Re: [PATCH] PCI: dwc: Added link up check in map_bus of dw_child_pcie_ops

[Lorenzo Pieralisi]

On Fri, Sep 18, 2020 at 09:27:40AM -0600, Rob Herring wrote:

[...]

> > > Maybe a link down just never happens once up, but if so, then we only need
> > > to check it once and fail probe.
> >
> > Many customers connect the FPGA Endpoint, which may establish PCIe link
> > after the PCIe enumeration and then rescan the PCIe bus, so I think it should
> > not exit the probe of root port even if there is not link up during enumeration.
> 
> That's a good reason. I want to unify the behavior here as it varies
> per platform currently and wasn't sure which way to go.

We don't need to fail probe - just skip enumeration. Is there an IRQ
event associated with link coming up ? Scanning the bus can be done
upon link-up IRQ.

For platforms that forward the link down as an SError this still does
not solve the problem (if the link goes down unexpectedly) but I
question their design in the first place, this patch does not fix their
behaviour regardless.

Lorenzo