatti@xxxxxxxxxx> wrote:
> > > > > > In the case of bus or slot reset, our goal is to reset connected PCIe
> > > > > > fabric/card/endpoint.
> > > > > > The connected card/endpoint can be multi-function device. So, same
> > > > > > walk-through and checking
> > > > > > is needed irrespective of type of reset being used.
> > > > > I don't follow: The scope of other devices/functions possibly
> > > > > affected by a reset depends on the type of reset, doesn't it?
> > > > For PCIe platforms, both slot and bus reset endup resetting all connected
> > > > device/functions on thesecondary bus (behind the root-port or
> > > > downstream-port).
> > > According to my understanding this contradicts the comment
> > > ahead of pci_reset_slot(), which talks of multiple slots per bus.
> > > In such a setup, I can't see why resetting on slot would affect
> > > other slots on the same bus. At the same time the comment
> > > says that the slot reset may resolve to a bus one when there's
> > > just a single slot on the bus.
> > For legacy PCI/PCI-X, we can have multiple slots per bus but not with
> > PCI-Express
> > (each link will be on a separate bus).
> Is that true even for root complex integrated end points? A
> random system's lspci output doesn't seem to agree with what
> you say. A typical example would be USB controllers all sitting
> on bus 0, but having different slot numbers. You clearly won't
> be able to ever bus-reset these, and if you checked all devices
> on bus 0 you would then also not be able to slot-reset them.
Here, slot reset refers to any PCIe slot that implements or supports
hotplug feature. The slot reset ultimately invokes "pciehp_reset_slot()".
W.r.t integrated endpoints, these can be reset either through FLR or
secondary bus reset methods only.

Cheers
GOVINDA

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